Term
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Definition
2,4-dichlorophenoxyacetic acid
An herbicide which selectively controls broadleaf weeds in grasses. Its margin of tolerance is broad. Requires a rate of around 1 kg/ha. Has rapid degradation in the soil. Has low root absorption in low pH soil, because the herbicide is present in its protonated form. Enters the phloem using an IAA (auxin) carrier; the plant perceives it as auxin, and allows it through the plasma membrane. Discovered in England and USA in the early 1940s as part of war efforts, intended to be used on enemy crops. It was never used as a weapon in WWII, but was later released commercially as an herbicide. It can be mixed with a diesel carrier, and this was used when it was first released. In the 1990s it was banned. |
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Term
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Definition
| It is converted into 2,4-D inside the cells of broadleaf weeds. |
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Term
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Definition
| The thirds step of herbicide action. A process that an herbicide must go through to be effective. May occur on the leaves or the roots. |
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Term
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Definition
| When an herbicide disrupts a metabolic process so that a toxic molecule is not catalyzed by an enzyme, so it accumulates in the cell. Symptomology is quicker than with starvation. |
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Term
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Definition
| An herbicide that can be used to control wild oats. It was sold in pellet formation, and then liquid formation, each time claiming to be better. |
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Term
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Definition
Activator
Spreader
Surfactant
Wetting agent
An ingredient added to the formulation of an herbicide which increases its retention. It reduces the surface tension of the fluid, creating more "relaxed" droplets. Allows droplets of water to spread over the leaf without running off. Increases surface area for penetration of the herbicide. Without it, water droplets would bead out or bounce off the leaf surface. It spreads the herbicide out, and helps dissolve the cuticle, increasing penetration of water-soluble herbicides. May be part of the herbicide formulation, or may need to be added. Addition to normally safe herbicides can sometimes destroy its selectivity, causing damage to the crop. Tends to be not as tightly regulated as herbicide active ingredients. Includes crop oil and oil concentrates. |
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Term
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Definition
| A soil-herbicide interaction. When a thin layer of the chemical adheres to a soil colloid or soil organic matter. The chemical sticks to the soil surface. An electromagnetic interaction, like a magnet, occurs with the charged molecule. Adsorbed herbicides are unavailable to plant absorption, leaching, and biodegradation. Depends on soil type, moisture, CEC, and porosity. If adsorption is too high, there is no weed control. Moderate adsorption leads to loosely bound chemical with no availability to plants. Weak adsorption leads to leaching of the chemical. The herbicide may have desorption back into the soil solution. Benefits include: prevents leaching and biodegradation, and may reduce crop injury. Negative effects include reduction in weed control. |
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Term
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Definition
| A mixture of 2,4-D and 2,4,5-T. The defoliant (herbicide) used most by the USA army during the Vietnam War. It has long-lasting negative effects on people. |
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Term
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Definition
| A drug that is filtered out by the liver. Exposure over time leads to more alcohol dehydrogenase in the liver, and the person can drink more alcohol without being affected. Alcohol is illegal in Iran, but people still make moonshine. One Iranian fellow came to Canada and drank vodka, but he was okay because he was used to drinking moonshine! |
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Term
| Alternate tillage systems |
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Definition
Conservation tillage
Reduced tillage
A form of tillage. Includes a range of procedures. Must leave at least 30% of the soil covered with crop residue. Done with heavy-duty cultivators, mulch tiller/soil savers, or a chisel. Reduces soil erosion; more plant residues on the surface stop movement of the soil into streams. Reduces time, energy, and capital outlay. Does not necessarily require more herbicides, but may require different herbicides. Weed populations shift from annuals which do well in tilled soil, to perennials which do well in less disturbed soils. |
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Term
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Definition
Erigeron annuus
Family Asteraceae. An annual, but may be a biennial. Found in forage and cereals. Has a different leaf shape from Canada fleabane, with a toothier margin. Leaves are arranged alternately, with a looser habit. Flowers are daisy-like.
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Term
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Definition
Sonchus oleraceus
Family Asteraceae. An annual. Reproduces by seed only. Leaves are round, with sharp, spiny margins. The stem is relatively hairless, with some small hairs near the top. Leaves lack rounded lobes and waxy surface of nodding thistle.
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Term
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Definition
| A family of plants. Includes carrot (and wild carrot), parsnip, celery, spices, and poisonous weeds including hogweed. The inflorescence is an umbel, with many flowers attached to one point, and arranged out like an umbrella. |
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Term
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Definition
| A continuous network within the cell wall and intercellular spaces, and the interconnecting cells of the xylem. A non-living system outside of the symplast. Molecules may move through it, and it is the main pathway for transport of water and nutrients. pH is 5.5. |
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Term
| Aryloxyphenoxypropanoates |
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Definition
| An herbicide which inhibits the enzyme acetyl-CoA carboxylase (ACCase), but is chemically different from cyclohexanedione. |
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Term
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Definition
| An herbicide which kills grasses. It degrades spontaneously at -20ºC in methyl solution. |
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Term
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Definition
Aster family
Composite family
Often found on roadsides. |
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Term
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Definition
| An herbicide which allows for selective control of most weeds in corn and sorghum. Introduced in 1952. Most weeds are slow to metabolize it, but corn, sorghum, rice, and wheat have an enzyme which breaks it down fast enough to survive treatment, by adding a group that makes it stable. In oats and wild oats, the deactivation reaction is very slow and is reversible, making an ester conjugate; there is always some amount of the active form, and the plant dies. The chemical mimics plastoquinone. Used at a rate of 1 - 4 kg active/ha. Has slow degradation in the soil. Can harm pumpkins and soybeans. |
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Term
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Definition
| Can be lost to volatilization if the soil becomes too hot. Includes: Agent Orange; Dicamba; 2,4-D; 2,4-DB; 2,4,5-T; and MCPA. |
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Term
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Definition
Echinochloa sp.
Family Poaceae. A weed which is tolerant to flooding.
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Term
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Definition
| A safener which may be added to Dual to increase its safety in corn. It helps with the conjugation process of the herbicide. |
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Term
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Definition
| An inundative biological control used for mallow in strawberries and orchards. Used in Western Canada. A Colletotrichum fungus. It was developed in Canada, used in the USA, and then came back to Canada. Introduced in 1995, and failed shortly after reaching market. It was withdrawn by the company in 1996 because they couldn't make enough money. The product was too expensive for growers, $30/ac, and the market was too small. |
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Term
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Definition
| Some plastics labelled as biodegradable fragment into microplastic fibres. |
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Term
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Definition
Microbial degradation
A form of degradation of herbicide in the soil. Breakdown by microorganisms, such as bacteria and fungi. The herbicide needs to be in the soil solution, where it is absorbed by the organisms and used as a carbon source. Reduced by soil adsorption. Enhanced by heat, moisture, and oxygen. The most common type of herbicide degradation. |
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Term
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Definition
| Use of live organisms to control weeds. Use of natural enemies to reduce populations of target weeds. Generally, the enemies are insects or pathogens. May include use of livestock to eat weeds (cattle, sheep, goats, geese), and fish for aquatic weeds. Can be fashionable and desired; it is natural, using living things. Can sometimes refer to use of products derived from living organisms. Includes classical and inundative biological control. |
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Term
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Definition
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Term
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Definition
| Herbicides including paraquat and diquat. |
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Term
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Definition
| Copper (II) sulfate (CuSO4) and slaked lime (Ca(OH)2). Used in 1896 to control diseases in grapes. Found that it also killed mustard in cereals. Applied at a rate of 10 - 20 kg/ha. |
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Term
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Definition
| A process that destroys weeds during mechanical control. Separates root from the rest of the plant. A direct control weeds. |
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Term
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Definition
Plantago major
Family Plantaginaceae. A perennial. Found in turf and no-till systems. Has resilient roots. The leaf blade is broad, round, and thick. It can be trampled on and survive. Grows in a rosette, until it forms a scape with a spike of small green flowers. Produces capsules with many small seeds. Often it is mowed down and cannot flower.
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Term
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Definition
Rhamnus sp.
Family Rhamnaceae. An invasive weed. It will grow back if cut down. Can be controlled by applying glyphosate to the cut stem, or painting herbicides onto the bark.
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Term
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Definition
Cirsium vulgare
Family Asteraceae. A biennial. It differs from Canada thistle in that its young leaves have spines. Its mature laves are very spiny, with hairy, divided margins, darker green than Canada thistle. The flower head is similar to Canada thistle, but is larger, and has spines. There has been research in North America for classical biological control.
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Term
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Definition
| A type of fire and heat control. Used in crops, right-of-ways, ditches, and roadsides. In cropping, its efficacy is dubious; there is little kill of weed seeds, and loss of organic matter. Controlled burning of underbrush in forestry stands can prevent forest fires. |
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Term
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Definition
Sutan
An herbicide. Continued use has led to "history soils" and poor weed control in the 1960s and 70s. There is a buildup of microorganisms that rapidly break it down, and continued use encourages their growth. Effectiveness may be improved after waiting a few years for these bacterial populations to decrease. |
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Term
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Definition
Cactoblastis cactorum
An insect from Argentina. Introduced to Australia for classical biological control of prickly pear. The most successful case of biological control, and a classical example showing that the approach can work. It lays eggs in the cactus, and larvae chew the inside. It also spreads a pathogen to the cacti. Only a few moths were released, and they reproduced in the wild. |
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Term
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Definition
| An herbicide used to control thistles in the 1930s. |
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Term
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Definition
| The layer within the plant stem which produces secondary growth. It produces xylem and phloem cells. |
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Term
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Definition
Conyza canadensis
Family Asteraceae. An annual or winter annual. Reproduces by seed only. Young and mature leaves are hairy. Begins as a rosette with wide, hairy leaves. Produces flower stalks with narrow leaves, and small yellow-green flowers. Flower stalk may be fairly tall. Produces wind-dispersed seeds. Leaves are hairier than Canada goldenrod.
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Term
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Definition
Solidago canadensis
Family Asteraceae. A perennial. Has vegetative propagation with rhizomes. Found on roadsides. Young plants resemble fleabane. Leaves have a toothy margin. Earlier leaves near the base are wider than later-forming leaves, which are smaller and narrower. Leaves are less hairy than Canada fleabane. Has dense clusters of yellow flowers, with a "pyramid" shape at the top of the plant.
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Term
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Definition
Cirsium arvense
Family Asteraceae. A perennial. Has vegetative propagation with horizontal roots. Its young leaves are less bumpy and spiny than those of bull thistles. The mature leaves are lighter green than bull thistle, and the leaf surface is smooth. The flower head lacks spines. In Nova Scotia it was controlled with insects which ate the flowers; it was unsuccessful because the plants can reproduce with horizontal roots.
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Term
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Definition
| A factor which can affect the retention of an herbicide. In most cases the carrier is water, which beads out on waxy leaves and may run off. In special cases, such as herbicides sprayed on bushes and trees, oil can be used as a carrier to avoid this. |
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Term
| Carrier-mediated transport |
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Definition
| A way that phloem-mobile herbicides may enter the phloem. Energy-dependent. Includes 2,4-D and glyphosate. |
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Term
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Definition
Daucus carota
Family Apiaceae. It is the same species as wild carrot, but a variety with a larger, orange root. There are other varieties with white, purple, or yellow roots.
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Term
| Causing seeds to germinate |
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Definition
| A process that destroys weeds during mechanical control. Reduces seed populations. Working the soil will stimulate seeds near the surface to germinate. New seeds brought to the surface can be destroyed by further tillage. An indirect control of weeds. |
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Term
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Definition
| Use of chemicals or molecules to control weeds. The most widely used form of control. Includes herbicides, vinegar, and lactic acid. First began with the Romans, who used ash or salt to clear roads, and to destroy the croplands of enemies. Early chemicals were corrosive materials that were not selective, left residues, required high rates, and had a harsh effect, causing osmosis or pH problems in the soil. From 1940 to 1945, war efforts in England and USA involved research on substances that regulate plant growth, resulting in the discovery of 2,4-D and MCPA. A large range of grass-selective herbicides were introduced from 1978 to 1985, controlling grasses in broad-leaved crops and some cereals. As chemical control progresses, the amounts of active ingredient applied per hectare is decreasing. Very few new herbicides have been introduced in the past two years, because the cost of development and registration has become prohibitive, costing $60 - 500 million over 8 - 10 years. All the modes of action have already been discovered, and it is hard to find new herbicides. |
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Term
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Definition
| A form of degradation. The herbicide spontaneously breaks down, not mediated by any organism. |
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Term
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Definition
Cichorium intybus
Family Asteraceae. Begins as a rosette stage which looks very similar to dandelion, and may be difficult to distinguish until later stages, when it becomes erect with coarse, whiskery hairs. Produces a milky sap. Flowers are bright blue.
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Term
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Definition
Glean
An herbicide which provides efficient weed control at a very low rate. Released in 1980, followed by a range of other sulfonylureas. |
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Term
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Definition
| Beetles introduced as classical biological control for St. John's wort in the 1940s. Two species were introduced. They eat the stems and leaves of the plant at night to avoid photosensitivity caused by the plant. May be a pest in cultivated fields of St. John's wort, and not much information is available for how to get rid of them, since they are usually considered a beneficial insect. |
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Term
| Classical biological control |
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Definition
Inoculative biological control
Introduction of a pathogen or insect to the habitat of a target weed. An old technique. Mostly used for introduced weeds that proliferate in the absence of natural enemies. An enemy is introduced, and balance is restored. Gradual clearing and weakening of invading weeds allows for re-establishment of natural species. The enemy is found in the country of origin of the target weed. Aims not for eradication, but the reduction of target weed populations to a level where they are better and more easily managed. Agents are powerful once established. Agents are in equilibrium with the target and no further introduction is necessary; cost-effective once established. Not appealing to private companies, because customers need not return. Usually community- or government-driven. Useful in pasture and rangeland because other methods may be too costly or impractical on such large areas. Requires a stable environment; well-suited to orchards and pastures. Programs can be expensive: costs involved in scouting of agents overseas, and intensive screening of agents in quarantine facilitates to make sure it won't attack non-target organisms such as crops or beneficial plants. Expensive to develop. You must find a control organism, prove it attacks only the target, and find a way to grow it and introduce it. All this must be done before the agent can be tested outdoors, to see if there is potential, and how it reacts to environmental conditions. Specific agents ensure that it is environmentally safe, with no danger to non-target species. Not useful in cultivated field crops with many species of weeds. Compatible with other methods in integrated weed management systems. Works best on perennials; annuals have long periods when the weed is unavailable, and insects may not survive. Target weeds should be very noxious, and not useful or desired in any other situations or locations, because the agent may spread to those places. Target weeds should not be closely related to other useful species. The agent must attack an important part of the plant, and must be adapted to the same temperature range as its target. |
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Term
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Definition
Solanum dulcamara
Bittersweet nightshade
Family Solanaceae. A woody, climbing perennial. Found on fences and shrubs, and in no-till soybeans. Leaves may have one or two lobes at the base. When there is one lobe, the leaf is mitten-shaped. Flowers resemble a tomato flower, but with a yellow centre and purple petals. Some sources say that the berries are poisonous, and others say they are not. The species name means "bitter-sweet"; this may come from the taste of the berries.
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Term
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Definition
| An inundative biological control used for northern joint vetch in rice and soybeans in the USA. Failed shortly after reaching market. |
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Term
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Definition
Tussilago farfara
Family Asteraceae. A perennial weed which grows in dense patches. Flowers resemble those of dandelion. The stem of the flower has purple bracts. One farmer cultivated a patch, and ended up dragging the rhizomes all around, spreading the weed further.
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Term
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Definition
Arctium minus
Family Asteraceae. Leaves are round to oval, with a prominent white vein. Mature leaves are large, and resemble those of rhubarb. Produces purple bur-like flowers with bristles.
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Term
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Definition
Senecio vulgaris
Family Asteraceae. A winter annual. Young leaves are smooth, lacking spines, with a crenate margin. Mature leaves are deeply lobed. Has yellow flowers which form in clusters, and mature into a pappus.
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Term
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Definition
Verbascum thapsus
Devil's tobacco
Family Scrophulariaceae. A biennial. An early successional species. Vaguely resembles tobacco. Grows as a rosette. Does not tolerate disturbance; found in no-till and pasture. Leaves are very velvety. Accumulates thick roots, and then bolts. Has lots small yellow flowers on a tall spike. There are some ornamental varieties with larger flowers. Has dry, brown fruits like a cactus. Produces many tiny seeds. There has been research in North America for classical biological control.
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Term
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Definition
Abrosia artemisiifolia
Family Asteraceae. An annual. Common in Ontario fields. Reproduces by seed only. Emerges in early spring or summer. Its first two leaves are divided into three lobes, unlike those of scentless chamomile. Leaves have a petiole, and are finely segmented and fern-like. The stem is hairy, with an erect habit. Flowers are small and light green, within bowl-shaped bracts.
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Term
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Definition
| A form of metabolism. A group is added to the herbicide, such as an amino acid or sugar. Forms a conjugate with a greater affinity for water. May be sequenced in the vacuole. |
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Term
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Definition
| A form of metabolism. The herbicide is turned into a less active molecule. |
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Term
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Definition
| An herbicide which has limited or no translocation within the plant. Kills tissue only where it is absorbed. Normally, a burn is seen within an hour of application. Good coverage is essential for adequate control. Good for controlling seedlings, but may be ineffective once the crop canopy develops. |
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Term
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Definition
| A continuous sheet of material used as a mulch. Effective against perennials. Includes plastic and paper. |
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Term
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Definition
| Reducing weed impact in the short term. Low intensity management. Altering the balance of competition. Curing the crop of weeds. Includes biological, chemical, cultural, and physical control. |
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Term
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Definition
| A form of tillage. Done with moldboard plows, discs, harrows, or rototillers. Includes primary tillage and secondary tillage. |
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Term
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Definition
| An insect pest which can be found in peppers as well as corn. |
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Term
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Definition
| A process that destroys weeds during mechanical control. Kills the growing point by smothering. Reduced light interception stops photosynthesis. Small weeds growing in rows of a tall crop can be controlled by cultivation, which not only breaks the connection between the plant and the soil, but buries many. A direct control of weeds. |
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Term
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Definition
| Agronomy methods or crop management methods of control. Includes living mulches such as cover crops. |
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Term
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Definition
| The outer layer of the leaf. Contains epicuticular wax and embedded wax, which are hydrophobic. Wax composition depends on the species. There is a more hydrophilic cutin layer underneath, which can become hydrated in conditions of high humidity. Pectin and cellulose strands are very hydrophilic, embedded in the cutin, constituting a preferred route of entry for water-soluble herbicides. Acts as a barrier that prevents water loss, and reduces herbicide absorption in the leaves. 90% of herbicide molecules are stopped by the cuticle. |
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Term
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Definition
| Inhibits the enzyme acetyl-CoA carboxylase (ACCase), but is chemically different from aryloxyphenoxypropanoates. |
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Term
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Definition
| A protein component of photosystem II. Receives two electrons from the QA site on D2. Its QB binding site binds to plastoquinone, and passes the two electrons to it for electron transport. Inhibited by diuron. |
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Term
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Definition
| An herbicide. Introduced in 1954. Used at a rate of 2 - 9 kg active/ha. |
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Term
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Definition
Taraxacum officinale
Family Asteraceae. A perennial. A weed that grows in a rosette which may resemble that of chicory. Has wavy margin in young leaves, and mature leaves are deeply lobed. Produces a milky sap. Has yellow flowers which mature into a pappus. Mowing has no effect on it. A problem in turf. Germination is reduced to zero if mowed before flowering stage. Can be controlled with Sarritor.
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Term
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Definition
| A soil-herbicide interaction. The herbicide breaks down in the soil, transforming into something that is not active. The benefit is that there is no herbicide buildup over time, reducing rotation restrictions. A negative effect is that the weed control period may be too short. Rate of breakdown is affected by: herbicide dose, with higher doses taking longer to degrade; the environment, with warm, moist weather increasing rates of degradation; and the specific herbicide used, with some being more easily degraded than others. Includes photodegradation, biodegradation, and chemical degradation. |
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Term
| Depleting root reserves of perennials |
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Definition
| A process that destroys weeds during mechanical control. To regrow a new shoot, the plant uses the energy stored in its roots; this must be repeated frequently. Fallowing with repeated tillage every 2 - 3 weeks causes root reserves to get very low, and the plant starves and eventually dies. If root reserves are low going into winter, plants are more susceptible to winterkill. Repeated mowing can control milkweed in alfalfa. An indirect control of weeds. |
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Term
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Definition
| When adsorbed herbicide goes back into the soil solution. It becomes available to plants (weeds and crop) and leaching. |
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Term
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Definition
| An inundative control used for stranglevine in orchards in Florida. Failed shortly after reaching market. The product worked too well, and it completely eliminated the weed, also eliminating demand for the product. |
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Term
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Definition
3,6-dichloro-2-methoxybenzoic aid
Banvel
It should not be applied if the temperature is over 20°C, because of volatilization off the leaf. |
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Term
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Definition
| An herbicide which does not affect soybeans. |
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Term
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Definition
Reglone
A non-selective contact herbicide. Introduced in 1961. A bipyridilium. Used as a desiccant in potatoes and beans. |
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Term
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Definition
| Processes which lead to the immediate death of weeds. Includes breaking weeds apart, removing connection with the soil, and covering with soil/smothering. |
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Term
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Definition
| An herbicide which mimics plastoquinone, inhibiting D1. It binds to D1, but does not come off. Water continues to be split, but the electrons accumulate in the chloroplast instead of entering electron transfer, producing reactive oxygen species. The chloroplasts die, and the leaf turns yellow. |
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Term
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Definition
Cuscuta sp.
Family Convolvulaceae. A parasitic plant. If it detects a lower R/FR ratio, such as due to a shading plant, it will grow towards it. Produces structures called haustoria which absorb nutrients from the host plant. Produces a cluster of flowers in mid July to August.
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Term
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Definition
| When pesticide blows in the wind as it is sprayed onto the field. It can harm non-target organisms. In the USA, one cotton farmer shot his neighbor over an incident involving drift! |
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Term
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Definition
Solid formulation
A type of formulation of herbicide. Includes wettable powder (WP), granules (Gr), and wettable granules (WG). Granular formations can avoid runoff in turf. |
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Term
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Definition
Solanum ptychanthum
Family Solanaceae. An annual. Common in Ontario. Tolerates shade from crops. In soybeans, its growth takes off after the plants lose their leaves. Leaves have a purplish colour in the field. May appear like pigweed when young. Flowers resemble a tomato flower, but with a yellow centre and white petals. Berries are green and then turn black. A bad weed in peas and soybeans, because the berries are a similar size. It can smear black stuff onto the harvested seeds.
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Term
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Definition
| A potential method for killing plants. A tractor was created which gives an electric shock to weeds. However, the high voltage in the tractor can be dangerous, and it needs to be very well insulated. |
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Term
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Definition
| An ingredient in the formation of some herbicides. Used for lipid-soluble (hydrophobic) active ingredients, allowing them to mix with water. Otherwise, these chemicals would float to the top or sink to the bottom of the fluid. |
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Term
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Definition
| A factor which can affect the persistence of an herbicide. Includes rainfall, temperature at application, and season-long conditions. |
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Term
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Definition
| A protein which catalyzes a reaction. It fits the substrate into its active site. It may split a molecule apart, or put two together. Herbicides may resemble the substrate of an enzyme, and bind to the active site, potentially becoming stuck, destroying the enzyme. Can form metabolic pathways with other enzymes which may be very complex and branching. |
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Term
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Definition
S-ethyl-N,N-dipropylthiocarbamate
Eptam
An herbicide. Has rapid degradation in the soil. Continued use has led to "history soils" and poor weed control in the 1960s and 70s. There is a buildup of microorganisms that rapidly break it down, and continued use encourages their growth. Effectiveness may be improved after waiting a few years for these bacteria populations to decrease. |
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Term
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Definition
| High intensity management over a long period. |
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Term
| Facultative parasitic plant |
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Definition
| A parasitic plant which does not require a host. Hemiparasitic. |
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Term
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Definition
| Resting the land by not growing crops for a year, or not planting crops in the spring prior to planting winter wheat. Restores soil nutrition. The soil is worked a number of times during the season to prevent perennial weeds. May be done to preserve soil moisture, and to kill weeds with herbicides. There are fuel costs, and the soil can become compacted from high traffic. Can cause soil erosion. No crop is harvested, and there is no profit; it is an investment for future years. Used mainly in Western Canada for moisture preservation. |
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Term
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Definition
Convolvulus arvensis
Family Convolvulaceae. Produces an extensive root system. Has a smaller indent on its younger leaves than hedge bindweed. Basal lobes on mature leaves are more pointed than squared.
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Term
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Definition
Abies sp.
Family Pinaceae. A tree which may be unwanted underneath hydro lines. It cannot be controlled with classical biological control because it is a desired plant in other places.
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Term
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Definition
| A form of mechanical control. Heat or burning that can be used to kill weeds. Can be used to clear land, but it reduces organic matter, and may harm other organisms. Can be used to kill weed seeds. Windrows of straw may be set on fire to control weed seeds. May be used to prepare a seed bed. Cost depends on the price of propane, which can be variable. Includes steam pasteurization, burning, and selective flaming. |
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Term
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Definition
| A form of mechanical control. Used mostly in rice. To be effective, the area must be flooded for at least 3 - 8 weeks with at least 15 - 20 cm of water. The soil must be impermeable, to hold water. Some weeds are tolerant, such as barnyard grass. If it is used intensively, weed populations change to aquatic weeds. |
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Term
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Definition
| An herbicide is never sold pure; it is always used as a formulation containing the active ingredient as well as solvents, emulsifiers and/or diluents. The active ingredient alone is of limited value because it will not get inside the plant. Makes the herbicides easier to use, and allows the active ingredient to mix with water, and have even distribution. Inactive ingredients do not kill the plant, but they help the actual herbicide in some way, making it stable and useful. Includes liquid and dry formulations. |
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Term
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Definition
| A farm machinery company which produces tech that guides tractors through row cultivation, using cameras and GPS. The tractor advances, and moves sideways based on rows. Robot cultivation and engineering. |
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Term
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Definition
N-(phosphonomethyl)glycine
Roundup
A non-selective herbicide that controls perennials and annuals. Introduced in 1974. Systemic, and phloem-mobile, though it can have some movement in the xylem. It enters the phloem using an ortho-phosphate carrier, mimicking phosphate using its phosphate group. Needs to be translocated to underground parts in order to provide efficient control. If too much is applied to leaves, phloem cells will be killed and transport will stop quickly; little herbicide will reach rhizomes, and the plant may grow back. Has very strong soil adsorption, and has no activity in the soil. Its patent expired in 2000, and it is now public property, however the formulation of Roundup is not. In Iran, some farmers taste the product before buying it, to make sure it isn't diluted! |
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Term
| Glyphosate resistant crops |
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Definition
| Introduced in 1996. It was the most important innovation in weed control since 2,4-D and MCPA in 1945. It costs around $250 million to create an herbicide-resistant soybean variety. |
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Term
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Definition
| Loose materials which are spread down in a layer as mulch. Includes woodchips, straw, shredded paper, et cetera. Less effective than continuous mulch for controlling weeds. A lot is required. People usually do not buy enough. Can let perennials grow through, because they have enough reserves. May be used for landscaping. |
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Term
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Definition
Glechoma hederacea
Creeping Charlie
Family Lamiaceae. Has a minty smell. Prostrate growth habit. Leaves are kidney-shaped, arranged oppositely, with small indentations in the margins. Flowers are small and purple. Has vegetative propagation with stolons, which sprout roots as soon as they touch the soil. Invades flower beds, and potted plants. Produces networks of stolons, and can be hard to pull out.
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Term
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Definition
Galinsoga quadriradiata
Family Asteraceae. An annual. Reproduces by seed only. Cotyledons are hairy and club-shaped. Mature leaves are arranged oppositely, and have coarse hairs all over, with a toothed margin. Flower is yellow-green.
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Term
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Definition
Solanum physalifolium
Family Solanaceae. Has an extremely hairy stem. The leaf margin is hairy. Mature leaves feel sticky. Flowers have 5 lobes. Produces poisonous green berries.
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Term
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Definition
| The amount of time it takes for half of a substance to degrade. Half-life of herbicides varies, from 2 weeks to 3 months. Depends on soil type. |
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Term
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Definition
| Structures in dodder which absorb nutrients from the host plant. Also found in powdery mildew. |
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Term
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Definition
Prunella vulgaris
All-heal
Family Lamiaceae. A perennial. Found in turf and flower beds. Flowers look similar to those of ground ivy, but on an inflorescence with brown bracts. Leaves are triangular and narrow, with a square base; spade shaped. Has vegetative propagation with rhizomes, allowing patches to extend sideways.
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Term
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Definition
Calystegia sepium
Family Convolvulaceae. Cotyledons are square with an indentation. Mature leaves have pointed lobes at the base that square off, pointing away from the plant. Flowers are pinkish-white.
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Term
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Definition
| A parasitic plant which is parasitic under some conditions, but also has photosynthesis to some degree. |
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Term
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Definition
Cannabis sativa
Family Cannabaceae. A fibre crop which is the same species as marijuana. It can grow as a volunteer.
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Term
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Definition
Sesbania herbacea
Family Fabaceae. A weed from Arkansas. Modifies its leaf angle over the course of the day. It is better to spray herbicides on it when leaves are parallel to the ground.
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Term
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Definition
Lamium amplexicaule
Family Lamiaceae. Has a U-shaped growth habit. Leaves are arranged oppositely, but look like they wrap fully around the stem. The species name means "around stem".
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Term
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Definition
| A side-effect of using herbicides. The weeds build up resistance over time. |
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Term
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Definition
Weedicides
A form of chemical control, and a type of pesticide. Requires extensive testing for efficacy and safety before it can get to market. May be patented. More herbicides are used than any other type of pesticide, especially in the developing world. Account for approximately 60% of pesticides sold. Advantages include: control of weeds not controlled by mechanical means, within the row in corn and soybeans, in narrow rows of cereals, and in forage and turf; helps adopt reduced tillage, and makes no-till possible; allows for earlier planting and harvest; higher yields; don't need to coordinate with weather and crop staging as with mechanical control; less fuel costs than mechanical control; reduced human labour, covering more hectares/hour using complete mechanization; cost-effective; good against perennial weeds; can be selective; and can be combined with other field operations, such as tillage. Disadvantages include: injury to non-target plants including the crop and plants nearby, persistent herbicide residues can limit rotations, selectivity can be reduced under adverse conditions leading to crop injury, development of herbicide resistance, and potential toxicity to humans, wildlife, livestock, and plants. Continued use of EPTC, butylate, and other related herbicides has led to "history soils" and poor weed control in the 1960s and 70s. The public may have bad connotations regarding herbicides. The chemical acts to inhibit an enzyme that is essential to the plant, killing it. May be used on the crop at the end of the season as a desiccant. Products may react with each other if mixed together. Only a micromolar amount of the active ingredient reaches each plant; amount in the tank is low, only about 100 g/L. May become degraded to inactive forms in the soil or within the plant. At each step of activity, the plant can defend itself from the herbicide, resulting in less herbicide at the target site, and less crop injury. The crop and the weeds should differ at some step, in order to have selectivity. Steps of herbicide action:
1. Interception
2. Retention
3. Absorption
4. Translocation
5. Metabolic degradation
6. Target site |
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Term
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Definition
| A parasitic plant which gets nutrition entirely from another plant. Cannot perform photosynthesis, and may only be obligate parasites. |
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Term
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Definition
Pursuit
An herbicide. Introduced in 1980. Used in soybeans at a rate of 100 g/ha. It is persistent in the soil, restricting rotation. Tomatoes cannot be grown the year after its use. Soybeans are able to break it down fast enough to survive. |
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Term
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Definition
| Row crop cultivators can get weeds between rows of crops, but weeds on the row must be controlled using herbicides, which may be unacceptable for some growers. There are several types of mechanical contraptions invented to mechanically control weeds growing in the row. Applies spring-loaded force sideways, and exploits the difference in strength between the crop and weeds. Requires adjustment and depends on soil type and situation. Includes spyders, torsion weeders, spinners, and spring hoe weeders. In a synchronized cultivation system, a half-moon blade rotates in a circle around each plant. Units are sold separately so farmers need to have a frame custom-made for each particular use. Tools can be used along with conventional sweeps so that both inter-row and on-row cultivation are done at once. In-row cultivators have been used with success in corn, soybeans, and vegetable crops. |
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Term
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Definition
| Processes which rely on future mortality of weeds. Includes depleting root reserves of perennials, and causing seeds to germinate. |
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Term
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Definition
| Insects are considerably different from plants, so insecticides are easier to develop, targeting insect metabolisms, which are much different from that of the crop. |
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Term
| Inundative biological control |
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Definition
Bioherbicides
Mycoherbicides
Started in the 1970s. Isolating a natural pathogen that is pathogenic but occurs at low frequency or attacks weeds late in the season. Usually a fungus, but can be a bacteria. The pathogen is raised artificially, and sprayed early in the season like a chemical herbicide, causing an epidemic in young weeds. Environmentally friendly. Despite extensive research, only a few products have reached market. Companies are interested in it, but it requires a lot of investments with no guarantee of return. Many products fail shortly after reaching market. Reasons include that the products control only one weed, other methods are available, and products are too sensitive to environmental conditions. A pathogen must be found and screened for safety and selectivity. Need to know how to increase spores and store them, when and how to spread them, and the effect of weather. Subjected to the same licencing processes as chemical controls. Future research targeted at economically important weeds is important, ensuring a good market. Specificity may be too high; growers usually want to control a complex of weeds. Difficult to apply on large acreages, and can be expensive; other products do more for less. Fungal diseases thrive in dark, cold, and moist environments; application on dry or sunny days may reduce efficacy. Producing large amounts of live organisms can be tricky; often bad batches are produced. May work well in the lab, but not outdoors. Many have a poor shelf life. |
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Term
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Definition
| Invented planting crops in rows, which allowed for control between rows; this can be done depending on root placement, and how straight you can drive. |
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Term
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Definition
Datura stramonium
Angel's trumpet
Devil's trumpet
Family Solanaceae. Has a bad smell. Plants can grow to be very large, with thick stems. Can be grown as an ornamental. Flowers are large and trumpet-shaped. Leaves have deep, pronounced lobes, with pointed tips. Fruits are spiny. Seeds have an alkaloid which can cause cardiac arrest. Sometimes people eat the seeds, trying to get high.
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Term
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Definition
Mint family
A family of plants. The stem is square: this is not a definite diagnostic, because some other plants have this characteristic. Many have a minty smell. Includes ground ivy, heal-all, and henbit. |
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Term
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Definition
| Movement of herbicide with soil water. Can include lateral leaching (sideways) and reverse leaching (upwards), but the direction is generally downwards. Influenced by soil texture and permeability, volume of water flow, the soil adsorption and water solubility of the herbicide, and weather. Sandy soils and rainfall lead to more leaching potential. Benefits include: soil incorporation, distributing herbicide evenly; enhancing plant-herbicide interception; and removal and reduction of herbicide residues from the soil. Negative effects include: poor weed control if too much herbicide is removed, crop injury when herbicide is transported into their root absorption zone, increased loss by volatility if herbicide is taken to the soil surface, accumulation of herbicide in amounts toxic to otherwise tolerant crop plants, and herbicides in the groundwater. Can lead to loss of "spatial selectivity", and cause damage to the crop. |
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Term
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Definition
| Absorption of an herbicide through the leaf is more difficult than absorption through the root, because the leaf surface is covered with the waxy cuticle layer. Lipid-soluble herbicides may go through the cuticle readily, or get stuck in the cuticle. Water-soluble herbicides are stopped by the cuticle. Cuticle penetration is affected by weather conditions. Higher temperature, air humidity, and soil moisture help leaf penetration of water-soluble herbicides, because it promotes hydration of the cuticle. There is reduced control under stress conditions, such as cold temperatures and low humidity, which make the cuticle thicker and less hydrated. Conditions before spraying can have an influence; plants grown under low light and high humidity have thinner cuticles, and are more receptive to herbicides. |
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Term
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Definition
Euphorbia esula
Family Euphorbiaceae. There has been research in North America for classical biological control.
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Term
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Definition
| There was an incident at a Leamington tomato greenhouse where a disgruntled ex-employee used his old key to sneak in, and add glyphosate to the nutrient supply for the tomatoes. All the plants died, and the police were involved. |
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Term
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Definition
| A type of formulation of herbicide. Includes solution (S), emulsifiable concentrate (EC), and liquid (Li). There may be issues with splashing. |
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Term
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Definition
Malva sp.
Family Malvaceae. Can be controlled using Bio-Mal. Found only in southern Saskatchewan. Because the market for its control is so small, Bio-Mal failed as a business.
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Term
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Definition
Cannabis sp.
Family Cannabaceae. The police might want to find ways to kill marijuana plants using herbicides, in order to start a drug war. The criminals would then have a shoot-out, allowing the police to catch them. One problem with this is that the herbicide-filled marijuana would probably still be sold to users, and could be harmful.
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Term
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Definition
2-methyl-4-chlorophenoxyacetic acid
An herbicide which selectively controls broadleaf weeds in grasses. Discovered in England and USA in the early 1940s as part of war efforts. |
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Term
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Definition
| A type of scale insect which produces a woolly substance. They can be used to produce edible red dye, which some people may wish to avoid for ethical reasons. |
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Term
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Definition
| A subset of physical control. The use of different tools to physically pull out or break weeds. Includes use of hands, tools, or machinery to cut weeds. Hand weeding is the oldest method, which slowly evolved into use of simple tools such as the hoe, and then use of animals and engine power to pull larger implements. Often perceived as an old or ancient way of controlling weeds. Has been evolving, and there are now advanced machines used for mechanical control. Works best if the soil is dry, so that the plants dry out and die. Weeds are destroyed or controlled due to five processes: breaking weeds apart, removing connection with the soil, covering with soil/smothering, depleting root reserves of perennials, and causing seeds to germinate. Includes hand weeding and hoeing, tillage, mowing, mulches, flooding, and fire and heat. Disadvantage include fallowing the soil, dependency on dry weather, root-trimming of the crop, cost of fuel, soil structure, can spread perennials around the field, and slow to control perennials. |
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Term
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Definition
| Some soil-applied herbicides must be immediately incorporated mechanically due to volatilization, including trifluralin. Some herbicides can be incorporated mechanically if the soil is dry, such as metolachlor. Advantages include: does two jobs at once, final tillage and herbicide application; and useful for killing deep-germinating seeds. Disadvantages include: may require extra passes of the field, interfering with timely planting; there is soil moisture loss; compaction of wet soils; not compatible with reduced or no-till systems; and herbicides applied to soil that is cloddy, uneven, or covered with crop residues won't give adequate control. |
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Term
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Definition
| The fifth step of herbicide action. The main step that produces selectivity. As herbicides enter the plant, they may lose activity. Some may be tied up in cellulose, but most inactivation occurs due to metabolism. The herbicide is broken down by the plant by energy-dependent chemical transformation, altering or degrading the herbicide. Enzymes act upon the molecule, changing its structure. Includes conversion and conjugation. Some herbicides are modified by their own target site. The speed at which the plant can degrade the herbicide determines whether it will die. Under stress conditions, such as cold, hot, wet, or dry, the plant may be unable to metabolize the herbicide, leading to crop damage. The plants may be overwhelmed by the dosage of the herbicide, or an interaction with another product. It may be difficult to test interactions, because there are so many products, and interactions may be discovered after market release. Rate of metabolism is influenced by the age of the plant. Most weeds become better at degrading herbicides as they become older, making early treatment important. Can influence toxification. Can be manipulated. |
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Term
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Definition
| The chemical reactions which control life. Includes metabolic degradation of herbicides. |
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Term
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Definition
| A transformed molecule, the result of metabolism. Drug testing looks for the drug in the system, as well as its metabolites. Crop residues can be tested for herbicide metabolites. |
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Term
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Definition
Bromethane
A soil sterilant which can kill dormant seeds. |
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Term
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Definition
Dual
S-metolachlor
A soil-applied herbicide which can be incorporated mechanically if the soil is dry. May be used to control nutsedge. Benoxacor can be added to increase its safety to corn. |
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Term
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Definition
Sencor
4-amino-6-tert-butyl-3-(methylthio)-as-tiazin-5(4H)-one
A soil-applied herbicide which can have leaching in sandy soil, leading to loss of spatial selectivity, and damaging soybeans. The original formulation could not be mixed with Roundup, but Bayer changed the formulation to fix this. |
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Term
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Definition
Asclepias sp.
Family Apocynaceae. Repeated mowing can control it in alfalfa.
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Term
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Definition
A parasitic plant.
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Term
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Definition
| The caterpillar eats milkweed, and accumulates a bitter-tasting toxin from the plant as a defence mechanism. It is not affected by the poison. |
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Term
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Definition
Ipomea sp.
Family Convolvulaceae. An important weed in the USA. Related to sweet potato. Experiments were conducted using autoradiography, X rays, and glyphosate radiolabelled with 14C. The isotope releases electrons which are picked up by the film. You can trace where the herbicide travels in the plant. Found that glyphosate moves into the roots, proving that it is phloem-mobile.
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Term
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Definition
| A soil-herbicide interaction. Includes volatilization and leaching. |
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Term
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Definition
| A form of mechanical control. Includes different types of mowers: rotary for roughland or pasture, reel for turf. Has limited value for weed control, removing only the tops of weeds before flowering. May control annuals in one cut. Can be used to stop seed formation on tall annual or perennial weeds, giving long-term benefits. By forcing regrowth, mowing depletes root reserves of perennials. Like cultivation, controlling perennials takes a number of cuttings due to large root/rhizome reserves. Stimulates production of additional shoots, encouraging lateral buds to grow. Even if it looks like weeds are getting bigger, the more shoots are produced, the faster the root/rhizome reserves are depleted. There is a stimulation of new shoots in turfgrass, which helps to get a denser more competitive turf. Has no effect on weeds that form a rosette, such as dandelion and plantain. Doesn't work if plants produce seed below the mowing height. Tends to encourage weeds with prostrate growth. Mowing after flowers appear does not work, and some weeds set viable seeds within a week of fertilization. |
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Term
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Definition
Artemisia vulgaris
Family Asteraceae. A perennial. A hairy plant. First leaves have two tooth-like indents in the margin. Flowers are similar to those of lamb's quarters. Has bracts around the flower.
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Term
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Definition
| A form of mechanical control. Smothering the crop with an inert organic or inorganic material. Controls weeds, conserves soil moisture, and can protect the crop from becoming dirty. Good for controlling annuals. Efficacy against perennials depends on the material. Before laying it down, the land should be cleared of weeds, and there should be slow water infiltration so soil is wet. It controls weeds by blocking light, preventing germination, and by physically impeding emergence. Organic materials include bark, straw, paper, pine needles, woodchips, and sawdust. Inorganic materials include black plastic, clear plastic, stones, gravel, and aluminum foil. Eventually the mulch may degrade and become a good substrate for weeds, especially if weeds were not controlled before laying the mulch. Have an effect on soil temperature: plastics increase temperature while sawdust or bark decreases it. Organic mulches add to organic matter. Important to be careful to not dig mulch into the soil, because they can mobilize nitrogen. Limited to high-value crops or small acreages, well suited for home gardens. |
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Term
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Definition
Plantago lanceolata
Family Plantaginaceae. The leaves are narrow, without a petiole, with parallel veins, and a hairy surface. Flowers form on a spike which is more condensed, shorter, and pointy than in broad-leaved plantain. Seedlings can look like grass.
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Term
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Definition
Carduus nutans
Family Asteraceae. A biennial. Has a prominent white vein on the leaf. Older leaves are waxier, and have big spines on the margins. Flowers are bright purple, and tend to lean to one side.
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Term
| Non-competitive inhibitor |
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Definition
| An enzyme inhibitor, such as an herbicide, which binds to the enzyme and alters the active site, preventing entry of the substrate. |
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Term
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Definition
Aeschynomene virginica
Sensitive joint-vetch
Family Fabaceae. A weed in rice and soybeans. Can look similar to tufted vetch. Very invasive. Can be controlled with Collego.
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Term
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Definition
| A weed which causes a lot of problems, and is hard to get rid of using normal methods. Good candidates for biological control. |
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Term
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Definition
Cyperus esculentus
Family Cyperaceae. May be controlled with metolachlor.
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Term
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Definition
| A parasitic plant which must attach to a host. It may be a holoparasite or a hemiparasite. |
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Term
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Definition
Leucanthemum vulgare
Family Asteraceae. A perennial. Has vegetative propagation with rhizomes. Cotyledons are oval. Young leaves are spoon-shaped with crenate margins, forming a basal rosette. Mature leaves lack a petiole and have a toothed margin. Flowers are daisy like and resemble those of scentless chamomile.
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Term
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Definition
| A continuous mulch. Newspaper can be laid on the soil. Serves the same function as plastic mulch, but allows for water infiltration. Black paper mulch costs $10 for a roll of 2 x 50 m. |
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Term
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Definition
Gramoxone
N,N'-dimethyl-4,4'-bipyridium dichloride
A non-selective contact herbicide. Introduced in 1962. A bipyridilium. Used in industrial sites, pre-seeding, pre-planting, and post-harvest. Inhibits photosystem II. |
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Term
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Definition
| Plants which obtain nutrients from other plants. Categorized into hemiparasitic holoparasitic plants. Can grow on the surface of cacti. |
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Term
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Definition
Sonchus arvensis
Family Asteraceae. The mature plant has elongated leaves. The flower head has hairs on it.
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Term
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Definition
| Produce food reserves in overwintering structures. By spring the amount of food left is low, but it increases over the summer. Cutting down weeds reduces the amount of food they can produce, reducing survival. |
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Term
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Definition
Carryover
The amount of time that a soil-applied herbicide stays in the soil. It can affect the length of control, the rotation of crops, and the impact of new turf. Factors that influence it include: soil conditions and environmental conditions. |
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Term
| Pest Management Regulatory Agency (PMRA) |
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Definition
| An agency which approves herbicides for use in Canada. A branch of Health Canada. Approves herbicides based on efficacy and safety. The formulations of each pesticide product is reviewed by the PMRA during approval process, but are not released to the public, for business reasons. The USA equivalent is the Environmental Protection Agency (EPA). |
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Term
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Definition
| A chemical which kills pests. Includes herbicides, fungicides, nematicides, insecticides, and rodenticides. Sometimes it can refer only to insecticides. |
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Term
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Definition
| The amount of protons in a solution. The higher the number, the less protons. A logarithmic scale. |
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Term
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Definition
| The fate of a drug once it is in the body. |
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Term
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Definition
| Transports photosynthates (sugars) from source tissues to sink tissues. Living cells; molecules must pass through the plasma membrane to enter the phloem. Cytoplasm of living cells are connected by plastmodesmata. Flow is much slower than in the xylem. The source-sink relationship can change depending on physiological status, changing the flow in the phloem. When conditions for photosynthesis is optimal, flow is the fastest. It is not as easy for herbicides to enter the phloem as the xylem. |
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Term
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Definition
| An herbicide which moves through the phloem with flow of photosynthates, to sink tissues.The preferred type of systemic herbicide, allowing for even distribution of herbicide in the plant, and killing the growing point. Amount of photosynthate being moved depends on the lifecycle, whether there is rapid growth or reproduction. Quality of control is associated with good photosynthesis: high light, warm conditions, and adequate moisture. Actively growing plants will translocate more rapidly. Applied to leaves. Complete coverage of the plant is not needed, but leaves should be alive. Must enter the symplast very early. May enter by simple diffusion, carrier-mediated transport, or weak acid accumulation. The phloem is living, so if the herbicide kills the cells, translocation will stop. To kill underground parts, a slow kill is required because the herbicide needs time to move downwards. Movement is controlled by a more complex process than in the xylem. Ability to move in the phloem depends on physiochemical properties of the herbicide: it should be a water-soluble, weak acid. When applied to mature leaves, it moves downwards towards storage organs. If it falls on younger leaves, it moves upwards towards newly developing parts. If it falls on dying leaves, it does not move. |
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Term
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Definition
| A form of degradation of herbicide in the soil. Breakdown by light. |
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Term
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Definition
| A component necessary for photosynthesis. Located in the thylakoids of the chloroplast, bound to the thylakoid membrane. Includes chlorophyll P680, pheophytin, and proteins D1 and D2. It is inhibited by paraquat. |
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Term
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Definition
Family Poaceae. Grows in wet ditches.
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Term
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Definition
Mechanical control
A form of control. Use of mechanical forces to control weeds, including machines. The physical up-rooting of weeds, or cutting at the soil level. Often used in high value crops for low threshold weeds. Very tedious work. Can be used by organic farmers. More fuel is needed than with chemical control, because of dragging equipment. Works well for annual weeds, however they may come back if the plants are left intact in the field. With perennials, control must be repeated to prevent energy from going into overwintering structures. It may be considered fun, giving a sense of power. Weeds cannot develop resistance to physical control, however repeated control can impose a selection pressure on weeds. It may inadvertently spread perennial weeds by cutting them up. Can be slow, and may require multiple passes. Weeds are easier to pull from dry soil. |
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Term
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Definition
| The pH level at which there are equal amounts of protonated and deprotonated forms of a molecule. |
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Term
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Definition
Plantago sp.
Family Plantaginaceae. A weed that grows in a rosette. Mowing has no effect on it. A problem in turf.
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Term
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Definition
| A continuous mulch. Should be laid down on wet soil. Laid down with a layer/bed shaper machine, which may also add fertilizer. Holes are punched into the plastic and plants are transplanted in. It preserves the moisture underneath. Used mostly in high-value crops. The most popular colour is black, but it comes in different colours including red and blue. In one experiment, red plastic mulch stimulated weed growth. |
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Term
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Definition
| It receives two electrons from D1 of photosystem II for photosynthesis electron transport. Atrazine and diuron mimic it to inhibit D1. |
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Term
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Definition
| Low intensity management over the long term. |
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Term
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Definition
Opuntia sp.
Family Cactaceae. A cactus weed introduced to Australia in the 19th century. In 1925, it infested 30 million hectares of rangeland. It was controlled using a cactus moth. Has barbed hooks which get into the skin. Two native species can be found in Ontario. It is grown as a crop in some areas. The fruit tastes similar to watermelon. If broken, fragments can take root.
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Term
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Definition
| Conventional tillage which involves initial ground breaking to a depth of 15 - 20 cm in preparation for crop production. Done with the moldboard plow or heavy discs. The main aim is not weed control (often done in the fall), but it has an effect on weed populations. Buries weed seeds, which may increase their mortality, but it may bring other seeds to the surface. Efficient against perennials. By cutting or burying the top growth, tillage forces the plants to exhaust the root or rhizome reserves. Must be repeated in a timely fashion during fallow. |
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Term
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Definition
| An herbicide used in rice. |
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Term
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Definition
Acclaim
Excel
An herbicide with an ethyl group which is removed inside the cell, producing a more toxic form. It kills grasses. Metabolized in wheat and barley, but can have some damage in cold weather. May be combined with the safener Super. |
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Term
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Definition
Lythrum salicaria
Family Lythraceae. A perennial weed introduced to Ontario as an ornamental. It escaped, and has invaded many wetlands. Grows in wet ditches. Displaces native flora due to its aggressiveness. Hard to chemically control, so it prompted development of a biological control program with two beetles: Hylobius and Galerucella.
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Term
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Definition
Elymus repens
Family Poaceae. A stretch of wet weather allows it to re-establish after control. If it is not allowed to exceed 8 cm in height, it will be controlled by 18 months.
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Definition
| The length of time after applying an herbicide that it should not rain in order to maintain efficacy. Depends on the herbicide. Generally 6 - 24 hours. Different formulations of the same herbicide may have differing rain fastness. The value may be made up by companies in order to sell herbicides. |
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Definition
| A factor which can affect the retention of an herbicide. Rain after foliar herbicides can wash the herbicides off. The rain-free period required to retain efficacy is rain fastness. Even dew can make a difference; light dew can help distribute herbicide on the leaf surface, but heavy dew can represent 600 L/ha, which may wash off the herbicide. |
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Definition
| Includes oxygen, superoxide anion, peroxide, hydrogen peroxide, hydroxyl radical, and hydroxyl ion. Harmful to cells, and can be toxic. |
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Definition
| A leaf-applied herbicide with some soil activity. Safe to use in corn, but if sprayed on a cold or dry day, the plants may be unable to metabolize the herbicide fast enough. |
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Term
| Removing connection with the soil |
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Definition
| A process that destroys weeds during mechanical control. The weed must dry out. If the soil is wet, or if rainfall occurs son after, remove weeds from the field, because many will take root if left on moist soil. A direct control of weeds. |
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Definition
| The second step of herbicide action. A process that an herbicide must go though to be effective. Once on the leaves, the herbicide must be retained. If retention time is too short, there is less herbicide that goes into the plant, and less chance of good weed control. Greatly affected by environmental factors, as well as volatility of the herbicide, its carrier, spray volume, adjuvants, amount of shoot growth, and rainfall. |
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Definition
| Mice and voles will tunnel underneath the snow in the winter. They may eat the bark of trees. Plastic or mesh can be wrapped on the base of trees to prevent this. |
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Definition
| Herbicides may be absorbed by a plant's roots if they are both in the same soil horizon. The herbicide must be in an available form, which depends on the physiochemical properties of the soil and the herbicide. Occurs mainly in the apical portion of the root, 0.5 - 5.0 mm from the apex. Enter through the root hairs, and must cross the Casparian strip to enter the xylem. Occurs initially very rapidly in a process of diffusion which is not-energy dependent, followed by slower, energy-dependent entry. In most cases the cell membrane is not a significant barrier for herbicides. Affected by factors including binding to root components, and soil pH. Generally, herbicides which are more lipid-soluble are absorbed more rapidly. |
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Term
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Definition
| A tillage implement specifically designed for weed control. Two gangs of wheels have curved spikes that remove small weeds after corn or soybeans have emerged. Pulled at high speeds parallel to the row. The crop is better rooted than the small weeds, which are flicked out. Soil must be dry, and weed seedlings must be very young, without green colour. Helps break any crust, and incorporates herbicides. A single rotary hoe use can reduce plant stand by 5 - 10%. Can be used in row crops or in pre-emergence in cereals. |
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Definition
Scufflers
A tillage implement specifically designed for weed control. Consists of different cutting tools attached to a frame by a shank. Most are rear-mounted. Provide better results when used before weeds have more than four leaves. Cuts off plants between rows, and moves soil into the rows, smothering small weeds. Controls weeds between rows, but weeds on the row are untouched. Cultivation can be a problem if done too close to the crops, damaging their roots. Corn can have an extensive root system at eight-leaf stage, and cultivation would be too deep and too close to the row, damaging roots. |
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Definition
| A product added to an herbicide's formulation in order to increase its selectivity, protecting the crop. It triggers metabolisms in the plant to make more of the enzyme for the herbicide's degradation, allowing for more rapid detoxification. It does not bring the crop back to the health it would be at in an herbicide-free state, but it does reduce crop injury considerably. The safener should work for the crop only, and not the weeds. |
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Definition
| An inundative biological control used for dandelions in turf in Canada. Failed shortly after reaching market. The product worked too well, and it completely eliminated the weed, also eliminating demand for the product. The sclerotia of a fungus are mixed into pellets which are applied to the centre of the dandelion with a spring-loaded stick. Application is not easy. Attacks only broadleaf plants. Uses an acid to degrade the cell wall, which grasses can resist. Has limited success. Named after the Greek god of agriculture and harvest. |
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Definition
Tripleurospermum inodorum
Family Asteraceae. Can be a biennial. Cotyledons resemble those of ragweed. Its first two leaves are divided into 4 - 5 lobes. Mature leaves are divided, hairless, and finger-like. Flowers are white and daisy-like, resembling those of ox-eye daisy. Has a strong root system.
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Term
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Definition
| Conventional tillage operations that work the soil to a depth less than 15 cm. Depending on timing and type of implement used, its aim is to control weeds or to smooth and level the ground prior to planting. Done with cultivators, discs, harrows, or roto-tillers. Organic farmers use blind-harrowing in cereals. Can be used to work the soil prior to planting, to let weed seeds germinate for a few weeks; the soil is then worked again at planting; works well for annuals such as wild oats in barley. Its main inconvenience is that it delays planting, which is important in achieving high yield. After germination, but before crop emergence, the field is harrowed. Small weeds that have already emerged are pulled out. Should not be used on under-seeded cereals. |
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Definition
| A type of fire and heat control. Uses propane burners that allow for selective weed control when plants are tall enough. Burners are mounted on a toolbar and may be combined with inter-row cultivators. Began in the 1950s in corn and cotton, but was made obsolete by herbicides. In cotton, done when plants are 20 cm, with flames directed towards the base of the plant. In corn, done on the row in pre-emergence, and on coleoptiles until the first leaf is up. Then at six-leaf stage or afterwards, the flame is directed under the foliage. It is not the flames which burn the weeds, but the heat that causes cell contents to expand and break the cell wall. If plants are burning, you've done too much. Costs depends on the price of propane, which can be variable. Requires 5 gallons of propane per acre. Availability of equipment is an issue. Not as cost efficient as atrazine metolachlor, the standard herbicide in corn. Very efficient against annual broadleaves, but lets greasses and perennials escape. Advantages include: no chemicals, row or broadcast, and can be selective. Disadvantages include: no effect on grasses, non-residual, damages crop if maladjusted, and requires specialized equipment. |
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Term
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Definition
| An important characteristic of herbicides. Ability to kill only the weeds, and not the crop. Can be discovered by accident, and must be tested. Most selectivity is conferred by differences in metabolic degradation of the herbicide. |
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Term
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Definition
| A factor which can affect the retention of an herbicide. There must be enough foliage to intercept adequate herbicide to kill the plant. Freshly mowed weeds or newly emerged perennials don't have enough leaf material to retain adequate amounts of herbicides. |
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Definition
Senna obtusifolia
Family Fabaceae. Chemical control is more effective when sprayed in the morning, for unclear reasons.
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Definition
| A book by Rachel Carson. Expresses concern about pesticide products and their effects on non-target organisms. Caused a reaction in the 1960s. |
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Definition
| An herbicide which allows for selective control of most weeds in corn or sorghum. Introduced in 1956. Systemic, and xylem-mobile. |
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Definition
| A way that phloem-mobile herbicides may enter the phloem.. The herbicide partitions into the lipid membrane, diffuses across the membrane, and is transferred inside the phloem. The more lipid-soluble the herbicide, the more rapid entry is. |
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Definition
| Plant parts where there is high demand for assimilates. Areas of active growth, such as young shoot tips or roots, food storage such as roots or rhizomes, fruits, and flowers. The phloem brings photosynthates to these tissues, as well as phloem-mobile herbicides. A mature leaf can be turned into a sink by wrapping it in aluminum foil, or by applying artificial hormones. |
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Definition
Chondrilla juncea
Family Asteraceae. A successful case of classical biological control with a pathogen. It was controlled with a rust in Australia. The plant was introduced from Europe, and became a problem in pastures and cereal fields. Strains of rust were introduced, and were very effective, reducing populations considerably. Unfortunately, there were three forms of the species (narrow-, intermediate-, and broadleaf-skeleton weed), and the rust was active only against the narrow-leaf form, allowing the other two forms to take over. In this case the specificity, which is normally a good quality in a biological control agent, was too much.
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Term
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Definition
| Enters plants through the root, coleoptile, or hypocotyl, either through soil water, or when roots grow into the soil zone containing the herbicide. Must be in the soil water solution to be available to plants. May be taken up by germinating seeds, or by shoots and roots of seedlings prior to emergence. No herbicide will kill a dormant seed, except soil sterilants like methyl bromide. Depth of incorporation should be adjusted to where the weeds are. Rate is often determined by soil type. High clay or organic matter soils require a higher rate. In coarse-textured soils, herbicide should have good crop tolerance, a post application, or variable rate application technology. Effectiveness depends on: herbicide moving in the soil, from rain, irrigation, or cultivation; herbicides coming into contact with weeds that are germinating and emerging; and moisture being present for the herbicide to enter the weeds. There is reduced, or zero activity when applied to a dry soil surface. The herbicide can have movement in the soil (volatilization and leaching). Can enter the groundwater. |
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Term
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Definition
| A factor which can affect the persistence of an herbicide. Includes soil moisture, pH, organic matter, type, temperature, and microbial activity. |
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Term
| Soil-herbicide interaction |
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Definition
| Several biological and physiochemical factors control the interaction between soil and herbicides, including adsorption, movement, and degradation. Important for the efficacy of PRE and PPI herbicides. |
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Term
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Definition
Nightshade family
A family of plants. Includes climbing nightshade, eastern black nightshade, tomato, potato, petunias, eggplant, and peppers, including spicy peppers. |
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Term
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Definition
| Putting down clear plastic on the soil has a greenhouse effect which increases soil temperature. Can be used to speed up germination of seeds to take advantage of early markets. Used in warm countries such as the USA to clean the soil. Extended solarisation kills weed seeds, fungi, insects, and nematodes. |
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Definition
| Plant parts with high supply of assimilates. Includes expanded, photosynthesizing leaves, and rhizomes and storage organs. |
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Definition
Sonchus sp.
Family Asteraceae. Germination is reduced to zero of mowed before bud stage.
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Term
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Definition
| A type of in-row weeding implement. Uproots weeds. Displaces weeds and small soil colloids, breaking the soil crust on the row. |
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Definition
Sonchus asper
Family Asteraceae. Has shiny, waxy leaves with two rounded lobes that attach to the stem.
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Definition
| The first step of herbicide action. A process that an herbicide must go through to be effective. The amount of spray intercepted by the foliage depends on the leaf, and spray factors. Leaf angle can be critical; plants with more erect leaves (grasses) intercept less spray than plants with leaves parallel to the soil (broadleaves). Some plants may have drooping of the leaves at night, and this should be considered when timing sprays. Droplet size affects interception; large droplets may bounce off leaves and break into smaller droplets, or fall to the ground. |
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Definition
| A factor which can affect the retention of an herbicide. There must be enough volume (L/ha) to penetrate the canopy and give good coverage. If volume is too high, there may be runoff of herbicide. Better coverage is needed for contact herbicides than systemic herbicides. |
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Definition
| A type of in-row weeding implement. Uproots weeds. Flexes vertically and horizontally. |
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Definition
| A type of in-row weeding implement. Can be set so that they move soil away from the row, or move int onto the row, covering up small seedlings. |
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Definition
Hypericum perforatum
Family Hypericaceae. A perennial weed native to Europe. It was probably introduced by accident. First reported in western USA in 1900. Spread into rangeland where it was favoured by overgrazing, and became abundant. Not as widespread in Ontario. Contains a toxin that affects the central nervous system of sheep and cattle, making skin photosensitive, and reducing appetite. The animals get sunburns at low radiation levels. It was controlled using classical biological control in the 1940s, introducing Chrysolina beetles. Has medicinal properties, and may be cultivated in fields which Chrysolina beetles are a pest! A "goldmine" of compounds. Has antidepressant effects. Usually grown organically, because it is a natural remedy.
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Term
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Definition
| When an herbicide disrupts a metabolic process so that the plant runs out of an essential product. The plant eventually runs out and dies. Symptomology is delayed because the molecule may run out slowly. |
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Definition
| A type of fire and heat control. Sterilization of the soil, giving general control of weed seeds, soil insects, nematodes, and some diseases. Needs to be done to all soil in a greenhouse, however weeds may still enter through air vents. |
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Definition
| Can be controlled with Devine. An extension agent noticed a pathogen growing on the weed, and produced Devine from it. |
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Definition
| Used in 1930 to kill broadleaf weeds in cereals. A strong acid. It burns the leaves, but the crop's growing point is protected. It was cost-effective and speedy compared to other methods of weed control at the time. |
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Definition
| A safener which may be added to Puma to increase oxidation of the herbicide in the crop, reducing crop injury. |
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Definition
| The continuous system of living cells in a plant, connected by plasmodesmata. Includes the interconnected phloem. A living system. pH is 7.5. |
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Definition
| Technology developed in Warwick, UK. Uses a drill planting pattern and artificial vision guidance. A half-moon shaped blade rotates around each plant for in-row cultivation. |
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Definition
| An herbicide which has tranlocation within the plant, by phloem or xylem. It moves and distributes throughout the plant. It is better than contact herbicides, spreading to new growth. It can spread to neighboring plants through rhizomes or stolons. Selectivity is crucial. |
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Term
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Definition
Tanacetum vulgare
Family Asteraceae. Has a main stem which resembles a feather. As leaves mature, they become wider and broader in comparison to ragweed. Leaves smell like Vick's vapo-rub!
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Definition
Jacobaea vulgaris
Family Asteraceae. Flowers are more separated than those of tansy, and leaves are scentless. There has been research in North America for classical biological control.
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Definition
Mode of action
The sixth step of herbicide action. The metabolic processes (enzymes) that an herbicide must stop to kill the plant. In order to do this, there must be enough herbicide in the cell to stop the target. Herbicides from the same chemical family have the same target site. Sometimes there is more than one herbicide chemical group that attacks the same target. The herbicide acts as an enzyme inhibitor. The reaction inhibited is essential, and cannot be compensated by any other reaction. The metabolic pathway is disturbed, and the plant dies from starvation and/or accumulation. Many herbicides target steps in photosynthesis, since non-plant organisms are not affected. |
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Definition
Dipsacus fullonum
Family Asteraceae. Found on roadsides, pastures, and no-till systems. Spends a few years as a rosette. Has thick, spiny leaves. When it bolts, it has spiny stems and grows to 50 cm in height. Flowers are blue-purple. Has a large, cone-shaped, very spiny fruit.
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Definition
| An herbicide. Used at a rate of 10 - 18 g active/ha. Introduced in 1983. |
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Definition
| Family Asteraceae. May be controlled with calcium sulfate. |
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Definition
| A fish used as a biological control agent to control algae in Africa. |
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Definition
| A form of mechanical control. Done mainly to control weeds, but also to prepare seedbeds to facilitate crop emergence, and sometimes to incorporate pre-plant herbicides. Has a big effect on weeds. Seeds are buried. Resets the succession process. Row crop planting has been developed to allow for tillage between rows. Works because many crops don't need the entire growing season: this allows some tillage work in the off-season. Tillage can be broken down into conventional and alternate systems: conventional tillage is at one end of a scale, and zero-tillage is at the other, with alternate systems in between. Use of herbicides has lessened dependence on tillage for weed control. Tillage equipment specifically designed for weed control include the rotary hoe and row crop cultivator. |
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Definition
Linaria vulgaris
Butter-and-eggs
Family Plantaginaceae. A creeping perennial. Found mostly on roadsides, pastures, and strawberries in late years. Has vegetative propagation with rhizomes, which bud at regular intervals. Leaves resemble those of flax. It is a pretty plant with nice flowers that resemble snapdragons. People are sometimes surprised that it is a weed. Has the capacity to be very invasive. Seeds germinate at 1 - 2 cm deep.
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Definition
Nicotiana tabacum
Family Solanaceae. Can be used as an insecticide at high doses.
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Definition
Solanum lycopersicum
Family Solanaceae. When they were introduced to Europe from South America, they were thought to be poisonous because many Solanaceae weeds in Europe have poisonous fruits. It took people a while to adopt them.
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Term
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Definition
| A type of in-row weeding implement. Uproots weeds. Flexes vertically and horizontally. |
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Definition
Pro-herbicide
A metabolic process where an herbicide is converted into its active form after it enters the plant cell. The active form does not efficiently get into the cell, and would be ineffective as a product. |
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Definition
| The fourth step of herbicide action. A process that an herbicide must go through to be effective. Once in the plant, the herbicide must move to the site of action. Herbicides may be xylem-mobile or phloem-mobile. Conditions which promote transpiration increase movement of herbicides from roots to aerial parts, including high temperature, irradiance, and soil moisture, and low air humidity. Extreme conditions can have the opposite effect; very high temperature induces stomatal closure, reducing upward movement of herbicides. Does not occur for contact herbicides. |
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Definition
| A soil-applied herbicide which is normally safe in tomatoes. If planting is too shallow, more is absorbed by the roots and there can be crop damage. |
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Definition
| An herbicide. Introduced in 1981. Used at a rate of 15 - 30 g active/ha. |
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Definition
Treflan
A soil-applied herbicide which must be immediately incorporated mechanically due to high volatility. |
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Definition
Family Loranthaceae. A parasitic plant.
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Term
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Definition
| A large storage organelle in plant cells. Conjugates of herbicides may be stored in the vacuole. Toxins are stored within it, allowing the plant cell to keep living. |
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Definition
| The USA was on the side of South Vietnam, fighting communist North Vietnam because they were allied with the Russians. The USA army had lots of large artillery, which is difficult to use in the jungle. Defoliant herbicides were sprayed onto the jungles, including Agent Orange. |
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Definition
| An herbicide formulation containing systemic and contact herbicides. It had an ad campaign that involved attractive ladies, but it as not a very good herbicide. |
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Term
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Definition
| A factor which affects the retention of an herbicide. After the water evaporates from the formulation, the herbicide vaporizes and is lost. Some herbicides are more volatile than others. Losses are increased by higher temperatures and wind. |
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Term
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Definition
| Changing from a solid or a liquid into a gas. A form of movement of herbicide in the soil. The herbicide is lost to the air, blowing away into the atmosphere. It evens out an herbicide in the soil. Herbicides differ in their volatility. Losses are greater under higher temperatures, and in sandy soils because it is more porous. Herbicides with high volatility require soil incorporation. Negative effects include: loss of weed control, and vapour drift that can cause injury to non-target plants. |
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Term
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Definition
| Molecules with a carboxylic acid group. Makes herbicides likely to be phloem-mobile. Accumulate in the phloem because pH within the symplast is 7.5, and the pH in the apoplast is 5.5. In the apoplast, the weak acid is protonated, changing its properties to make it more soluble in lipids, allowing it to flow through the plasma membrane. It diffuses into the phloem, where the pH change leads to deprotonation. The weak acid is now stuck inside the phloem, and accumulates there. |
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Term
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Definition
Daucus carota
Bird's nest
Queen Anne's lace
Family Apiaceae. It is the same species as domestic carrot. The vegetative part looks the same, but the root is different: it is white, narrow, and fibrous. Germinates in September, and overwinters as a rosette. In the spring it bolts, and reproduces. Grows to 20 - 100 cm tall. The inflorescence is an umbel of small white flowers, with one red flower in the centre. The name "Queen Anne's lace" refers to the lace-like appearance of the inflorescence, and the red flower: it may be the blood from a pinprick while Queen Anne was sewing lace, or it may refer to the blood of Anne Boleyn, a queen who was beheaded.
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Definition
Sinapis arvensis
Family Brassicaceae. It may be difficult to control with chemical control in canola, because they are closely related.
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Definition
Avena sp.
Family Poaceae. A weed which is too similar to domestic oats to be controlled with classical biological control. May be controlled using Achieve.
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Definition
Striga sp.
Family Orobanchaceae. A hemiparasitic plant. Once the flower emerges, the damage to the crop is already done, since damage occurs underground. You can use plants that trigger germination, or use a low value cash crop. Affects C4 plants, including foxtail and corn. Connects to the xylem of the host plant. There was an outbreak in North and South Carolina in the USA. Includes S. hermonthica and S. asiatica. Costs $250 million over a 50-year period.
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Definition
| Transports water from roots to shoots. Water goes up the tubes using surface tension. As water transpires from leaves, it pulls water up the xylem. It is easier for herbicide to enter the xylem than the phloem. |
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Term
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Definition
| An herbicide which moves upward through the xylem with water flow. Older leaves are affected first. Applied to the soil. If applied to leaves, cannot move into the roots. Movement is a function of water potential, driven by transpiration. Herbicides in the apoplast move from regions of high water potential to regions of low water potential. In most cases movement is from roots to shoots. Herbicides eventually move into the symplast, and accumulate in organelles in which they have no herbicidal action. |
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Definition
Achillea millefolium
Family Asteraceae. It can be controlled by geese and turkeys in strawberries: they eat the weed.
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Definition
Rhinanthus minor
Family Orobanchaceae. A hemiparasitic plant.
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