Weed Management

Weed Management Evonne Gong

For information on managing weeds in specific crops, use the search bar or see the appropriate crop section(s).

Weeds compete with crops for water, light, and nutrients thereby reducing crop yield and quality. Competitive effects of weeds are density dependent, with increasing weed density causing increasing crop yield loss. The magnitude of loss varies based on the crop and weed species present and the timing of competitive interactions. Carrots, beets, and alliums, for example, are small-seeded, slow to emerge, and are poorly competitive early in the growing season. Larger-seeded crops (e.g. pea, bean, and corn), tubers (potato), or transplanted crops start with a significant initial size advantage over germinating weeds. A first principle of weed management is to establish this size advantage, and then maintain it with early weeding or mulching to reduce the density of competition weeds. To this end, successful weed management requires good foundational agronomic and horticultural practices regarding seedbed preparation, fertility and moisture management, timing and density of planting, choice of variety, as well as necessary early management of insect pests and plant pathogens. Remember, in plant competition, “the big get bigger!”

Weed Biology and Ecology

Weed identification is now easier than ever, with apps like “Picture This” getting better every year. While apps still perform poorly in identifying grasses and weed seedlings, recognizing your mature weedy flora is a great place to start. Weeds of the Northeast by Uva, Neal, and DiTomaso is another useful reference for weed identification.

Weedy plant species often share certain traits or characteristics that contribute to their success as the early colonists of disturbed sites, which is after all, the ecological job or “niche” of a weed. Fundamental weedy traits include rapid growth, high amount of seed production, and most notably, seed/bud dormancy to ensure offspring germinate and attempt to grow over several future years—an impressive bet-hedging strategy. Weedy species are also known for their “plasticity”, in other words, genotypic flexibility whereby an individual may exhibit different morphology in response to its environment (e.g., bushy growth in full sun but erect growth in a dense crop). 

Annual plants complete their life cycle in one year: seeds germinate, seedlings grow to maturity, flower, and reproduce all within a single growing season. Winter annuals germinate in late summer or fall, overwinter, and set seed the following spring. Summer annuals germinate in spring or early summer and set seed before fall, often in response to shorter days. Timing of germination and thus emergence is affected by species-specific dormancy characteristics and environmental conditions including light quality (e.g., affecting phytochrome), temperature, moisture, gas exchange, nitrate, and many other factors. These in turn are dramatically affected by soil disturbance (tillage or cultivation). Thus, it should be no surprise that annual weeds dominate the weedy flora of vegetable farms that rely on soil disturbance for residue management, seedbed preparation, amendment incorporation, and weed control. 

Weed seedbanks vary widely across farms. The seedbank refers to weed seeds on the soil surface or buried in the soil. Generally, seedbanks are larger on organic farms compared to farms using herbicides. Larger seedbanks result in a higher density of weed seedlings, or greater “weed pressure” as described by some farmers. The “bank” metaphor is useful in thinking about management, specifically the aim to reduce “credits” to the bank, i.e., avoid or reduce weed seed rain, while encouraging “debits” or losses. A common misperception is that weed seeds last forever in the soil, so “why bother to manage the seedbank?” While it is true that a seed may occasionally last many years, perhaps decades, by far, most seeds germinate or die in the first year. In fact, many annual weed seeds have a half-life of less than one year. In other words, 50% of the seeds produced this season will be gone in less than a year. This is true for several important weeds in our region, including redroot pigweed, common lambsquarters, hairy galinsoga, yellow foxtail, and crabgrasses.

Vegetable farmers are fortunate in having many options for weed seedbank management. Consider a field that will be used for a sequence of short season crops like radishes or leafy greens. Shallow tillage for seedbed preparation in this case serves to encourage weed germination, the most important of seedbank debiting mechanisms. This way, crop harvest can be completed and residues incorporated before weeds mature, thus preempting seed rain. 

Emergence periodicity is a useful aspect of weed biology that can be used to optimize fallowing or stale seedbed events that aim to reduce the germinable weed seedbank. Shallow tillage breaks seasonal dormancy for species ready to germinate. Thus, if targeting summer annuals, shallow tillage in June or July will encourage germination, while winter annual species will remain in the seedbank. 

Perennial weeds can live for more than one year and while most produce seed, vegetative propagation by stolons, rhizomes, or roots is generally more important. Tillage operations often drag perennial weed fragments from sod headlands or farm roads into vegetable fields. Shallow tillage around field margins throughout the growing season can establish a fallow zone to avoid this dispersal from tillage.

Monitoring weeds is an important but often neglected part of a weed management plan. Weed maps of field areas are extremely helpful in planning weed control strategies. A weed map can illustrate problem areas so that growers can target specific problems in specific areas and help plan for future crop rotations. Over time, weed maps can show shifts in weed pressure and indicate the possible need for a strategy change. Maps can also highlight the importance of managing dispersal, e.g., avoiding tillage that drags quackgrass rhizomes from grass alleys into fields, or working around a weed patch to avoid tillage dispersal. 

Dispersal is critical to the success of weeds, but rarely a priority for management. It is widely thought that weed seeds are blowing in from neighbors, hitching rides from birds or mammals, or washing in with irrigation or surface waters. These are important dispersal mechanisms, but they are rare events, generally moving only a very small fraction of a batch of seeds. In fact, well over half of most seeds are dispersed right around the base of the mother plant, and most remaining seeds not much further. In a natural setting, these seeds would be very crowded, with intense competition among the weeds when a cohort germinates the following year. In a farmed system, however, tillage events serve to disperse the seeds, spreading them out to the benefit of the weed. These local dispersal factors drive the patch dynamics that will be evident in your weed maps, with dense areas where reproduction was high, lower density radiating from the patch where tillage moved seeds, and then many other locations where weeds may be absent. 
 

Physical Weed Management

Physical Weed Management Evonne Gong

Physical weed control refers to actions that remove or kill weed seedlings, aiming to reduce weed density and thus maximize crop yield and quality. In vegetable crops, this often includes hand weeding, which is effective but expensive. Hand weeding time/cost is dependent on weed density, so efforts to reduce the weed seedbank and increase the efficacy of weeding tools will often improve net returns. The availability and cost of labor are key considerations, although it is common to perform some hand weeding in almost all vegetable crops. When relying on hand labor, start weeding operations with wheel hoes that can cover a lot of area quickly no matter the weed density. Next move to long-handled hoes designed for weeding: notable favorites among veteran organic vegetable farmers include the Glaser stirrup hoe and the colinear hoe. Using tools to get as close to the crop row as possible will reduce the final hand weeding labor. When tools are used for weed removal, physical weed control is sometimes referred to as “mechanical weed control”, or simply “cultivation”.

Cultivation is an important component of weed control in vegetables. Efficacy or effectiveness, refers to the proportion or percentage of weeds that are killed. A central problem with cultivation is that efficacy is low (60% is common) and highly variable (some places in the field may have 95% efficacy, while another may have only 5%). To improve efficacy, there are several principles to keep in mind.

  1. Establish and then maintain the crops’ size advantage. Selectivity (which refers to killing weeds but not the crop) of cultivation tools are generally based on a size differential between the crop and weed.
  2. Cultivation is most critical early in the growing season. Weeds are most effectively cultivated shortly after they germinate, and crops are most sensitive to weed pressure during their early stages of growth.
  3. Carefully prepare the seedbed. Flat, firm, residue-free soil surface conditions will allow weeding tools to consistently function throughout the field. A light-weight field cultivator or soil conditioner with a rolling basket is often a good choice. While large-seeded or transplanted crops do not require a perfect seedbed for planting and stand establishment, later cultivation operations will benefit from these early season efforts to prepare a nice seedbed.
  4. Tools should be carefully adjusted, first in the shop, and then in the field after some testing. Row-crop tools should target the same number of rows that were planted, or a simple fraction of this. For example, if using a one-row seeder, plan to cultivate one row at a time. If planting two or four rows, use a two or four row cultivator. Seeding with a walk-behind seeder is generally not going to be suitable for later tractor-mounted cultivation tools.
  5. Tools should be adjusted to work as shallowly as possible to minimize movement of seeds in the seedbank and break seed dormancy. After carefully adjusting spacing, place a 3/4" thick board under the gauge wheel of parallel linkage units (depth-controlling units), and then drop tools to the floor and tighten. Mark lines on the shop floor indicating crop row spacing to allow precise adjustment relative to the row. Magnetic levels are handy to adjust top-linkage of three-point hitch tools, and a protractor can be used to check the angles of tools to either avoid soil movement or hill as desired.

Blind cultivation is performed after crops have been planted, over the top of them, so that both in-row and between-row areas are cultivated. To minimize crop damage, this should be done before the crop has emerged and/or once it is well rooted. Slightly deeper planting depths and slightly higher plant populations are recommended to compensate for some crop loss that may occur. Very tender crops such as leafy greens are not amenable to this technique, but a surprising array of crops are suitable for blind cultivation, including corn, cucurbits, and beets, depending on stage of growth and equipment used.

Tine harrows have multiple rows of flexible metal tines that cover the entire soil surface, wiggling slightly as they are pulled along, uprooting or dislodging very small weeds. They work best at relatively high speeds, and the wide span of the tool makes cultivation quick. They are rear-mounted and available in many widths. The tension on the tines can be adjusted on some units or by the pressure on the 3-point hitch on other units. Gauge wheels can be used to maintain uniform depth. Tine harrows work best in friable soils free of rocks, and when weather allows weeds to dry out on soil surface after uprooting.

Rotary hoes have many narrowly spaced metal wheels each with about 16 curved teeth that work the surface of the soil. Used within the first few weeks of planting vigorous crops like corn or beans, they destroy weeds that have just germinated. Ground-driven, spring-loaded wheels do little damage to the crop and work well at high speeds on dry, rock-free soils with little residue. They are rear mounted and available in many widths. The teeth, or spoons, lose their effectiveness if not sharp.

Between-row cultivation can be performed with varying degrees of aggressiveness, so that soil may or may not be pushed into the row to obtain some in-row weed control. Commonly used cultivation setups consist of a shank (either straight, C-, or S-shaped) attached to a toolbar, with a cultivating tool (shovel, sweep, knife, hilling disc, etc.) attached to the bottom. The more curve to the shank, the more it will vibrate and flex in the soil. Trip-shanks have a release mechanism that allows the shank to pop up when it hits a rock. Shanks can be arranged on multiple toolbars to offer complete coverage between multiple rows in beds. There are many kinds of tools that can be attached to the shanks, and these should be selected to disturb only as much soil as is needed to kill the weeds present. In general, one starts the season with smaller, shallower tools to kill small weeds when the crop is small; as the season goes on, if larger weeds are present, then more aggressive tools are needed. As the crop grows it is possible to more aggressively push soil into the row without causing damage. For example, shovels might be followed by sweeps and then hilling discs. Another strategy is to adjust the angle of cultivating tools such as hilling discs or rolling cultivators as the season goes on. Start by pulling soil away from the row when cultivating a young crop; that creates a small hill that can be pushed back into the row when the crop is a bit older to bury weeds.
In small and/or tender crops like leafy greens, shallow tools are needed that will not move soil into the row and cause damage. A side-knife (or beet-hoe) may be used to cultivate horizontally next to the crop, just below the surface.

Basket weeders are relatively high-speed, between-row cultivators good for control of small weeds in narrow rows when crop is small. The wire baskets work the soil surface and do not move soil into the row, but they don't work well in crusted or rocky soil. The front set of baskets are ground driven, and they turn the rear set of baskets a bit faster via a chain and gearing, causing scuffing of the soil. These are available in 2-6-row units that can be rear- or belly-mounted.

Finger weeders consist of steel cone wheels that are ground-driven by spike tines on the bottom, with rubber fingers on the perimeter. The rubber fingers work the soil just below the surface, uprooting small weeds located very close to the crop. Finger weeders work best for control of small weeds in dry, friable soil with few rocks or residues. Clay soils may stick to fingers.

Spring-hoe, torsion weeders, and spyder weeders are flexible blades and square metal stock that disturb soil around the base of plants, and ground-driven spyder wheels with staggered teeth in an uneven pattern that break clods and throws soil into row, or pull it away, depending on the angle. These can be toolbar-mounted, either under the belly or in the rear. They can be used together, separately, or in conjunction with other cultivators.

Rolling cultivators have gangs of soil-driven 'spider wheels' that mount independently on a toolbar. The angle that they work the soil, and thus their aggressiveness, is usually adjustable. The number of gangs grouped together determines cultivator width, and these are usually rear-mounted, but pairs of gangs may be belly-mounted to work a row or two. Soil can be thrown into row to bury small weeds or to form hills, depending on angle of the gangs. This is a relatively heavy, aggressive tool.

Reigi weeders require a rear operator who steers a pair of rotating horizontal wheels in and out of the crop row. The wheels are turned by a PTO-driven belt, and they have stiff tines on them that root out weeds. The wheels come in several sizes useful for various row spacings, and the units come in 1- or 2-row models. These are very effective for killing weeds in and next to the row in widely spaced crops like pumpkins, first-year strawberries, or sweet corn with a lot of skips.

Flame weeding, also known as thermal weeding or flame cultivation, exposes plants to brief periods of high temperature that causes the water in the plant tissue to expand rapidly, rupturing plant cells and leading to tissue damage. Plants are not burned or incinerated, but "blanched". They will not show symptoms of injury until several hours after exposure. Some weeds, such as purslane, can tolerate high temperature, and grasses with their growing points below ground are not controlled by flaming. When weeds are moist from rain or dew, more heat (i.e., a slower tractor or walking speed) will be necessary.

Flaming is ideal for stale seedbeds because it kills weeds without soil disturbance, which would bring up new weed seeds to germinate. For longer-lasting weed control, apply the final flaming as late as possible prior to crop emergence after seeding or just prior to transplanting. However, broadleaf weeds should be flamed at the three-leaf stage, before they grow too large for effective flame control.

Hand-held propane torches are commonly used to flame single rows at a time, but multi-row bed-flamers and tractor-mounted flamer kits are also available. Larger units require greater attention to safety during construction and operation. Safety is a big issue with flaming. Consult with a gas professional if constructing your own flaming unit. Do not mount propane tanks intended for stationary use onto tractors. Flame against the breeze and avoid areas with dry residues or dry hedgerows. Liability concerns may hinder the use of flaming.

Cultural Weed Management

Cultural Weed Management Evonne Gong

Plant competition is a foundation of weed management. Remember, “the big get bigger.” Large-seeded crops and transplants have an initial size advantage over weeds. Decreasing the space between crops will also increase soil shading. Overall, the more rapidly a crop can cover the soil ahead of weed emergence, the more competitive that crop will be. Choose high quality seed, calibrate equipment to ensure accurate seeding rates and depth, and where possible, supply resources selectively to the crop, e.g., apply fertilizers banded below/near the crop row, or through drip irrigation, instead of broadcasting.

Other cultural strategies that help to manage weeds include cover crops, mulches, fallowing, stale beds, crop rotation, and soil preparation.

Cover crops

Cover crops reduce overall weed populations in several ways.

  • Shallow tillage between short cycles of cover crop growth kills weed seedlings and encourages germination of a new “flush” of weeds that can be killed with the next disturbance. Encouraging weed seed germination, but not allowing further weed seed production reduces weed seeds in the soil seedbank over time.
  • While it is growing, a dense cover crop stand will suppress weed growth by shading the soil. A season-long cover crop can help suppress weeds that may have otherwise matured and set seed.
  • Cover crops can slow soil warming in the spring, helping to slow weed seed germination and reduce the soil seedbank over time.

Despite these benefits, perennial weeds can increase when perennial cover crops are in place for a longer period of time, e.g., one or more years of red clover.

Mulches

Mulches are often used to control weeds. Mulches can be organic (straw, hay, grass clippings, dead cover crops), inorganic (plastic), or degradable (bio- or photo-degradable plastics).

  • Organic mulches are effective if they are thick enough to keep weeds from emerging through them (usually at least 2-3"). Downsides of organic mulches are that they can be expensive, they reduce soil temperatures and slow soil warming, they can reduce nitrogen availability, and they can harbor animal pests. Cooler soil temperatures can be a problem in warm season crops. It is recommended that the mulch application be delayed enough to allow the soil to warm up sufficiently for the crop.
  • Black plastic mulches will warm soil and eliminate weed pressure. However, weeds emerging through the planting holes and between strips of plastic mulch can still reduce yields if not controlled. Infra-Red Transmitting (IRT) mulches are less effective than black plastic for controlling weeds, and clear mulches can enhance weed growth. Some growers plant cover crops between plastic mulch strips as "living mulch", but these cover crops can also compete with the crop. Killing the living mulch before the crop is planted, mowing the mulch on a regular basis, or using raised beds will help to reduce but not eliminate competition. See the section on Herbicides and Plastic Mulches for more information. A downside of black plastic mulch is that they generate a lot of plastic waste material, which can be difficult and expensive to dispose of.
  • Degradable plastic mulches are more expensive than plastic mulches and rip more easily, which exposes soil where weeds can germinate. They are also not approved for organic production. However, degradable plastics can be plowed into the soil after the growing season, reducing the need for plastic waste disposal.

Fallowing

Fallowing is not planting a field with the intention to reduce weed seed populations. Repeated shallow soil disturbance will encourage weeds to germinate while subsequent events kill seedlings before they go to seed. Over time this strategy will reduce the weed seedbank of a field and can help manage established perennial weeds.

Crop rotation

Crop rotation can be a tool for managing weeds. Weed species present tend to be most like the crop planted. Examples include grasses in corn, winter annuals with early-planted crops, and perennial weeds with perennial crops. Rotating crops among these groups will tend to disrupt this trend.

Proper soil preparation

Proper soil preparation can influence weed emergence. Soils which are rough and less firmly packed will yield fewer weeds than those that are more finely worked, more compacted, and more uniformly moist. However, as noted above, a well-prepared seedbed will help weeding tools function to their potential during later cultivation events.

Stale seedbed

Stale seedbed is the practice of preparing a field for planting and then lightly disturbing the soil on a regular basis to kill small weeds as they emerge, without bringing up new weed seeds from below the top few inches of soil. Tools that can be used for this practice include chain-drag, spring-tooth harrow, light-weight disc harrows, tine weeders, or flame weeders. Stale seedbeds can be used in the spring before a crop is sown, or in the summer after a spring crop but before a fall crop. A summer fallow works better on summer annual broadleaves that emerge later in the season. Perennial weeds may be weakened but not killed. See Stale Seedbed Technique for more information.

Stale Seedbed Technique

The stale seedbed approach involves preparing the soil as if for planting, without actually planting the crop. After soils are prepared, weed seeds in the upper 1-2" of the soil are encouraged to germinate through adequate soil moisture and temperature (with irrigation or row covers). Generally, this happens within 2 weeks. Weeds are then killed with Gramoxone, Roundup, Scythe, or flaming.

Killing emerged weeds with herbicides or flaming does not disturb the soil, and no new weed seeds will be brought close to the soil surface. After using the stale seedbed technique, care should be taken not to disturb the soil any more than is absolutely necessary during the seeding or transplanting process to minimize the amount of weed seeds that are brought up to the surface to germinate. Preemergence herbicides can be used after a stale seedbed to further reduce germination. Any cultivation performed after should be kept extremely shallow (3/4-1" maximum) so as not to reposition any additional weed seeds.

On sandy, loamy, or high organic matter soils, the soil should not crust and modern seeders should still work satisfactorily. On heavy clay soils, crusting could make this technique unusable.

Stale Seedbed Steps:

  • Prepare the soil as if you are about to seed or transplant. If a soil-incorporated herbicide is used, it must be applied and incorporated at this time. The soil should have good moisture (irrigate with 1/4" of water if necessary).
  • Wait as long as possible to allow weeds to germinate and emerge. Allow weed seedlings to grow to the third-leaf stage, or at least to the first true leaf.
  • If you're using transplants: flame the soil or make an application of Gramoxone, Scythe, Aim, or Roundup (if registered for the crop) to the soil surface before transplanting. Transplant the crop, without dragging any additional soil off the bed, and then apply any preemergence herbicide that you would normally use, to the soil surface.
  • If the crop will be direct-seeded: Gramoxone, Scythe, Aim, or Roundup (if registered for the crop) or flaming may be applied just before or just after seeding (see the label). After seeding, apply any preemergence herbicide that you would normally use to the soil surface. CAUTION: If the crop has already been seeded, be careful that the flaming process does not injure the crop seed or the emerging crop seedling.

Check the current herbicide label and recommendations by crop to determine if Gramoxone, Scythe, Aim, or Roundup is registered for use in that crop. Gramoxone, Scythe, Aim, and flaming will have minimal long-term effect on established perennial weeds. For cucumbers, melons, squash, pumpkin, peppers, and eggplant, Roundup must be applied at least 3 days prior to seeding or transplanting.

In cases where Roundup is registered, it can also be used for control of perennial weeds, such as quackgrass and dock, prior to soil preparation. After application, delay tillage for 3-5 days. There is no residual weed control. See the label for directions.

About Herbicides

About Herbicides Evonne Gong

Herbicides are chemicals designed to control weeds. The use of these materials must be exact for satisfactory results. Proper rate selection, timing of application, activation, and observance of all precautions on the label must be followed to obtain optimum performance. Each herbicide controls certain weed species or families. Therefore, knowledge of the weed species present in the field is essential for good weed control. Once the weeds are identified, select the proper herbicide.

Herbicides can be classified several different ways and understanding what the classifications mean can help you better select the most appropriate herbicide to use for different situations.

Herbicides can be pre-emergent or post-emergent.

  • Preemergence herbicides (PRE) are applied prior to the emergence of weeds. Some need to be incorporated into the soil with tillage (pre-plant incorporated) and others are applied to the soil surface and are sometimes incorporated with irrigation or rainfall (pre-soil-applied). In general, they work by preventing germinating weeds from growing, but some can also act on perennial plants that spread by rhizomes, tubers, and stolons. These herbicides prevent new weeds from emerging, but most will not impact weeds that are already emerged. 
  • Postemergence herbicides (POST) work on actively growing weeds. They can be absorbed by the leaves or roots of the plants, depending on the chemical.

Herbicides can be systemic or contact.

  • Systemic herbicides are absorbed by the plant and move through the plant to the site of action, where the herbicide kills the plant.
  • Contact herbicides only affect the plant tissue they come into contact with. It is especially important to achieve good coverage of weeds when using these herbicides.

Herbicides can be selective or non-selective.

  • Selective herbicides only work to kill certain species or types of plants. Selectivity is usually due to the physiology of the plant and the rate at which an herbicide is applied.
  • Non-selective herbicides kill or injure any plant they come into contact with (as long as the weed has not developed resistance to the herbicide). These types of herbicides are used as burn-down products in situations where it is desirable for all living plant material to be killed.

These different classifications are usually well-defined, but not necessarily always exclusive (e.g. a pre-emergent herbicide can also have some post-emergent activity). The different types of classifications interact together. For example, 2,4-D is a postemergent, systemic, selective herbicide meaning that you apply it to actively growing weeds. It is absorbed by the plant and travels to meristems, causing death by uncontrolled growth, and only affects broadleaf plants (not grasses). Paraquat is another postemergent herbicide, but it is a contact and non-selective herbicide meaning that it is applied to actively growing weeds and kills all plant tissue the spray touches but does not harm tissue that is not sprayed.

Adjuvants are added to a pesticide mixture to improve its effectiveness. They include surfactants, stickers, penetrants, and compatibility agents. Pesticide labels may list specific types of adjuvants that will maximize effectiveness of the pesticide. Be sure to use the proper category of adjuvant if the manufacturer makes a specific recommendation.

When adjuvants are recommended, it is because research has shown that their addition increases efficacy of the herbicide. If the label advocates the usage of an adjuvant, do not omit the adjuvant solely to save money. The most common adjuvants used with herbicides are nonionic surfactants (NIS) and crop oil concentrates (COC) which can consist of petroleum, vegetable, or methylated vegetable or seed oils. They increase penetration of the herbicide through the leaf cuticle.

Herbicides and Crop Rotation Restrictions

Some herbicides can have long-lasting activity. Many herbicides have crop rotation restrictions where they have been applied. For example, Devrinol has a 60-day plantback interval for leafy greens. Check the label of each product for details.

Toxicity of Herbicides

The toxicity of pesticides varies by the active ingredient, concentration of active ingredient, and the formulation of the product (e.g. liquid, powder, etc.). The toxicity of a pesticide is expressed in terms of oral (administered internally) and dermal (applied to the skin) LD50. LD50 is the dosage of poison that kills 50% of test animals (usually rats) with a single application of the pesticide product and is expressed as mg/kg of body weight. The lower the LD50 value, the more toxic the material.

The acute (short-term) toxicity of the formulated product is conveyed on label by a “signal word” stated on the front page. 

DANGER (most dangerous): Pesticide product is highly toxic by at least one route of exposure. It may be corrosive and cause irreversible damage to the skin or eyes. If the product is highly toxic if eaten, absorbed through the skin, or inhaled, then the word “POISON” must also be included in red letters.

WARNING: Pesticide product is moderately toxic if eaten, absorbed through the skin, inhaled, or it causes moderate eye or skin irritation.

CAUTION (least dangerous): Pesticide product is slightly toxic if eaten, absorbed through the skin, inhaled, or it causes slight eye or skin irritation.

General Principles for Safe Use

  • Know the herbicide. Read the label.
  • Check the output of sprayer frequently. See Pesticide Equipment Calibration.
  • Replace worn nozzles. It may be necessary to replace them several times a season if the sprayer is used constantly.
  • Rinse spray equipment immediately after use. Use one sprayer for herbicides and another for insecticides and fungicides.
  • For an overview of herbicide use restrictions, safety concerns, and other information see Tables 28 and 29.
  • For an overview of crops labeled for each herbicide, see Table 30.
  • For an overview of weeds listed as controlled on each label, see Table 31.
  • For limitations and special requirements of the herbicide, refer to the product label (or supplemental label).

Rate Selection

Always check the label to determine the proper rate to apply. For most soil-applied herbicides, knowledge of the type of soil and the percentage organic matter usually determines the rate. Generally, the more clay and/or organic matter present in the soil, the higher the herbicide rate necessary for good weed control. For postemergence herbicides, the type of weed, as well as its size, will usually determine the rate.

Incorporation of Herbicides

Some herbicides must be incorporated into the soil to be effective. Herbicides are incorporated because they are volatile and evaporate into the air if left on the soil surface or they will decompose when exposed to sunlight. Herbicides differ in their incorporation requirements; check the product label for the manufacturer's requirements.

Herbicide Sprayer Systems

  • Select a sprayer and pump that can deliver a volume of 20-50 gallons per acre. Most herbicides are applied at rates of 20-40 gallons of water per acre. Pressures of 20-40 psi at the nozzle are recommended for most herbicides. Higher pressures result in finer droplets and increase the chance for more drift. Lower pressures sometimes cause uneven spray patterns.
  • Use 50-mesh screened filters for nozzles and suction lines.
  • Select 80-73º flat fan nozzles. Because of wear, brass tips used exclusively for applying wettable powders should not be used on more than 30 acres before being replaced. Use stainless steel or hardened stainless steel tips for longer wear. Stainless steel nozzle tips are more than twice the cost of brass tips but last about 20 times longer. Hardened stainless steel tips are only slightly more expensive than stainless steel tips but last three times longer. Ceramic nozzles are the most durable.
  • Calibrate sprayers frequently and check for wear, especially when wettable powders have been used. See Pesticide Equipment Calibration.

Resistance Management

Each herbicide has a mode of action—how and where the chemicals in an herbicide work to kill a target weed. However, through natural random genetic mutations, weeds can develop resistance to a mode of action. Resistance in a weed makes it less sensitive to an herbicide. Since mutations that lead to resistance are genetic, they are inheritable. When an herbicide is used, weeds that are susceptible to an herbicide will be killed, but any with the genetic mutation that makes them less sensitive will survive. These then reproduce and pass on the genes that let them survive the herbicide exposure to their offspring. If the same herbicide is used repeatedly in the same field, over time the predominant genetic form of that weed in that field will be resistant to that herbicide. A higher rate of the same or a similar chemical from the same group usually will not control the weed and these weeds can become extremely difficult to manage.

There are many techniques that can help delay the onset of resistance.

  • Integrate cultural, mechanical, and physical weed control techniques to reduce reliance on chemical tools.
  • Scout fields so that you are aware of what is not controlled.
  • Take steps to control escaped weeds, especially preventing seed set.
  • Good rate selection, spray coverage, and herbicide activation helps do the job right the first time and avoids unnecessary repeat applications. Use the proper size nozzles, the correct angle or orientation, and the right amount of water per acre.
  • Time postemergence applications so that the weeds are at the right stage of growth.

One of the most important ways to slow resistance development and extend the useful life of an effective product is to rotate the use of products with different modes of action. This can be done in several ways:

  • Rotate the type of herbicide used on fields where the same crop is grown year after year.
  • Rotate the crops grown on a field so that different herbicides are used on that field.

Even if herbicides have different active ingredients, they can share the same mode of action. It is very difficult to know which herbicides share a mode of action. To help growers effectively rotate herbicides, international groups have assigned group numbers to herbicides based on the mode of action. The Herbicide Resistance Action Committee (HRAC) and The Weed Science Society of America (WSSA) have developed a harmonized classification system of herbicides using numbers to designate herbicide categories. Herbicides with the same number have the same mode of action. Most labels now come with this group number assigned to them (some have not been updated to the HRAC/WSSA number, but will in the future).

When selecting herbicides to rotate between for resistance management, use the group number as your guide and NOT the product name or active ingredient. These resistance groupings are listed in Table 28.

NOTE: The group number is specific for each type of pesticide (insecticides, herbicides, and fungicides). For example, there is no problem with using material from the herbicide Group 1 and an insecticide or fungicide from Group 1.

The most common weed resistance issue that we have in New England is common lambsquarters that is resistant to atrazine.

Groundwater Concerns

The following herbicides have the potential to impact groundwater due to their chemical characteristics and toxicological profile and have been discussed in the crops sections. Check with your state for restrictions on their use in sensitive areas. For example, Massachusetts has Zone II designations and regulations pertaining to the use of these herbicides in those areas.

  • Atrazine (Aatrex)
  • Bentazon (Basagran)
  • Chlorthal-Dimethyl (Dacthal, DCPA)
  • Dimethanamid (Outlook)
  • Diuron (Karmex)
  • Fluthiacet-methyl (Cadet)
  • Metolachlor (Dual Magnum)
  • Metribuzin
  • Pronamide (Kerb)
  • Simazine (Princep)

Herbicides and Plastic Mulches

With the increased use of plasticulture for the production of various vegetable crops, it is very important to keep in mind a few points for proper weed management. Here are some tips:

If soil is fumigated under plastic strips (e.g. Vapam), there is no need for an herbicide under the plastic. Herbicides can be used under the plastic but are often unnecessary under black plastic unless there is nutsedge or excessive weed pressure. If you use clear or white plastic without soil fumigation, then you need an herbicide under the plastic mulch. To get the best results, take the following steps for herbicide application:

  1. Prepare a pressed bed.
  2. Apply the herbicide to the bed surface.
  3. Activate the herbicide with rainfall or overhead irrigation (at least 1/2"); if the herbicide needs to be mechanically incorporated, do so and repress the bed.
  4. Apply the plastic mulch.
  5. If weeds are present between the plastic strips before planting, use a banded application of Gramoxone plus surfactant, or Roundup (if registered for stale bed use) to kill all existing vegetation. Depending on the level of weed vigor, a second application of Gramoxone plus surfactant may be needed before planting. Do not broadcast apply these herbicides to the surface of the mulch.
  6. For weed control between the plastic beds after planting, use a registered preemergence herbicide for that crop. Do not use nonregistered herbicides between beds as the crop roots will grow in that zone and, in many cases, the crop will be damaged or killed. Do not spray the surface of the plastic with any preemergence herbicides! During a rainfall the excess herbicide will wash into the holes where the crop was planted and will greatly concentrate the herbicide. Thus, the crop will be damaged or killed. When banded applications of herbicides are used, remember to adjust the rate of the herbicide downward to conform to the actual ground area being sprayed (with 30" beds and 30" areas between strips, only half the normal amount of herbicide would be required per acre since only half the amount of soil area per acre is actually being sprayed).

Notes:

  • Herbicide use under row covers can be dangerous, as some may volatilize and cause crop injury when used under plastic mulches or row covers. Some herbicides are prohibited from use under row covers. Be sure to observe any cautions on the product label.
  • Generally, ventilated covers are safer than solid covers or hot caps, from an herbicide injury standpoint. This is especially true with an herbicide that is moderately or highly volatile.
  • Wherever possible, try it on a small scale before you apply it on a large scale.
  • Use caution when spraying Gramoxone with a backpack or hand-held sprayer. Wear rubber boots, gloves, and a mask or respirator. Avoid skin contact with the spray. If contact occurs, immediately rinse the area with water or rub soil on your skin. Soil will help soak up and bind the chemical, preventing its absorption into the skin. Spray when the wind is calm to avoid spray drift. Also, always use a surfactant and plenty of water with Gramoxone for good control.
  • Vapam is not recommended for use in the spring if the plastic is to remain in place. Under the cool soil conditions at this time of year, the soil will not aerate properly and the crop will be damaged. In plasticulture, these materials are best used if the plastic is applied the fall before planting. With all fumigants, be sure to space the injection shanks correctly. The label recommends a 6" spacing with Vapam.
  • Backpack sprayers or modified boom sprayers are often used for herbicide applications in plasticulture systems. Be sure to calibrate them properly and maintain a constant pressure using a pressure gauge, especially on hand-pumped models. Maintaining a constant speed or walking pace is also necessary. Three miles per hour is a good speed (23 seconds per 100').
About Herbicides

Herbicides Alphabetically Listed by Trade Name (Table 28)

Herbicides Alphabetically Listed by Trade Name (Table 28) Evonne Gong
TRADE NAME1 ACTIVE INGREDIENT HRAC2 GROUP REI (hours) ROTATION RESTRICTIONS PRE-SA3 PPI4 POST5 WEEDS & CROPS LABELED
2,4-D Amine 4 2, 4-D 4 48 no no no yes Annual and perennial broadleaf weeds in asparagus and corn
Aatrex 4L* atrazine 5 12 yes yes yes yes Some annual grass and broadleaf weeds in corn
Accent Q nicosulfuron 2 4 yes no no yes Some grasses (including rhizotomous Johnsongrass) and some broadleaf weeds in corn
Aim EC carfentrazone-ethyl 14 12 yes no no yes Broadleaf weeds in corn and cucurbits
Aquesta 4F sulfentrazone 14 12 yes yes yes yes Mostly annual broadleaf weeds and yellow nutsedge in asparagus, beans, brassicas, cucurbits, eggplant, okra, peas, peppers, rhubarb, tomatoes, and turnip
Assure II quizalofop 1 12 yes no no yes Annual and perennial grasses in legumes
Basagran 5L bentazon 6 48 no no no yes Yellow nutsedge (high rate) and select broadleaf weeds in legumes and sweet corn
Broclean bromoxynil 24 24 or 48  no no no yes Broadleaf weeds in bulb crops
Cadet fluthiacet-methyl 14 12 no no no yes Broadleaf weeds in corn (processing sweet corn only)
Callisto mesotrione 27 12 yes yes no yes Yellow nutsedge suppression and broadleaf weeds in corn and asparagus
Caparol 4L prometryn 5 24 or 48  yes yes no yes Some annual grasses and annual broadleaf weeds in carrots, celery, and parsley
Casoron 4G dichlobenil 29 24 yes yes yes no Some annual and perennial grass and broadleaf weeds and yellow nutsedge in rhubarb
Chateau EZ flumioxazin 14 12 yes yes no yes Grasses and many annual and perennial broadleaf weeds in asparagus, legumes, garlic, artichoke, and peppers
Clarity dicamba 4 24 no no no yes Annual, perennial, and biennial broadleaf weeds in asparagus
Clean Slate clopyralid 4 12 yes no no yes Many broadleaf weeds in asparagus, beets, corn, spinach, and turnips
Command 3ME clomazone 13 12 yes yes no no Annual grasses and some broadleaf weeds in pumpkins and peppers
Curbit ethalfluralin 3 24 yes yes no no Many annual grasses and broadleaf weeds in cucurbits
Dacthal Flowable herbicide DCPA EPA issued an emergency order on August 6, 2024 prohibiting all use, distribution, and sale of this product
Devrionol 2-XT napropamide 0 24 yes yes yes no Many grasses and some broadleaf weeds in asparagus, brassicas, and solanaceous crops
Dual Magnum** s-metolachlor 15 24 yes yes yes no Annual grasses, yellow nutsedge, and some broadleaf weeds in corn, potato, pumpkin, and tomato. **Dual Magnum has an indemnified label for use in some crop due to potential for crop injury. Users must agree to a waiver of liability through the Syngenta website to access the labels for these uses.
Eptam EPTC 15 12 no yes yes yes Annual and some perennial grasses, yellow nutsedge, and some broadleaf weeds in beans and potatoes
Evik DF ametryn 5 12 yes no no yes Many annual grass and broadleaf weeds in corn
Fusilade DX fluazifop-p-butyl 1 12 yes no no yes Many grasses in carrots, onions, spinach, and asparagus
Goal 2XL oxyfluorfen 14 24 or 48  yes yes no yes Some grasses and some broadleaf weeds in onions and brassicas
Gramoxone SL 3.0* paraquat 22 12 or 24 no no no yes Non-selective control of annual weeds and suppression of perennial weeds. May be fatal if swallowed or inhaled. Must complete an EPA-approved training every three years (list this at bottom of table).
Impact topramezone 27 12 yes no no yes Some grasses and many broadleaf weeds in corn
Kerb 50-W* pronamide 3 24 yes no yes no Some grass and broadleaf weeds in lettuce
Laudis tembotrione 27 12 yes no no yes Some grasses and many broadleaf weeds in corn
Lorox DF linuron 5 24 or 192 yes yes no yes Grasses and broadleaf weeds in carrots and parsely (has different pre- and post- emergence efficacy)
Matrix SG rimsulfuron 2 4 yes yes yes yes Grasses, yellow nutsedge, and broadleaf weeds in potato
Metribuzin metribuzin 5 12 yes no yes yes Grasses and broadleaf weeds in potatoes and tomatoes
Outlook dimethenamid 15 12 yes yes yes no Many annual grasses, yellow nutsedge, and annual broadleaf weeds in beans, corn, and root vegetables
Poast sethoxydim 1 12 no no no yes Annual and perennial grasses in most vegetables
Prefar 4-E bensulide 0 12 yes yes yes no Annual grasses in many vegetable crops
Princep 4L simazine 5 12 or 48 no yes no no Annual grass and broadleaf weeds in corn
Prowl H2O pendimethalin 3 24 yes yes yes no Annual grasses and some broadleaf weeds in asparagus, corn, peppers, potatoes, garlic, and onions
Quinstar 4L quinclorac 4 12 yes no no yes Some annual and difficult perennial grasses and broadleaf weeds including bindweed and Canada thistle in asparagus and rhubarb
Raptor imazamox 2 4 no no no yes Some grasses, yellow nutsedge suppression, and many broadleaf weeds in legumes
Reflex fomesafen 14 24 yes yes no yes Some grasses and many broadleaf weeds in beans and potatoes. Can only be used every other year.
Reglone diquat 22 24 no no no yes Non-selective control of small annual weeds and suppression of perennial weeds
Ro-Neet cycloate 15 48 no no yes no Some annual and perennial grasses, yellow nutsedge, and broadleaf weeds in beets and spinach
Roundup PowerMax 3 glyphosate 9 4 no no no yes Non-selective. Absorbed by the foliage of all weeds and translocated into the plant. Many formulations are available.
Sandea halosulfuron-methyl 2 12 yes yes no yes Yellow nutsedge and broadleaf weeds in asparagus, beans, corn, cucurbits, and fruiting vegetables
Scythe pelargonic acid 0 12 no no no yes Non-selective control of small annual weeds and suppression of perennial weeds
Select Max clethodim 1 24 yes no no yes Grasses in many vegetable crops
Sharpen saflufenacil 14 12 yes yes yes yes Broadleaf weeds in corn (not fresh market sweet corn) and legume harvest aid
Shield EX tolpyralate 27 12 yes no no yes Some grass and broadleaf weeds in corn
Simazine 90 WDG simazine 5 12 no yes no no Many annual grass and some broadleaf weeds in corn
Sinbar WDG terbacil 5 12 yes yes no yes Some grass, yellow nutsedge (high rate), and broadleaf weeds in asparagus
Solicam DF norflurazon 12 12 yes no yes no Grasses, yellow nutsedge suppression, and many broadleaf weeds in asparagus
Sonalan HFP ethalfluralin 3 24 yes yes no no Many annual grasses and broadleaf weeds in beans and potatoes
Stinger clopyralid 4 12 yes no no yes Many broadleaf weeds in beets, corn, spinach, and turnips
Surpass EC acetochlor 15 12 yes yes yes no Some annual broadleaf and grass weeds in corn
Treflan HFP trifluralin 3 12 yes no yes no Many annual grasses and some broadleaf weeds in many vegetables
Valor EZ flumioxazin 14 12 yes yes no yes Grasses and many annual and perennial broadleaf weeds in sweet potato
Zidua pyroxasulfone 15 12 yes yes yes no Annual grass, yellow nutsedge suppression, and some broadleaf weeds in corn

1Trade Name - Example herbicide trade name for the active ingredient. There may be several formulations of the same active ingredient with different trade names. Inclusion in this guide is not an endorsement of the product.

2HRAC - Herbicide Resistance Action Committee resistance management numbers.

3Pre-SA - This herbicide can be applied to the soil before weeds have emerged.

4PPI - This herbicide can be applied before weeds have emerged and incorporated into the soil.

5Post - This herbicide can be applied after weeds have emerged.

Herbicides Alphabetically Listed by A.I. (Table 29)

Herbicides Alphabetically Listed by A.I. (Table 29) Evonne Gong
ACTIVE INGREDIENT EXAMPLE TRADE NAME ADDITIONAL TRADE NAME(S) SIGNAL WORD1 RESISTANCE GROUP (HRAC2 CODE) DERMAL LD503
(mg/kg)
ORAL LD504
(mg/kg)
RESPIRATOR REQUIRED?
2, 4-D 2,4-D Amine 4   D 4 >5050 1340 no
acetochlor Surpass EC Breakfree NXT, Cadence, Cadence NXT, Confidence, Fearless, GCS Acetochlor 7EC, Harness, Surpass NXT, TopNotch, Volley NXT W 15 >2240 (similar material) 1415
(similar material)
no
ametryn Evik DF   C 5 >2020 4494 yes
atrazine Aatrex 4L*   C 5 >5050 >5000 no
bensulide Prefar 4-E   C 0 >2000 960 no
bentazon Basagran 5L Bastante D 6 >2000 1260 no
bromoxynil Broclean Moxy 2E, Palouse C 24 >2 238 no
carfentrazone-ethyl Aim EC Antik EC, Longbow EC C 14 >4000 4077 no
clethodim Select Max Arrow 2 EC, Ceridian 2 EC, Cleanse 2EC, Clethodim 2E, Dakota, Intensity Post-Emergence Grass, Intensity One Post-Emergence Grass, Shadow, Shadow 3EC, Tide USA Clethodim 2EC, Trizenta 3EC, Trizenta, Volunteer, Willowood Clethodim 2EC C 1 >5000 >5000 no
clomazone Command 3ME Clomate 3ME C 13 >5000 >5000 no
clopyralid Stinger, Clean Slate GCS Clopy 360SL, Spur, Stigmata C 4 >5000 >5000 no
cycloate Ro-Neet   C 15 >5000 3129 yes
DCPA Dacthal Flowable EPA issued an emergency order on August 6, 2024 prohibiting all use, distribution, and sale of this product
dicamba Clarity BL1, Clash Selective, Dicamba 4, Rifle, Sterling Blue, Strut, Topeka, WC-DCB C 4 >2000 >2000 no
dichlobenil Casoron 4G   C 29 slightly irritating >5000 yes
dimethenamid Outlook   W 15 >5000 695 yes
diquat Reglone Aceto Diquat 2L AG, Capone Desiccant, Nufarm Diquat 2 L, Nufarm Diquat SPC 2 L, Verdure-X C 22 >5050 886 no
EPTC Eptam   W 15 2750 1325 yes
ethalfluralin Curbit, Sonalan HFP   D 3 >5 mL/kg 3267 no
fluazifop-p-butyl Fusilade DX Stockade  C 1 >2000 >5000 yes
flumioxazin Chateau EZ, Valor SX Chateau SW, Flumi 51 WDG, Flumi SC , Flumi SX, Flumioxazin 51% WDG, Maxunitech Flumi SC Ag, Outflank, Panther SC, Tuscany, Tuscany SC C 14 >5000 >5000 yes
fluthiacet-methyl Cadet   W 14 >2020 2537 no
fomesafen Reflex Forsyte 1.88 SL, Ringside, Top Gun Flex, Top Gun, Willowood Fomesafen 1.88 SL D 14 >2000 >982 no
glyphosate Roundup PowerMax 3 Abundit Edge, Buccaneer 5 Extra, Buccaneer Plus, Bullzeye HL-K, Cornerstone K, Cornerstone 5 Plus, Cornerstone Plus, Credit 41 Extra, Credit K6, Credit Xtreme, CropSmart Glyphosate 41% Extra, Duplicator 6, Duramax, Durango DMA, Four Power Plus, Gly Star Original, Gly Star Plus, Glyphogan, Glyphogan Plus, Glyphosate 4 Plus, Honcho K6, Imitator DA, Mad Dog, Mad Dog 5.4, Mad Dog K6, Mad Dog Plus, Makaze, Roundup PowerMAX, Roundup WeatherMAX, Shar-Max Glyphosate 41% SL, Tomahawk 4, Tomahawk 5, Willowood Glypho 5, Willowood Glypho 6 C 9 5000 5000 no
halosulfuron-methyl Sandea Halomax 75, Permit, Profine 75, Stadia C 2 >5000 1287 no
imazamox Raptor Beyond Xtra  C 2 >4000 >5000 no
linuron Lorox DF Linex 4L Agricultural  C 5 >2000 3489 no
mesotrione Callisto Argos, Atticus Cavallo 4 SC, BL4, Explorer, Mesotrione 4SC, MesoTryOne 4L, Motif , Seeker 4SC, Seeker, Sotrion, Willowood Mesotrione 4SC C 27 >5000 >5000 no
metribuzin Metribuzin Glory, Glory 4L, Glory FDF, Metricor 4F, Metricor DF, Me-Try-Buzin 4L, Me-Try-Buzin 75DF, Rancor 4 F, Rancor 75 DF, TriCor 4F, TriCor DF C 5 >2000 2365 no
napropamide Devrionol 2-XT Devrinol DF-XT C 0 >2000 >2000 no
nicosulfuron Accent Q Primero C 2 >5000 >5000 no
norflurazon Solicam DF   C 12 >2000 1140 no
oxyfluorfen Goal 2XL Collide, Galigan 2E, GoalTender, ScrollOVR, Scroll 2 XL, Willowood OxyFlo 2EC W 14 >5000 3129 no
paraquat Gramoxone SL 3.0* Axill Solutions Paraquat 3SL*, Gramoxone SL 2.0*, Helmquat 3SL*, Paraquat 43.2% SL*, Paraquat Concentrate*, Parazone 3SL*, Quik-Quat*, Willowood Paraquat 3SL* D (Poison) 22 1990 172.81 yes
pelargonic acid Scythe   W 0 >2000 >5000 no
pendimethalin Prowl H2O AquaPen 3.8, Framework 3.3 EC Hebicide, Pin-Dee 3.3 EC, Prowl 3.3 EC, Satellite Flex, Satellite HydroCap, Stealth C 3 >5000 >2000 no
prometryn Caparol 4L   C 5 >5000 >5000 yes
pronamide Kerb 50-W* Kerb SC C 3 >2000 (similar material) >5000 (similar material) no
pyroxasulfone Zidua Zidua SC C 15 >2000 >2000 yes
quinclorac Quinstar 4L   C 4 >5000 5000 no
quizalofop Assure II FirstAct, Targa D 1 >2000 (similar material) 5900 (similar material) no
rimsulfuron Matrix SG DuPont Matrix SG, Grapple, Hinge, Tetris SG, Tide Rimsulfuron 25WG C 2 >2000 >5000 no
saflufenacil Sharpen   C 14 >5000 >2000 no
sethoxydim Poast   W 1 >5000 5000 no
simazine Simazine 90 WDG, Princep 4L Simazine 4L, Simazine 4L Flowable, Simazine 90DF, Sim-Trol 4l Simazine Flowable, Sim-Trol 90DF Simazine Dry Flowable  C 5 >2000 >5000 yes
s-metolachlor Dual Magnum** Brawl II, Charger MAX, Cinch C 15 >2000 3425 no
sulfentrazone Aquesta 4F Maxunitech Sulfentrazone 4 SC, Passage, Shutdown, Spartan 4F, Sulfentrazone 4L, Sulfin 4SC, Zeus XC, Zone 4F C 14 >2000 300 - 2000 no
tembotrione Laudis   C 27 >5000 1750 no
terbacil Sinbar WDG   C 5 >5000 >5000 no
tolpyralate Shield EX   C 27 >2000 >2000 no
topramezone Impact Armezon  C 27 >2000 >2000 no
trifluralin TreflanHFP Treflan TR-10 Granular, Trifluralin 10G, Trifluralin 4EC, Trifluralin HF, Triflurex HFP, Trust C 3 >2000 >4013 no

1Signal Word - (C) Caution is least dangerous, (W) Warning is intermediate, (D) Danger is most dangerous

2HRAC - Herbicide Resistance Action Committee number

3Dermal LD50 - The lethal dermal dose of the herbicide for 50% of a test population, usually of rats

4Oral LD50 - The lethal oral dose of the herbicide for 50% of a test population, usually of rats

Crops Labeled for Each Herbicide Trade Name (Table 30)

Crops Labeled for Each Herbicide Trade Name (Table 30) Evonne Gong
TRADE NAME
ACTIVE INGREDIENT
Asparagus
Basil
Beans
Beet/Chard
Brassicas
Carrot Parsnip
Celery
Corn (Pop)
Corn (Sweet)
Cucurbits
Eggplant
Garlic
Globe Artichoke
Leek
Lettuce Endive
Okra
Onions
Parsley Cilantro
Peas, Green
Peppers
Potatoes
Pumpkins
Radish
Rhubarb
Rutabaga, Turnip
Spinach
Sweet Potato
Tomatoes
2,4-D Amine 4 2, 4-D R             R R                                      
Aatrex 4L* atrazine               R R                                      
Accent Q nicosulfuron               R R                                      
Aim EC carfentrazone-ethyl R R R R R R R R R R R R R R R R R R R R R R R R R R R R
Aquesta 4F sulfentrazone R   R   R         R R         R     R R       R R     R
Assure II quizalofop     R                               R                  
Basagran 5L bentazon     R         R R                   R                  
Broclean bromoxynil                       R         R                      
Cadet fluthiacet-methyl               R R                                      
Callisto mesotrione R             R R             R               R        
Caparol 4L prometryn           R R                 R   R           R        
Casoron 4G dichlobenil                                               R        
Chateau EZ flumioxazin R   R                 R R             R                
Clarity dicamba R                                                      
Clean Slate clopyralid R     R       R R                               R R    
Command 3ME clomazone R R R   R         R               R R R   R   R     R  
Curbit ethalfluralin                   R                       R            
Dacthal Flowable DCPA       EPA issued an emergency order on August 6, 2024 prohibiting all use, distribution, and sale of this product.
Devrionol 2-XT napropamide R R     R           R                 R             R R
Dual Magnum s-metolachlor R**   R R** R** R**   R R R**   R**         R**   R R** R R   R   R**   R
Eptam EPTC     R                                   R              
Evik DF ametryn               R                                        
Fusilade DX fluazifop-p-butyl R   R     R           R     R   R             R     R  
Goal 2XL oxyfluorfen         R             R R       R                      
Gramoxone SL 3.0* paraquat R   R   R R   R R R R R R   R R R   R R R R   R R   R R
Impact topramezone               R R                                      
Kerb 50-W* pronamide                             R                          
Laudis tembotrione               R R                                      
Lorox DF linuron R   R     R R                     R R   R     R        
Matrix SG rimsulfuron                                         R             R
Metribuzin metribuzin R         R                         R   R             R
Outlook dimethenamid     R R       R R     R   R     R       R   R   R   R  
Poast sethoxydim R   R R R R R R R R R R R R R R R R   R R R R R R R   R
Prefar 4-E bensulide         R   R     R R R     R   R R   R   R            
Princep 4L simazine               R R                                      
Prowl H2O pendimethalin R   R   R R R R R   R R R R     R   R R R             R
Raptor imazamox     R                               R                  
Reflex fomesafen     R                                   R              
Reglone diquat R                       R               R              
Ro-Neet cycloate           R                                       R    
Roundup PowerMax 3 glyphosate R R R R R R R R R R R R R R R R R R R R R R R R R R R R
Sandea halosulfuron-methyl R   R         R R R R   R     R       R   R   R       R
Scythe pelargonic acid R R R R R R R R R R R R R R R R R R R R R R R R R R R R
Select Max clethodim R R R R R R R     R R R   R R R R R R R R R R R R R R R
Sharpen saflufenacil     R         R R                   R                  
Simazine 90 WDG simazine               R R                                      
Sinbar WDG terbacil R                                                      
Solicam DF norflurazon R                                                      
Sonalan HFP ethalfluralin     R                                   R              
Stinger clopyralid       R R     R R                               R R    
Surpass EC acetochlor               R R                                      
TreflanHFP trifluralin R   R   R R R     R R         R R   R R R   R   R     R
Valor EZ flumioxazin                                                     R  
Zidua pyroxasulfone               R R                                      

*Federally restricted herbicide

**Indicates an indemnified label for use in this crop due to potential for crop injury. Users must agree to a waiver of liability through the Syngenta website to access the label for this use.

Select Weeds Controlled by Herbicide Active Ingredients According to Labels (Table 31)

Select Weeds Controlled by Herbicide Active Ingredients According to Labels (Table 31) Evonne Gong
Table 31: Select Weeds Controlled by Herbicide Trade Names According to Labels
TRADE NAME ACTIVE INGREDIENT Annual Bluegrass Barnyard Grass Crabgrass Fall Panicum Foxtail Goosegrass Johnsongrass (rhizome) Johnsongrass (seedling) Quackgrass Yellow Nutsedge Bindweed Carpetweed Chickweed Cocklebur Galinsoga Jimsonweed Lambsquarters Morning Glory Mustard Nightshade Pigweed Purslane Ragweed Smartweed Velvetleaf Wild Buckwheat
2,4-D Amine 4 2, 4-D                     H C C C C C C C C   H C C C H  
Aatrex 4L* atrazine C PC PC   PC                 C   C C C C C C C C C PC C
Accent Q nicosulfuron   C         C C C             C   C     C     C    
Aim EC carfentrazone-ethyl                     H H       H C C   C C     C C  
Aquesta 4F sulfentrazone     C     C       C   C C   C C C C C C C C   C    
Assure II quizalofop   C C C C C C C C                                  
Basagran 5L bentazon                   H H     C H C C H C H   H H C C  
Broclean bromoxynil                                 C PC PC C PC   PC C PC C
Cadet fluthiacet-methyl                               C C C   C C     C   PC
Callisto mesotrione     C             PC   C C C C C C PC C C C   PC C C PC
Caparol 4L prometryn   C C C C C               C     C C C C C C C C    
Casoron 4G dichlobenil C   C   C       C C   C C       C   C   C C C C    
Chateau EZ flumioxazin C C C C C C   C     PC C C     C C C C C C C C C C C
Clarity dicamba                     C C C C   C C C C C C C C C C C
Clean Slate clopyralid                               C       C     C PC   C
Command 3ME clomazone   H H C C C   H             H H H         H   H C  
Curbit ethalfluralin     C C C C   C       C         C       C C        
Dacthal Flowable DCPA EPA issued an emergency order on August 6, 2024 prohibiting all use, distribution, and sale of this product.
Devrionol 2-XT napropamide C C C C C C   C       C         C       C C C      
Dual Magnum** s-metolachlor   C C C C C   PC   C         C         PC C PC        
Eptam EPTC C C C C C C   C C C   C C       C C   C C C        
Evik DF ametryn   C C C P C               C     C C C   C   C C C  
Fusilade DX fluazifop-p-butyl   C C C C C H C H                                  
Goal 2XL oxyfluorfen                               C C C C C C C   C C  
Gramoxone SL 3.0* paraquat C C C C C C   PC PC   PC C C C C C C PC C C C C PC C C C
Impact topramezone   H H H C C   H     PC C C C C C C PC C C C PC C C C  
Kerb 50-W* pronamide C C C C C C           C C       C C C C   C   C    
Laudis tembotrione   C C   C C           C C C C C C PC C C C   C C C PC
Lorox DF linuron   C C C C C           C C PC C   C PC C PC C C PC   PC  
Matrix SG rimsulfuron   C C C C C           C C C     C C C   C C C C C C
Metribuzin metribuzin C C C C C     PC PC PC     C PC     PC PC C PC C C PC PC PC  
Outlook dimethenamid   C PC C PC C   C       C   PC C C C   C   C C C C C  
Poast sethoxydim C C C C C C   C   C   C         C     C C C C      
Prefar 4-E bensulide   C C C C C C C C                                  
Princep 4L simazine C C C C C C           C C       C C C C C C C C    
Prowl H2O pendimethalin   C C C C C                                        
Raptor imazamox   C C C C C   C         H       C   C C C C   C H  
Reflex fomesafen   PC PC   C       PC PC     C C   C C PC C C C PC   PC C PC
Reglone diquat   PC PC PC PC PC   PC     PC C   C   C C C C C C C C C C  
Ro-Neet cycloate C C C   C         C             C     C   C     C  
Roundup PowerMax 3 glyphosate C C C   C         C             C     C C C        
Sandea halosulfuron-methyl C C C C C C C C C C C C C C C C C C C C C C C C C C
Scythe pelargonic acid                   C     C C C C C PC C   C C C C C  
Select Max clethodim C C C C C C H C C                                  
Sharpen saflufenacil                     PC C PC C C C C C C C C C C C C C
Simazine 90 WDG simazine C C C C C C           C C       C     C C C C C    
Sinbar WDG terbacil C C C C C       H H     C       C   C C   C   C    
Solicam DF norflurazon C C C C C C PC C PC PC   C C PC     PC PC C PC PC C PC PC C  
Sonalan HFP ethalfluralin C C C C C     C       C C       C     H C C       C
Stinger clopyralid                           C C C       C     C PC   C
Surpass EC acetochlor   C C C C C   PC       C     C   C     C C C   C    
TreflanHFP trifluralin C C C C C     C     C C C       C       C C        
Valor EZ flumioxazin C C C C C C   C     C C   C   C C C C   C C C C C  
Zidua pyroxasulfone C C C C C C   C   PC   C PC     PC PC PC   C C C PC   PC PC

C = Control

H = Control at high rate

PC = Partial control/suppression

* Federally restricted herbicide