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Glufosinate is a non-selective, contact herbicide that controls annual and perennial grasses and broadleaf weeds. It is a foliar-applied product typically used in post-emergence applications on Enlist®, XtendFlex®, LibertyLink® soybeans and other glufosinate-tolerant crops, including canola, cotton and corn.
Glufosinate can also be used for broadcast burndown of weeds before planting or prior to crop emergence in any conventional variety of canola, sweet corn, corn, cotton, soybean or sugar beet.
Because glufosinate must contact growing leaf tissue to control weeds, it has no activity on non-emerged weeds. A strong pre-emergence herbicide program that contains multiple modes of action, combined with a timely layered post-emergence residual, can provide a solid foundation for weed management programs that include glufosinate.
The active ingredient in glufosinate herbicides is glufosinate ammonium, first derived from the soil bacteria Streptomyces viridochromogenesa.
Glufosinate is a Group 10 nitrogen metabolism inhibitor herbicide. It controls weeds by inhibiting the glutamine synthetase enzyme, which plays a critical role in nitrogen metabolism.
Glufosinate is a contact herbicide, meaning the active ingredient is only effective when it comes into contact with plant tissue. Uniform spray coverage is required to achieve adequate weed control.
With uniform, thorough spray coverage and good growing conditions, necrosis of leaves and young shoots occurs within 2 to 4 days after glufosinate application.
Weed control may be reduced if application is made when heavy dew, fog, and mist/rain are present or when weeds are under stress due to environmental conditions such as drought, cool temperatures or extended periods of cloudiness.
Glufosinate requires contact with healthy plant tissue to control weeds effectively. Leaf wetness soon after glufosinate application can wash the product off foliage, leading to the potential need for reapplication. Glufosinate is generally rainfast four hours after application for most weed species, so it&#;s important to consider future weather forecasts when making spray applications.
Applications should be made between dawn and two hours before sunset to avoid the possibility of reduced lambsquarters and velvetleaf control. Spraying between 10 a.m. and 2 p.m. on hot, sunny, humid days will maximize glufosinate performance.
Microorganisms quickly degrade glufosinate in the soil; therefore, it has little to no soil residual activity to control non-emerged weeds.
For broad-spectrum, long-lasting weed control, glufosinate may be tank-mixed with postemergence residual herbicides, including Group 14 or Group 15 products like fomesafen, lactofen or s-metolachlor for labeled crops. Remember to consult the product label for specific tank-mixing best practices.
Glufosinate can be applied post-emergence broadcast on glufosinate-tolerant canola, corn, cotton and soybeans. After carefully reviewing the label on the product you plan to use, you can apply glufosinate throughout the growing season in conjunction with crop height restrictions.
To avoid severe crop injury, do not apply glufosinate post-emergence to non-tolerant crops.
Glufosinate herbicides can also be applied as a standalone burndown herbicide in the fall and spring, but it is better to tank mix with different herbicide modes of action to reduce the risk of glufosinate herbicide weed resistance.
Glufosinate application rates will vary depending on the product, crop, targeted weed species and environmental conditions.
For example, for Willowood Glufosinate 280SL, labeled post-emergence application rates are 22 or 29 fluid ounces per acre for most crops, depending on weed height or diameter. A minimum of 10 gallons of water per acre carrier volume and 80-degree or 110-degree flat fan nozzles are strongly advised for optimum spray coverage and canopy penetration.
Under dense weed/crop canopies, a broadcast rate of 15-20 gallons of water per acre should be used to obtain thorough spray coverage. Consult the product label for specific application rate guidance.
Adding ammonium sulfate to the tank mix may increase glufosinate performance, particularly under low humidity conditions or when using high-pH water. Glufosinate requires more AMS per gallon than glyphosate (up to 3 lbs/acre), so consult the product label for optimal rates.
Anti-foam or drift control agents may also be added to glufosinate tank mixes if needed. Adding surfactants or crop oils may increase the risk of crop injury, so consult the herbicide label to confirm best practices for your situation.
Glufosinate use has increased in recent years partly due to its compatibility with Enlist soybean weed management programs. Overuse may lead to herbicide resistance issues, so it&#;s important to use an integrated weed management plan to manage risk. Here are a few tips to consider as you develop a weed control strategy that includes glufosinate:
Make timely herbicide applications when weeds are 4&#; or smaller
Use multiple modes of action
Use layered residuals to extend the window of weed control
Add effective adjuvants to improve spray performance and plant uptake
Scout fields after applications to verify the application was effective
Add cultural or mechanical weed control practices, including tillage
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Applicators should use best safety practices when using glufosinate. These include:
Respecting the glufosinate restricted entry interval (REI) of 12 hours (field scouting and irrigation pipe moving may require longer REI times)
Wearing appropriate personal protective equipment, including a long shirt, pants, eyewear, chemical-resistant gloves and close-toed shoes when handling glufosinate
Washing hands after handling the herbicide
Removing clothing and PPE immediately after handling glufosinate
Following all label instructions to ensure the safe use of glufosinate
Keep the glufosinate containers tightly closed and dry in a cool, well ventilated place, and protect against sunlight. Storage temperature must not exceed 125°F. Glufosinate waste may be disposed of on site or at an approved waste disposal facility.
Glyphosate and glufosinate are two of the most widely used herbicides in agriculture. Glyphosate can be applied post-emergence to glyphosate-resistant (Roundup Ready®) crops, while glufosinate is safe for post-emergence applications in glufosinate-resistant (LibertyLink
*No endorsement is implied in the referencing of trade names.
Glufosinate is a nonselective foliar herbicide used for broadcast burndown application before planting or prior to emergence of canola, corn, sweet corn, soybean, and sugar beet. It can also be applied post-emergence to glufosinate-tolerant canola, corn, sweet corn, and soybean; however, spray contact with non-tolerant crops can result in injury. Other labeled uses of glufosinate include directed postemergence applications around trees, vines, and berries, as well as potato vine desiccation. In addition to agricultural uses, some glufosinate products can be used to control plants along landscape borders and around ornamental trees.
Glufosinate provides control of many annual broadleaf and grass weeds; however, control of large or well-tillered annual grasses, such as yellow foxtail, wild oat, or volunteer cereals, can be marginal. Glufosinate also provides suppression of some perennial weeds. Glufosinate has no soil activity.
Approximately 800,000 pounds of glufosinate were sold in Minnesota in .1 A USDA:NASS Survey, indicated that glufosinate was applied to 1% of corn acres, and 2% of soybean acres in the state.2 It was applied on up to 11% of the acres in specific counties (Wilkins). As glyphosate resistant weeds become more prevalent, glufosinate use may increase as an alternative herbicide option.3
Glufosinate controls weeds by inhibiting glutamine synthetase (herbicide site of action 10), an enzyme involved in the incorporation of ammonium into the amino acid glutamine. Inhibition of this enzyme causes a buildup of phytotoxic ammonia in plants which disrupts cell membranes. Glufosinate is a contact herbicide with limited translocation within the plant. Control is best when weeds are actively growing and not under stress.
Due to its contact activity, thorough spray coverage is needed for effective weed control. This is achieved by:
Glufosinate tolerant cultivars of corn, sweet corn, soybeans, and canola are available for use in Minnesota and marketed under the LibertyLink® name. In addition, Enlist E3 soybean varieties are available which are tolerant to glufosinate as well as glyphosate and 2,4-D. Only 2,4-D choline products, Enlist One® and Enlist Duo®, can be applied on LibertyLink® crops. Check the pesticide labels carefully prior to application.
Herbicide resistance is the inherited ability of a plant, such as weeds, to survive an herbicide application that the original population was susceptible to. The development of resistance to herbicides is a growing concern for weed management because it can lead to the loss of herbicide options, which can have important economic and environmental consequences.3
Glufosinate resistant Italian ryegrass, Lolium perenne ssp. Multiflorum, has been reported in Oregon and California.4 Resistance in other weed species such as perennial ryegrass (Lolium perenne), ridged ryegrass (Lolium rigidum), and goosegrass (Eleusine indica) have been found in other parts of the world. Glufosinate resistant weed species have not been reported in Minnesota. To prevent the development of resistant weeds, utilize practices such as combing and rotating herbicides sites-of-action and mechanical weed control.3
Glufosinate movement in soil depends on both soil properties and pesticides properties. The leaching potential of glufosinate is reduced with increasing soil clay and organic matter content. According to the National Pesticide Information Center&#;s Herbicide Properties Tool, glufosinate is likely to reach shallow groundwater in sandy soils (Koc = 10) but not in silty loam soils (Koc = 250).5 However, in soil column experiments, glufosinate and its degradants did not leach further than 6 inches in loam or clay soils, or further than 24 inches in sandy soils.6
Movement of glufosinate to surface water can occur dissolved in runoff water or adsorbed to eroding soil. Runoff loss is greatest if a surface water runoff event occurs shortly after application. Glufosinate may also move offsite via drift during application.
The MDA started monitoring for this pesticide in . Water Quality Portal7 data indicated that glufosinate was detected in 0.7% of groundwater samples and 1.1% of surface water samples in the United States. The highest concentrations detected in groundwater and surface water on the Water Quality Portal were 4.5 and 3.2 ug/L, respectively. The Minnesota Department of Health has established a drinking water reference value for glufosinate of 5 µg/L. The lowest Environmental Protection Agency (EPA) OPP (Office of Pesticide Products) aquatic life benchmark for glufosinate is 72 ug/L for non-vascular plants.
Glufosinate is very toxic to non-target plants. Since it is a contact herbicide, drift of a small volume of spray can result in necrotic vegetation. However, thorough spray coverage would be needed to kill plants, especially if larger in size.
Glufosinate is moderately toxic to fish and aquatic invertebrates with a lethal concentration, LC50, of > ug/L for both rainbow trout and water flea.7 Glufosinate is slightly toxic to mammals and birds through ingestion with acute oral LD50 values > mg/kg. Glufosinate is classified as practically non-toxic to adult honeybees on an acute contact and oral exposure basis, LD50 >100 μg ai/bee. However, the EPA states in their interim decision for glufosinate that "the Agency is unable to assess risks to pollinators at the present time" and may require additional pollinator studies related to honey bee chronic and larval toxicity testing before a final registration review decision is made for glufosinate. The toxicity of glufosinate degradates is similar to or lower than the parent compound.
Evaluation of human dietary exposure to glufosinate and its breakdown products by the EPA showed that the greatest risk from glufosinate was from contamination of drinking water. However, observed levels of exposure were found to be below levels of concern and were not considered a reasonable adverse health risk. Based on rodent studies, glufosinate is classified as not likely to be carcinogenic in humans.8
Glufosinate is a slight skin irritant and a severe eye irritant.9 EPA evaluation determined that short and intermediate term dermal exposure was not a concern if label personal protective equipment requirements, such as goggles and gloves, are utilized. The restricted entry interval for glufosinate treated areas varies among products, crops, and type of field activity.
1Minnesota Department of Agriculture. . Pesticide Sales Database. Accessed March 25, .
2Minnesota Department of Agriculture, USDA: NASS Minnesota Field Office, . Pesticide Usage on Four Major Crops in Minnesota.
3Ohio State University Extension. Weed Control Guide for Ohio, Indiana and Illinois. Bulletin 789.
4 Heap, I. The International Herbicide-Resistant Weed Database. www.weedscience.org. Accessed March 30, .
5National Pesticide Information Center. Herbicide Properties Tool. http://npic.orst.edu/HPT/. Accessed March 30, .
6United States Environmental Protections Agency. Fate and Ecological Risk Assessment for the Registration Review of Glufosinate.
7National Water Quality Monitoring Council. Water Quality Portal. Accessed March 25, .
8Donovan, W.H., D. Dotson, and K. Rury. June 19, . USEPA Memorandum: Glufosinate ammonium. Updated of revised acute and chronic aggregate dietary assessment (food and drinking water) exposure assessment in support of the petition proposing tolerances for residues of glufosinate ammonium in citrus fruits, pome fruits, stone fruits, olives, and sweet corn. CAS No: -82-2. Decision No. . https://deq.mt.gov/Portals/112/Water/WQPB/Standards/Glufosinate.pdf?ver=-12-23--317
9United States Environmental Protection Agency. Reregistration Review of Glufosinate Ammonium (PC Code ). Docket ID: EPA-HQ-OPP--. . Accessed 4/12/20.
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