|Trade Names: Roundup (many forms), Glyfos, Glystar, many others||Common Name: glyphosate||Formulations: 4L*, 5.5L, 90 WD, many others|
Nonselective, foliar-applied, systemic, postemergence control of most weeds – broadleaves, grasses, sedges and many woody species. Uses include:
- Site preparation – general weed control before planting most crops or landscape plants.
- Postemergence directed or spot spray for general weed control in established woody crops, including Christmas trees, nurseries and landscape plantings.
- Broad spectrum weed control in glyphosate-resistant (Roundup-Ready®) crops
- Weed control under benches and in walkways of greenhouses when no plants are in the house.
- General weed control in non-crop areas including residential and commercial lawns, golf courses, sod farms, etc.
- Certain formulations are labeled for use in aquatic sites and irrigation canals for non-selective weed control.
- May be used in cut-stem application for woody weeds, or applied with a wick or wiper to weeds that are taller than the crop.
|Amount of Active Ingredient||Amount by Formulation|
|Per Acre||1 to 5 lb||1 to 5 qt||0.9 to 4.4 lb|
|Per 1,000 sq. ft.||0.3 to 1.8 oz||0.3 to 1.6 oz||0.22 oz to 1.6 oz|
|Spot Treatment||1.3 to 2.67 oz/gal spray||see label|
Major Weeds Controlled
Glyphosate is a nonselective herbicide. Most plants are controlled or severely injured. Established weeds require a higher dose or repeated application than small seedling weeds.
Major Weeds Not Controlled
Several species are not well controlled by glyphosate including dayflower, doveweed, cutleaf eveningprimrose, established white clover, morningglory and several pine species. Weeds under poor growing conditions such as water stress or disease and insect damage may show erratic or reduced control. Many perennial weeds, particularly woody species, are not well controlled when treated at non-optimal times. Field horsetail (Equisetum arvensis) is not well controlled.
RESISTANT WEEDS: Several weed species have developed resistance to glyphosate including horseweed, palmer amaranth, ragweed, and annual ryegrass.
For Best Results
Apply to actively growing plants. Do not apply if rainfall or overhead irrigation will occur within 1.5 to 6 hours, depending upon the formulation used. Check label for specific guidelines. Treat before mowing or after regrowth to specified size as described on the label. Coverage should be uniform and complete, but do not apply to the point of runoff. Season of application is very important for controlling many perennial weed species. Generally, deciduous perennial weeds or herbaceous perennials are best controlled by late summer / early fall applications before plants senesce. Evergreen perennials, like English ivy, are often better controlled by spring applications. The addition of an adjuvant may be necessary for some formulations; consult label for details. May be applied using a wiper, or as a cut-stem / cut-stump treatment; see product labels for specific guidance on these uses.
Cautions and Precautions
Avoid contact with foliage, green stems, or fruit of desirable plants since severe injury or death may result. Injury to plants receiving small amounts of drift may be expressed one to two years after the occurrence. Do not use more than 25 gallons of spray solution per acre. Keep people and pets off treated areas until dry to prevent transfer to desirable foliage. Limited amounts of drift to leaves will damage many plants.
Residual Activity (In Soil)
While glyphosate may be moderately persistent in soil, it is rapidly bound by clay particles and is not bioavailable resulting in no soil residual activity; however, in soilless substrates or pure sands, crop injury from root uptake has been observed.
Volatility and Leaching Potential
The vapor pressure is very low rendering it nonvolatile. Off-target drift may cause injury to non-target plants. Although glyphosate is very water soluble, it binds rapidly and tightly to soil colloids so that leaching does not occur. Further, glyphosate has a low tendency to runoff unless it is sorbed to eroding soil colloids.
Fate in Water
Glyphosate is highly soluble in water. Further, hydrolytic or photolytic processes do not readily degrade glyphosate and major reductions in water are due to sediment adsorption and microbial degradation.
Symptoms, Mode of Action, and Degradation
Absorbed through foliage and green stems and translocated throughout the plant. Growth inhibition occurs within days, but symptoms may take 7 to 10 days to develop. Symptoms include general chlorosis followed by senescence. Woody plants that are not killed may show injury symptoms on the new growth for two or more years. The symptoms may include chlorotic, strap-shaped leaves, shortened internodes, and witches-brooming. Mechanism of action involves inhibition of aromatic amino acid synthesis (a process unique to the plant kingdom) and the primary route of degradation is microbial. Additional information on glyphosate injury symptoms is available in the herbicide injury factsheet Glyphosate.
|Worker Protection Standards||REI: 4 hours|
|PPE: coveralls, waterproof gloves, shoes plus socks|
|Manufacturer: Bayer, many others||EPA Reg. # 524-475|
* Caution: When the product is available in more than one formulation, the formulation designated with the asterisk (*) was used as the primary source of information for this publication.
Updated Toxicology Information – The Debate Continues
Update: April 2023
Little has changed since the 2022 update. The USEPA has withdrawn its interim decision on glyphosate based upon a court finding that EPA had not adequately addressed questions about impacts on Endangered Species (required by the Endangered Species Act). The EPA has maintained the labels and registrations of glyphosate but is continuing its on-going review. For more information: here is the EPA document outlining the withdrawal as well as the processes included in the review https://www.regulations.gov/document/EPA-HQ-OPP-2009-0361-14447. According to this EPA document the final review is not expected until 2026! In my opinion.. a very dissapointing long time frame for completing this review.
Update January 2022
Much has happened since the last update in 2019, and yet little has changed. Three law suits have concluded with rulings that glyphosate did contribute to the plaintiff's cancer; two law suits concluded glyphosate had not contributed to the plaintiff's cancer. Rulings are being appealed. And It appears that the issue may ultimately have to be decided at the U.S. Supreme Court. Glyphosate remains labeled and available. But many weed control professionals are choosing to use alternatives. Here is a fact sheet that describes and discusses alternatives to glyphosate for weed control in landscapes.
Update: May 1, 2019:
On April 30th, EPA announced the availability of the proposed registration review decision for glyphosate. From the report:
" Today, the U.S. Environmental Protection Agency (EPA) is taking an important step in the agency’s review of glyphosate. As part of this action, EPA continues to find that there are no risks to public health when glyphosate is used in accordance with its current label and that glyphosate is not a carcinogen. The agency’s scientific findings on human health risk are consistent with the conclusions of science reviews by many other countries and other federal agencies."
January 2019 Update:
Recently, concerns have been expressed about the safety of glyphosate. This has also been the subject of litigation. Although hazard analysis by some non-governmental organizations have raised concerns, In 2016 the US EPA released a report from a review of glyphosate carcinogenicity and concluded that glyphosate is "not likely to be carcinogenic to humans." This conclusion is consistent with conclusions of other regulatory agencies. The full EPA report is available.
More recently (2017) EPA released a draft review of glyphosate human health and ecological risk assessments.
This draft human health risk assessment concludes that glyphosate is not likely to be carcinogenic to humans. The Agency’s assessment found no other meaningful risks to human health when the product is used according to the pesticide label. The Agency’s scientific findings are consistent with the conclusions of science reviews by a number of other countries as well as the 2017 National Institute of Health Agricultural Health Survey. EPA’s human health review evaluated dietary, residential/non-occupational, aggregate, and occupational exposures. Additionally, the Agency performed an in-depth review of the glyphosate cancer database, including data from epidemiological, animal carcinogenicity, and genotoxicity studies. The ecological risk assessment indicates that there is potential for effects on birds, mammals, and terrestrial and aquatic plants.
And, in January 2019, Health Canada released a re-review of glyphosate. This statement from the review sums up the conclusions: "No pesticide regulatory authority in the world currently considers glyphosate to be a cancer risk to humans at the levels at which humans are currently exposed. "
The International Agency for Research on Cancer (IARC) classification of gyphosate as a "probable human carcinogen" in 2015 continues to fuel this controversy. The IARC classification is based on a "hazard analysis". This analysis considers whether or not the substance could cause cancer if you have sufficient exposure. In contrast, regulatory agencies (like the US EPA) conduct a “risk analysis” which does consider the likelihood (or probability) of exposure to the chemical at doses high enough to cause an effect. Here is a link to a video that describes the difference between hazard and risk assessment.
Does this mean glyphosate is "safe"? It is my opinion that we must limit our exposure to all pesticides, including glyphosate. When using any pesticide: wear appropriate protective clothing, use it carefully to avoid off-target deposition, store the pesticide in a safe and secure site, and follow all label directions. A detailed summary of glyphosate properties, environmental fate and toxicology can be found in the National Pesticide Information Center fact sheet on glyphosate.
Publication date: Feb. 29, 2016
Revised: April 27, 2023
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