What is glyphosate?

Glyphosate is a weed killer used on farms, along roads and in gardens. This page covers what it is, how it works on plants, and when farmers use it. It does not make claims about health. For what regulators have concluded, see Where agencies stand.

The basics

• It is an herbicide. It is sprayed on the leaves of plants and kills both broadleaf plants and grasses.¹
• It is non-selective. It will kill most plants it lands on, unless a crop has been bred to tolerate it.¹
• It works on a plant enzyme. Glyphosate blocks an enzyme pathway called the shikimic acid pathway. Plants and some microorganisms need this pathway to make certain proteins.¹ The U.S. Environmental Protection Agency (EPA) describes it as targeting "a growth enzyme in plants."²
• It has been on the U.S. market since 1974. That is the year it was first registered with EPA.²¹
• It comes in several forms. These include an acid and several salts.¹
• It is widely used. The European Commission calls it "one of the most used and the most extensively studied pesticides in the world."³

Where it is used

EPA lists glyphosate uses on a long range of crops, including corn, soybean, canola, cotton, sugar beet, alfalfa, cereal grains and legume vegetables. It is also used on pastures, forests, rights-of-way, parks, lawns and other non-crop sites.²

EPA says broad weed control from glyphosate lets growers use reduced-tillage and no-till systems.²

When it is applied on farms

Farm uses fall into three broad timings. Our spray calendar shows typical months by crop and region, with a source for each row.

1. Burndown, before planting or after harvest. Glyphosate clears weeds or cover crops that have already come up. Purdue Extension describes spring burndown "almost any time before planting," allowing 7 to 10 days for glyphosate to work.⁴ The European Commission says glyphosate products are "typically applied before crops are sown."³
2. In-crop, on tolerant varieties. Some corn, soybean and canola varieties are bred to tolerate glyphosate. Manitoba Agriculture's 2026 crop protection guide lists in-crop glyphosate for these crops "for use on glyphosate tolerant varieties only."⁵
3. Pre-harvest, shortly before harvest. In Canada, glyphosate was first registered in 1992 for pre-harvest use on wheat, barley, soybeans, peas, lentils, canola and flax. The label said to apply at 30% grain moisture or less, typically 7 to 14 days before harvest.⁶ Canada's Keep it Clean program says glyphosate is registered there for pre-harvest weed control only and "is not registered for use as a desiccant."⁷ In the European Union, pre-harvest uses "for desiccation to control the time point of harvest or to optimise threshing are not permitted."³

Limits on food

• United States. EPA sets a tolerance, which is the legal limit on how much residue may remain on a food or feed crop. Glyphosate tolerances are listed in 40 CFR § 180.364.²
• Canada. Health Canada sets Maximum Residue Limits (MRLs) for glyphosate. For example, the Canadian Food Inspection Agency's 2015-2016 survey compared samples to MRLs of 5 ppm for wheat, 10 ppm for barley and 4 ppm for lentils.⁸

Glyphosate and USDA Certified Organic

The rules for USDA Certified Organic do not allow glyphosate. The USDA Agricultural Marketing Service says herbicides containing glyphosate are prohibited in organic crop production.⁹ USDA Certified Organic is a rule about how food is grown. It is not a residue test. See Certifications explained.

Sources