Best Practices to Manage Glyphosate Resistance

Glyphosate resistance in weeds continues to impact farmers across the United States, causing a shift in weed management. This trend is similar to previously developed weed resistance to ALS inhibitors, triazines and PPO inhibitors. HPPD inhibitors have also been added to the list of herbicides with documented resistance.

Compounding the problem are aggressively resistant weed species, such as waterhemp, Palmer amaranth (Palmer pigweed), marestail and others, which can make some fields a lost cause for growing corn, soybeans and cotton. Consider these research findings:

Mature waterhemp in an Illinois field
Mature waterhemp in an Illinois field. Photo courtesy of Aaron G. Hager, University of Illinois.
  • Corn: High-weed-density research during the 2014 weed competition variety trials at South Dakota State University (SDSU) recorded a 20- to 40-bushel-per-acre yield loss even when glyphosate was first applied two to three weeks after corn and weed emergence. Corn is sensitive to early-season weed competition, and SDSU recommends using pre-emergence residual herbicides in corn. Pre-emergence residual herbicides are also recommended in soybeans to prevent yield loss and minimize selection of glyphosate-resistant weeds.

  • Soybeans: Glyphosate resistant weeds are even more prevalent on soybeans acres, according to a USDA Economic Research Service study. This research looked at a cropping scenario which estimated that growers in a continuous soybean system can realize an extra $22.60 per acre return by managing resistance vs. ignoring resistance. Growers using a corn-soybean rotation can realize a $55.80 per acre advantage by managing glyphosate weed resistance. Additionally, in a Michigan State University study, Palmer amaranth seeds collected from a St. Joseph County, Mich., soybean field were confirmed resistant to glyphosate, and some of those resistant Palmer amaranth plants survived a 32X rate of glyphosate. The serious threat of economic losses from glyphosate-resistant weeds demands soybean farmers' attention to use alternatives.

  • Cotton: Left uncontrolled, glyphosate-resistant Palmer amaranth can result in a single plant producing as many as 1,000,000 seeds deposited into the soil seedbank. Recent research published by the Weed Science Society of America (WSSA), shows that glyphosate-resistant weeds such as Palmer amaranth can completely devastate cotton yields. Three years after researchers released 20,000 Palmer amaranth seeds into four different cotton fields, resistant weeds infested up to 100 percent of the fields. Farmers should be aware of how quickly resistant weeds can spread and make fields a total crop loss.

Experts agree that the only acceptable goal for managing resistant weeds is to have zero tolerance for the distribution of seeds by resistant weeds. The old way of thinking of weed control as an economic threshold is obsolete.

Read more on zero tolerance, alternatives to glyphosate and best management practices.

Crop Science Solutions

Crop Science has a broad portfolio to combat tough-to-control and resistant weeds. A well-thought-out herbicide program, using multiple modes of action, should be implemented to sustainably manage weeds. Before applying any herbicide, please read the entire label for the best possible results and to confirm that the product is effective on the weeds you wish to control. Not every product is suitable for every situation, and use of the correct application technique will ensure the best results.

The following Crop Science solutions are valuable tools to consider for your program.


When managing corn crops for high yields, remember it’s always best to start with a clean field. Start with an Autumn™ Super (2) application in the fall, and the following spring use Corvus® (2, 27), a pre-emergence residual herbicide which has overlapping modes of action to control early season problem weeds. Corvus pre-emergence herbicide from Crop Science is the only corn herbicide to offer burndown, residual and reactivation. Residual activity prevents new weeds, while reactivation controls late weeds.

The multiple modes of action in Corvus deliver consistent, broad-spectrum control of grasses and broadleaf weeds, including weeds resistant to glyphosate-, ALS-, PPO- and triazine-based herbicides.

A wide application window allows for application from pre-plant to early postemergence at V2, making it an effective, long-lasting first pass herbicide in a two-pass system. Depending on the weed spectrum in your field, such as fields without heavy Palmer amaranth and waterhemp pressure, Corvus may still be a great one-pass option.

A recommended two-pass program starts with a pre-emergence application of Corvus herbicide. The second pass should include a postemergence product such as Laudis® herbicide (27). If using Laudis following an application of Corvus, add another effective herbicide with a different mode of action, such as DiFlexx™ (4) herbicide, Liberty® (10) or atrazine, to ensure you are using multiple modes of action in your weed control.

Another pre-emergent herbicide Crop Science offers corn growers is Balance® Flexx (27). Follow a pre-emergent application of Balance Flexx with a postemergence herbicide to control multiple weed flushes. Balance Flexx has the unique power to reactivate with as little as a half-inch of rain to control late-emerging weeds. It controls glyphosate-, triazine-, PPO- and ALS-resistant weeds, including resistant marestail, common ragweed, waterhemp and Palmer amaranth. Balance Flexx even controls tough grasses, such as woolly cupgrass.

Balance Flexx fits into many cropping systems. Its superb weed control power combined with state-of-the-art crop safety innovation enables growers to readily rotate from corn to other key crops with little or no delay. 

Capreno® herbicide (2, 27) is a postemergence herbicide option for corn from Bayer. It has the longest-lasting residual of any post product on the market. With multiple modes of action, Capreno controls more than 65 grasses and broadleaves, including those resistant to glyphosate, PPO, ALS, dicamba and triazines.

Liberty® is the preeminent weed management system with a unique chemistry and novel mode of action to offer superior control of a broad spectrum of resistant and tough-to-control weeds in LibertyLink® corn. It is THE non-selective post-emergence herbicide that still effectively handles grasses and broadleaf weeds including glyphosate resistant Palmer amaranthgiant ragweed, marestail, waterhemp and kochia.

Learn more about products Bayer offers to help control weeds in corn as part of an integrated weed management program.


Crop Science offers soybean grower season-long weed control options starting with the decision to purchase LibertyLink® soybeans.  LibertyLink soybeans are widely available in many soybean brands including Credenz®. This year’s soybean herbicide program allows grower to start and finish clean with the inclusion of a full line up of residual products from FMC combined with the powerful control of Liberty® (10) herbicide and finishing with Autumn™ Super (2) in the fall after harvest.            

Liberty herbicide is the only group 10 herbicide that offers superior control of a broad spectrum of resistant weeds and tough-to-control weeds including palmer amaranth, waterhemp, marestail, giant ragweed, and kochia. To learn more about how to S.T.O.P. weeds with Liberty, visit for proper application tips.

As Bayer continues to anticipate the needs of farmers in the future, we continue to invest in developing leading edge technologies like Balance™ GT soybeans and Balance® Bean herbicide*.

Learn more about products Bayer offers to help control weeds in soybeans as part of an integrated weed management program.

*Balance Bean is not yet registered for sale or use in the United States. Balance GT is deregulated in the United States and authorized in some key importing countries. Additional international authorizations are pending.


Crop Science offers cotton growers Liberty® (10), the preeminent weed management system with a unique chemistry and novel mode of action to offer superior control of a broad spectrum of resistant and tough to control weeds in LibertyLink® cotton. In fact, it is the ONLY non-selective post-emergence herbicide that still effectively handles grasses and broadleaf weeds including glyphosate resistant Palmer amaranth, giant ragweed, marestail, waterhemp and kochia. To learn more about how to S.T.O.P. weeds with Liberty, visit for proper application tips.

In addition to the LibertyLink herbicide trait in cotton, growers may choose cotton varieties with a GlyTol® trait, which allows tolerance to glyphosate. Growers who plant FiberMax® or Stoneville® cotton varieties with the GlyTol plus LibertyLink traits can spray glyphosate or Liberty herbicide to control a wide range of tough-to-manage and glyphosate-resistant weeds. While major problem weeds vary by geography, some of the more prominent weed pests controlled include Palmer amaranth (pigweed), marestail, morningglory, Russian thistle and grasses.

Growers should check labels; some older, commercially available FiberMax cotton varieties do not contain both the GlyTol and LibertyLink traits.

Learn more about products Bayer offers to help control weeds in cotton as part of an integrated weed management program.

More Information

You can also find information about Respect the Rotation™, the Bayer resistance management program, at

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