Fighting Back against Prolific Weed Resistance

managing resistance in soybean fields

For as long as growers have battled weeds in their fields, weeds have fought back. Nature continues to be resilient and has proven, time and again, that there is no single solution to manage tough-to-control and resistant weeds.

Weed resistance has continued to expand over the years, with resistant weed species now found in all major field crops, including corn and soybeans. In some cases, individual weed species have developed resistance to multiple sites of action.

Resistant weeds that are known to be very aggressive in the Midwest include waterhemp, marestail, lambsquarters, and common and giant ragweed. These are often referred to as "driver weeds" since they alone can make some fields unfit for growing corn and soybeans.

The Latest Research: Tankmix Sites of Action

Recent university research indicates that growers can control weeds and manage resistance by tankmixing more than two effective sites of action. The difference was significant. “A field in which 2.5 MOA per application were used was 83 times less likely to select glyphosate-resistant waterhemp within 4-6 years than a field in which only 1.5 MOA per application were used.”1

Talk to a specialist about recommendations for your farm. Consider the history of weeds in your fields, and choose a chemistry with no resistance to those weeds.

The History of Resistant Weed Evolution

Herbicide-resistant weeds were first discovered in the United States in the late 1960s in a pine nursery, where triazine herbicides had been used repeatedly. Triazine resistance continued to spread and was the most widely recognized type of weed resistance for several decades.

During the early- to mid-1980s, a new ALS site of action chemistry was introduced into wheat and later other crops. Because of their low use rates and effectiveness against labeled weeds in wheat, growers quickly adopted ALS herbicides, applying them year after year.

After four to five years of use, however, growers began to observe prickly lettuce and kochia escaping from ALS herbicide treatments. After four additional years, ALS-resistant weeds were widespread across the western United States.

Bayer has a broad portfolio to combat tough-to-control and resistant weeds. A well-thought-out herbicide program, using multiple effective sites of action, should be implemented to sustainably manage weeds.

Bayer Solutions for Corn Growers

When managing corn crops for high yields, remember it’s always best to start with a clean field. The following program can help you manage weeds in your cornfields:

  • Start with an Autumn™ Super (2) application in the fall.
  • The following spring use Corvus® (2, 27), a pre-emergence residual herbicide that has overlapping sites of action to control early-season problem weeds.** 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.
  • The second pass should include a postemergence product, such as DiFlexx® DUO (4, 27) or Liberty® (10) herbicide.

Another pre-emergent herbicide Bayer 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 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® (2, 27) postemergence herbicide delivers season-long control of more than 65 grasses and broadleaves, including those resistant to glyphosate, PPO, ALS, dicamba and triazines.

Manage Weeds in Soybeans

Bayer 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® soybeans.

Liberty herbicide has a unique site of action and no known resistance, making it an excellent resistance management tool that can be tankmixed with other approved sites of action. Liberty is the only postemergence herbicide that still effectively handles resistant weeds, including grasses, broadleaf weeds and glyphosate-resistant weeds.*

*Corvus and Balance Flexx are restricted use pesticides.

**The active ingredient in Liberty is a Group 10 herbicide, which is the only broad-spectrum herbicide that effectively controls grasses and broadleaf weeds, and it has no known resistance in U.S. broadacre crops.

Work Cited

1. Hager, Aaron. “Slowing the Evolution of Weed Resistance to Herbicides.” The Bulletin, University of Illinois Extension. April 2015.
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