INDIANAPOLIS, Ind. — Weeds are relentless year after year, leading farmers, retailers and agronomists across the Midwest to find new ways to control difficult and herbicide-resistant weeds in corn and soybean fields.
“While the weed spectrum hasn’t changed much in recent years, the available methods and level of difficulty to control these weeds has changed,” says Kent Bennis, market development specialist, Dow AgroSciences. “We’re seeing several trends, as part of asound herbicide program, that are helping farmers improve ROI and counter weed pressure.”
To overcome challenging weeds in corn and soybeans, here are three top weed-fighting strategies to keep in mind this season.
Invest in multiple herbicide passes
The timing of herbicide passes is shifting, Bennis says. There are instances when farmers prefer to apply a residual herbicide shortly after planting rather than before. Herbicide timing largely depends on the weed spectrum and density. With increasing herbicide resistance, a two-pass program is the best way to keep weeds small throughout the season.
Identifying waterhemp can be difficult because it looks like Palmer amaranth and other pigweed species in early growth stages.
Commodity prices may tempt farmers to cut down on herbicide passes, but this approach allows weeds to dominate crops before they stand a chance. Uncontrolled weeds can damage yield and profit potential as early as V2 in corn.
To control weeds early – even ahead of planting – farmers can tank-mix burndown herbicides with residual herbicides to plant into a clean field. Dow AgroSciences recently received federal registration from the U.S. Environmental Protection Agency for Elevore herbicide, powered by Arylex active, which can be applied up to 14 days before planting in soybeans and corn. Elevore is tank-mix-compatible with commonly used burndown and residual partners, including 2,4-D and glyphosate, for thorough control of many broadleaf weeds, including marestail up to 8 inches tall.
Layer residual herbicides to extend weed control
Farmers should overlap, or layer, residual herbicides to control tough weeds like Palmer amaranth and waterhemp, which germinate throughout the growing season.
“To prevent weeds from stealing yield and profit, we recommend using a powerful preemergence herbicide to keep weeds small and easier to control,” Bennis says. “This also makes postemergence applications more effective at keeping fields clean through harvest. Farmers can use Resicore or SureStart II herbicide for residual control in corn and Sonic or Surveil herbicide for long-lasting control in soybeans.”
Control pigweeds early before they progress across fields
Waterhemp and Palmer amaranth continue to be driver weeds in corn and soybeans. Waterhemp is slowly taking over more acres each year, Bennis says, and if a farmer is in an area where it was just starting to get bad last year, it’s likely getting worse.
Identifying waterhemp can be difficult because it looks like Palmer amaranth and other pigweed species in early growth stages. The petiole of Palmer amaranth is always longer than the leaf, which is one way to distinguish Palmer amaranth from waterhemp. The first true leaves of waterhemp are generally longer and more lance-shaped than other pigweeds. (1)
In soybeans, farmers can also improve control of tough weeds, including the pigweed species, by planting narrow rows of seven to 15 inches, Bennis says. This allows the crop to shade the row much quicker, which reduces weed germination and emergence.
(1) Nordby, D., B. Hartzler, and K. Bradley. 2007. Biology and Management of Waterhemp. https://www.extension.purdue.edu/extmedia/bp/gwc-13.pdf