Strategize for Problem Weeds

Combine planning, technology and flexibility to overcome weed control obstacles.
Strategize for Problem Weeds
Preemergent residual herbicides, such as Boundary 6.5 EC, and post-emergent herbicides, such as Tavium Plus VaporGrip Technology, are important technologies in a proactive weed control plan.
“When I started farming 25 years ago, cocklebur and johnsongrass were our main problems,” says Brad Outland, a farmer in Hopkinsville, Kentucky, who raises corn, soybeans and wheat. “Today, we fight glyphosate-resistant marestail and pigweed in soybeans, while johnsongrass continues to be an issue in corn and soybeans.”

Herbicide-resistant weeds and seed trait technology influence his plans each year. Outland develops field-specific weed control programs to effectively protect yields that require step-by-step planning based on the crop to be planted.

Identify Weed Problems

“The first step is knowing which weeds are most problematic,” says Bill Johnson, Ph.D., professor at Purdue University. “Farmers usually target one or two major weeds, but they also need to know the next five or six species in a field to build a program that handles the entire spectrum.”

Prashant Jha, Ph.D., extension weed specialist for Iowa State University, recommends also considering herbicide performance over the past five years. Noting weeds that survived past treatments helps farmers understand weed seed banks.

You can develop a good weed control program, or you can get a cheap weed control program. It’s hard to get both. If you spend less, you’ll control fewer weeds.

Josh Bailey
Marketing Manager
Nutrien Ag Solutions
Researchers and ag retailers emphasize scouting throughout the season to identify more prevalent, harder-to-control weeds:
  • Early-season scouting confirms weed spectrum.
  • Following each herbicide application, scout to monitor performance.
  • Scouting throughout and at the end of season can catch late-emerging weeds or escapes that may produce seed.
  • After harvest or frost, walking fields reveals weeds likely to cause problems next season.
Select Chemistries and Traits

Johnson expects weed identification to be critical for 2022. He recommends residual herbicides as a plan’s backbone, bearing most of the weed control pressure. Then post-emergence herbicides clean up escapes.

Josh Bailey, marketing manager for Nutrien Ag Solutions based in Hopkinsville, Kentucky, believes that farmers will need trait platforms with multiple post-applied options this season.

“With weed control, you get what you pay for,” he says. “You can develop a good weed control program, or you can get a cheap weed control program. It’s hard to get both. If you spend less, you’ll control fewer weeds.”

Bailey recommends using multiple modes of action and overlapping residuals in every crop. He views any weed that emerges as an escape.

“The easiest way to control a weed is to never let it come up,” he says.

As a farmer, Outland relies on his agronomist for scouting. He picks trait packages compatible with chemistries likely to knock out resistant weeds and prefers herbicides containing three modes of action, especially in corn.

Mark Kitt, Syngenta technical product lead for corn herbicides, says a sound two-pass weed resistance management program in glyphosate-tolerant corn starts with Lexar® EZ or Lumax® EZ herbicides applied preemergence, followed by Acuron® GT herbicide applied post-emergence to weeds less than 4 inches tall.

“To manage resistant weeds, use products like Acuron GT, which contain active ingredients with multiple effective sites of action to control targeted species. Acuron GT uses three sites of action and four active ingredients for knockdown and residual control of tough weeds,” Kitt says.

In soybeans, Boundary® 6.5 EC, BroadAxe® XC and Prefix® herbicides each contain two complementary active ingredients that provide preemergence control of annual grasses and small-seed broadleaf weeds, such as waterhemp and Palmer amaranth, according to Pete Eure, Syngenta technical product lead for soybean herbicides.

“Following this with Tavium® Plus VaporGrip® Technology in dicamba-tolerant soybeans or tank-mixing Sequence® herbicide in other systems delivers overlapping residuals, increasing the level of control,” Eure says.

Diversify Weed Control Strategies

Crop rotation, tillage, row spacing and cover crops help manage tough weeds. Some crops, such as corn, have more herbicide options for resistant weeds. Using multiple modes of action in different crops supports herbicide stewardship.

Jha explains that scientific research at Iowa State University demonstrates benefits of cultural and mechanical practices for controlling resistant waterhemp. In trials, a high-biomass cereal rye cover crop planted before soybeans reduced waterhemp emergence 30% to 40%, while 15-inch soybean row spacing cut its emergence 15% to 20%.

Jha is also studying aggressive harvest weed seed control strategies to reduce weed seed banks. Chaff lining uses a combine attachment to separate soybean straw and chaff. Most weed seeds stay in the chaff, deposited in a narrow windrow behind the combine. This concentrates the area for weed control next season.

“Seed destructors also attach to combines,” Jha says. “They capture and pulverize about 65% of weed seeds, significantly reducing the seed bank.”

With a clear understanding of the weed spectrum and tools available, farmers can customize programs by field to successfully control weeds. Investing in residuals and accurate application, along with agronomic practices, will improve seasonal and long-term results.

“Every operation is unique, and no solutions are one-size-fits-all, but every operation can find a cultural practice that fits,” Johnson says, “whether that’s a more advanced practice like a seed destructor or chaff lining, or simply focusing on waterways, field borders and entries.

“Farmers need programs with diverse weed control strategies,” Johnson continues. “Treating herbicides like natural resources that must be used wisely will prevent us from exhausting their benefits.”

Combine planning, technology and flexibility to overcome #weedcontrol obstacles. Explore the different strategies.

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