PPO-Resistant Palmer Pigweed Control Strategies

Soybean yield depends on good weed control, especially if PPO-resistant Palmer amaranth is present.

Herbicide-resistant weeds continue to threaten soybean yield potential. Many growers who have traditionally relied on ALS, glyphosate and PPO-inhibitor herbicides aren’t seeing the weed control they expect. As of late 2016, according to the University of Arkansas, PPO-resistant Palmer amaranth had been documented in seven states, including Arkansas, Illinois, Indiana, Kentucky. Mississippi, Missouri and Tennessee.

The University of Arkansas conducted trials in 2016 to evaluate weed-control programs for PPO-resistant Palmer amaranth. Key learnings from the research indicated the most effective control was achieved with timely herbicide applications and layering multiple modes of action with residual and contact herbicides.

Areas With PPO-Resistant Palmer Amaranth

By early 2017, seven states had documented PPO-resistant Palmer amaranth populations.

Start Clean to Boost Benefits

Having an effective preemergence treatment in place is critical for effective weed control, especially in the face of PPO-resistant weeds. Planting into clean fields helps at-planting and postemergence herbicides work more effectively and also leads to more even stands for better canopy closure.

Experts agree that a multi-pass herbicide program with multiple modes of action is the best bet against resistant weeds. “Unfortunately, there’s no easy button to push to manage resistant weeds,” says Dickie Edmund, DuPont Crop Protection field development representative. “Based on the results of the University of Arkansas trials, DuPont Crop Protection has a lot of options for programs that provide good weed control.”

DuPont™ Trivence® herbicide was one of the herbicides in the top soybean preemergence treatments in the trial. It delivers three modes of action for control of broadleaf weeds, including Palmer amaranth, waterhemp, marestail, giant ragweed and lambsquarters. Trivence® can be mixed with additional metribuzin or pyroxasulfone to enhance broadleaf weed control (recommended for control of PPO-resistant weeds), with pendimethalin or pyroxasulfone for grass control or with DuPont™ Abundit® Edge herbicide (glyphosate) and/or 2,4-D for broad-spectrum burndown before planting. Check the Trivence® label for details on tank-mix partners and mixing instructions.

Take a Program Approach

“Managing resistant weeds is not about an individual product. It’s about a program approach based on each grower’s weed-control needs,” says Edmund. “In areas where there is concern about PPO resistance, we recommend adding Zidua in the tank mix with Trivence® to deliver an effective second mode of action.”

Researchers found that DuPont™ Canopy® herbicide tank-mixed with DuPont™ Cinch® herbicide or Boundary herbicide also provided good preemergence control against PPO-resistant Palmer amaranth, with each set providing two effective modes of action.

Edmund advises growers to review their weed management strategies and make adjustments where weeds have escaped control. He points out that if resistance is suspected, but not yet confirmed, fields should be treated as if they contain resistant weeds.

This comprehensive management strategy can help control Palmer amaranth: DuPont™ LeadOff® herbicide or Canopy® for burndown, followed by an at-planting application of Trivence® (plus Zidua if PPO-resistant weeds are an issue) for residual control. An early postemergence herbicide application should be applied by 21 days after planting and should target pigweed no larger than 2 inches in height to be effective. Multiple postemergence applications will likely be required for PPO-resistant Palmer amaranth, especially in high-pressure areas.

In addition to a comprehensive herbicide program, cultural practices including planting early and choosing soybean varieties with fast emergence can help fend off weeds. Early emergence allows soybeans to get started before weeds germinate. An added bonus is that extra spring moisture can provide a more suitable environment for germinating soybeans and also helps activate at-planting herbicides for better weed control.

The information provided on this website is for reference only. Always refer to the product labels for complete details and directions for use.