4 Steps: Managing Resistant Palmer Amaranth, Boosting Yield

Effectively manage resistant palmer amaranth by establishing a consistent soybean growing advantage.

The Delta region is ground zero for the rapid expansion of resistant Palmer amaranth. Speaking to Southern crop consultants, Dickie Edmund, DuPont Crop Protection field development representative, noted resistant pigweed is estimated to have dense populations in two-thirds of the region as of 2016. Most populations had been resistant to both glyphosate and ALS for several seasons before that, with PPO resistance becoming widespread in 2015.

“An effective management plan takes a systems approach to give soybeans a consistent growing advantage,” says Edmund. “And growers should know the plan starts before planting begins.”

Follow these four steps to manage resistant Palmer amaranth and maximize soybean production:

Step 1. Start Clean

“Timing is everything. Palmer amaranth weeds are voracious competitors for natural resources and quickly outgrow soybean seedlings,” said Edmund. “The first key is to reduce early season competition, since a clean, weed-free field at planting gives soybeans a head start on the resource race.”

The easiest ways to achieve clean seedbeds are tillage and/or an effective burndown treatment. Burndown residual herbicides such as DuPont™ Canopy® EX, LeadOff® and Afforia® deliver contact plus extended residual control to manage winter annual weeds. A good seedbed frees crops from competing for sun, water and nutrients. And it makes herbicide applications more effective with better contact on target weed leaves. Planting restrictions vary by burndown program, so be aware of preplant intervals and plan ahead.

Step 2.    Plant Early

The goal is for soybeans to germinate well ahead of weeds. Palmer amaranth plants can grow 2 to 3 inches per day, so a more mature soybean crop stands a better chance of competing with fast-growing weeds than crops that germinate at the same time as weeds. And better moisture conditions in the spring can mean better early season crop growth.

“Growers who know or suspect the presence of PPO-resistant Palmer amaranth in their fields should plant LibertyLink soybeans,” Edmund advised. “The trait provides the opportunity for postemergence use of an effective mode of action in-crop.”

Step 3.    Speed up Canopy Closure

“With or without PPO-resistant Palmer amaranth, it pays to choose aggressive soybean varieties,” he added. “Combined with a clean seedbed and early planting, rapid canopy closure gives soybeans the chance to block out weeds. A weed that can’t reach sunlight has less chance of robbing yield, no matter how resistant it is.”

Narrow row spacing helps with quick canopy closure. Best practice calls for a minimum of twin rows on 38-inch beds, said Edmund.

Step 4.    Overlap Residuals

Effective weed management comes from herbicides with strong contact and residual control that eliminate existing Palmer amaranth and prolong the advantage of a clean field for young soybean plants. Multiple modes of action are key here, making DuPont™ Canopy® and Trivence® herbicides excellent preemergence options for early season weed control in soybeans.

“Postemergence application timing is critical for effective Palmer amaranth control. Herbicide efficacy dramatically decreases after Palmer amaranth plants reach 3 inches in height,” said Edmund. “Without exception, postemergence applications should take place 14 to 21 days after planting and include multiple modes of action.”

Postemergence options that offer contact and residual control are limited. In LibertyLink soybeans, apply Liberty plus Prefix or metolachlor. In glyphosate-tolerant soybeans, glyphosate plus Prefix timed very early postemergence is the only option, according to Edmund.

The information provided on this website is for reference only. Always read and follow all label directions and precautions for use.
DuPont™ Afforia®, Canopy®, Canopy® EX, LeadOff®, Synchrony® XP and Trivence® may not be available in all states. See your local DuPont sales representative or retailer for details on availability.
Liberty® and LibertyLink® (Bayer). Prefix® (Syngenta).