Farmer Wrestles with Resistant Weeds in Sensitive Watershed

Garry Niemeyer was excited to see glyphosate-tolerant soybeans come to market for use with the contact herbicide in the mid-1990s. Since his Auburn, Illinois, farm is located in the Lake Springfield watershed, he saw immediate advantages versus soil-applied chemicals.

“Being able to use glyphosate in soybeans, and then corn, was a real plus for us. We used it on everything,” says Niemeyer, who has 1,800 acres of the crops in a 50-50 rotation. He also raised seed beans for 40 years. “But after a while, I learned you need to break up your chemicals.”

Loss of Control Creeping In

Niemeyer first experienced a break in control with waterhemp about five years ago, followed by some loss of control on horseweed, common ragweed, velvetleaf and lambsquarters. 

“Glyphosate was no longer controlling these weeds like it used to, so we upped the rate and that worked for a few years,” he says. “I discussed the potential weed resistance with our agronomist, and we made some changes in 2018 and 2019 to include dicamba in our herbicide strategy.”

He selected an herbicide trait seed with tolerance to both glyphosate and dicamba. Niemeyer also included other modes of action in his applications while still employing his usual routine of working down cornstalks in the spring. He followed planting with up to three passes of herbicides, fungicides, fertilizers and micronutrients. 

Niemeyer describes his process: “I switched up my strategy. I sprayed one pass of sulfur and an herbicide premix with three sites of action: saflufenacil (group 14), imazethapyr (group 2) and pyroxasulfone (group 15). We field-cultivated those chemicals in and later used a post-application of glyphosate (group 9) and dimethenamid-p (group 15). Dicamba (group 4) was added on fields that bordered corn or dicamba-tolerant soybeans or had tall waterhemp. The third pass included a fungicide, micronutrients and a small amount of nitrogen.”

Multiple Modes for Better Control

Adding dicamba to the mix of modes of action managed Niemeyer’s troublesome weed spectrum. He did not see any harmful impact on soybean yield, either. In 2018, he averaged 95 bushels per acre on 900 acres of soybeans and averaged 74.35 bushels per acre in 2019.

“I attribute that to weather in 2019, which made it worse for herbicide performance,” he says. “A wet July or August brings higher yields, but you may see late, bigger-seeded weeds depending on your earlier treatment program. I had better weed control with multiple modes of action.”

This year, Niemeyer is likely to use the same herbicide program since he had good luck with it in 2019. “I like to plant multiple seed brands of Roundup Ready 2 Xtend soybeans in the 2.8-3.6 maturities,” he says. “You can’t just go all glyphosate for weed control anymore.”

Niemeyer also plans to maintain a vigilant scouting schedule. He checks for weeds once a week until fields are sprayed in mid-May and then checks every three days.

“It definitely pays to scout. No new chemicals are coming, so we have to make do with what we have and preserve their effectiveness,” he says. “I hope the new technology that allows you to spray individual weeds will help stall weed resistance. There is still time to adopt good practices.”

The content in this document was last updated 7/30/2020. As details continue to emerge and change for farmers regarding 2020 dicamba over-the-top applications in soybeans, Take Action is committed to providing unbiased articles and researcher-vetted resources to help navigate this growing season. Find the most updated dicamba information at iwilltakeaction.com/dicamba-resources.