Managing weeds and herbicide resistance has become a year-round necessity for farmers. It starts in the spring with an herbicide plan including overlapping chemistries to provide broad-spectrum protection pre and post planting. Fall is an opportunity to evaluate overall herbicide effectiveness and determine if a burndown strategy is needed to keep fields clean.

OSU Professor Mark Loux has spent more than 30 years studying weeds, conducting research and offering insights to farmers to help protect their yields.

According to Loux, most farmers need to build their herbicide programs around the “Big Five:” Palmer amaranth, waterhemp, marestail and giant and common ragweed. While many of these emerge in the spring and summer, marestail can also emerge in early fall and survive into spring, making for a more difficult preplant burndown situation.

Loux offers these tips to farmers dealing with late-season weeds and considering burndown applications.

  1. Scout Fields. Spend some time scouting soybean fields in August and September prior to harvest. This helps farmers identify potential new issues and determine a plan of action before jumping in the combine.

“Knowing what’s out there gives farmers a better understanding of how their herbicides performed and whether or not they need to adjust their plans moving forward,” said Loux. “One of our main reasons for this recommendation is to prevent new infestations of waterhemp and Palmer amaranth, since stopping seed production by these weeds is step number one in prevention.”

  1. Treat With Cost-Effective Options in the Fall. According to Loux, farmers shouldn’t spend a lot on fall burndown herbicides to treat problem areas. A good mix can be purchased for about $5-$8 per acre and may be able to provide additional residual control into spring on certain weeds.

“2,4-D is a good base chemistry to eliminate marestail. Add in others such as dicamba, Basis®or glyphosate to broaden the spectrum. Canopy products for soybeans add another layer of protection that can last into later spring on some weeds, but not marestail,” said Loux.

  1. Understand Seed Spread. Weed seeds can spread in ways farmers may not think about. Flooding can carry seeds to different areas of fields. Sometimes people providing custom combine services or spreading manure can unknowingly transport weed seeds from other farms.

“It’s always good to ask the people who deliver products and services to your farm, where they’ve come from and make sure they’re aware of how seeds can spread,” said Loux. “Livestock producers who don’t grow crops might not realize that certain feed products can transport weeds.”

  1. Plan Ahead. After harvest wraps, it’s time to take another look at the herbicide program. Determine what worked, what didn’t and talk with dealers about making adjustments for the next growing season. Farmers should also make sure they’re rotating traits and herbicide sites of action, so they don’t overuse certain chemistries, which can lead to resistant weeds.

Looking for more resources to enhance your weed management plans? Loux recommends the following sites:

Back to Research

Sign up to receive our newsletter.