With herbicide-resistant weeds appearing on an estimated 70 million acres of U.S. farmland, weed management has become a more complicated job than in the past.
“In Illinois and Iowa, they have some waterhemp populations that have developed resistance to four different site-of-action groups, so it makes it really difficult when you’re trying to think of herbicide groups to manage those,” said Christy Sprague, a professor in Michigan State’s Department of Plant, Soil, and Microbial Science.
Listen to an interview with Dr. Sprague here:
At Farm Journal’s Soybean College in Michigan, Dr. Sprague gave farmers the latest thinking and strategies for tackling difficult weeds like horseweed (also called marestail), waterhemp, and Palmer amaranth in the Midwest.
- Diversify your herbicide use. As resistance grows to glyphosate and ALS inhibitors, farmers need to expand their arsenal of weed-killing weapons to include herbicides with multiple sites of action.
- Know your chemicals. A premix of multiple herbicides won’t help you if the weeds in your fields are resistant to one or more of the active ingredients. Click here for a classification chart that organizes herbicides and premixes by sites of action, brand names, and active ingredients.
- Tillage only goes so far with something like horseweed. “Vertical tillage may not be effective,” said Dr. Sprague. Neither is fall tillage alone. No-till farmers are not immune either, with no-till practices leaving the majority of weed seeds in the top few inches of soil.
- Do a fall or early spring burndown with a combination of herbicides, including a residual product that will provide additional control.
- Pay attention to the calendar. Depending on what herbicides you choose, you may have to wait 7 to 14 days after application until you can plant.
- Consider agronomic options, like planting soybeans in narrow rows at higher populations to reduce the exposure to weeds or use cover crops.
- When harvest comes, take care with weed-infested fields. Avoid them if you can; if you can’t, leave those to the very end. “You don’t want to run those through the combine,” Sprague said.
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What weeds are giving you the most trouble in your fields? What strategies have worked--or failed to work? Let us know in the comments.