While there are dozens of common weeds that threaten yield each season, many Midwest farmers who grow corn or soybeans are facing off with waterhemp now.
This demanding weed is leading the conversation and building strength against herbicides halfway through 2018. It’s crucial to scout diligently, implement a diverse action plan and use a program herbicide approach with multiple modes of action to combat increasingly resistant waterhemp and other common broadleaf weeds.
“New cases of resistant waterhemp are daunting to those of us in the ag industry because it threatens the already-delicate ROI ratio,” says Dave Roome, customer technical specialist, Corteva Agriscience™, Agriculture Division of DowDuPont. “But waterhemp can grow stronger each year. We have to stay aggressive at reducing the waterhemp seedbank to protect fall yield and get a head start on next season.”
Roome shares five tips to help farmers manage waterhemp for the remainder of this season and to limit additional resistance development:
- Scout diligently. Identify waterhemp early and continue to check your fields now, during midsummer. Ongoing scouting helps farmers plan timely postemergence herbicide applications and identify potential problem fields for the following year. It can be difficult to identify waterhemp in early growth stages because it looks similar to Palmer amaranth and other pigweed species. Waterhemp leaves are generally longer and more lance-shaped than other pigweeds.
- Layer residual herbicides. Layering residual herbicides keeps fields clean longer, typically through crop canopy closure, to manage the waterhemp seedbank. In corn, farmers can apply three unique modes of action with SureStart® II herbicide preemergence followed by an additional unique mode of action from Resicore® herbicide early postemergence. In soybeans, Sonic® herbicide provides two modes of action preemergence followed by DuPont™ EverpreX™ herbicide for an additional mode of action postemergence. Farmers may also add atrazine to their corn programs and glyphosate to corn and soybean programs, in areas where waterhemp isn’t resistant, to increase the number of different modes of action.
- Plant narrower rows. Narrow row spacing can help suppress waterhemp growth by allowing crops to reach canopy closure quicker. Also, tillage is an enemy of waterhemp, Roome says. Tillage can help lower waterhemp populations because the seeds must germinate in the top part of the soil; however, tillage may not be a viable method of control on land prone to erosion.
- Prevent weeds from going to seed. Just a few waterhemp weeds left in a field can present significant problems for the next season. Waterhemp that goes to seed in corn or soybean fields can potentially cross-pollinate with a population in another field and build additional resistance.
- Maximize application technology. Pay close attention to herbicide labels to maximize the efficacy of the product. Not every herbicide can be applied in the same manner with the same nozzles, water volumes, pressures, and adjuvants. Waterhemp requires herbicide control and effective cultural practices, such as rotating crops, which should be planned for more than a single year at a time, Roome says. When rotating crops, think beyond just rotating corn and soybeans to what you can do in that system. Rotating crops also allows farmers to rotate modes of action and adjust tilling plans for corn and soybean fields.