Jumpstart Your 2022 Weed Control This Fall
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Kicking off your corn and soybean weed control programs this fall can give you a head start on problem weeds for the 2022 growing season.
University weed scientists often cite herbicide-resistant marestail (horseweed) as a prime target, because fall application offers better control compared to spring when marestail is taller. “If you can spray emerged marestail with a higher rate of 2,4-D in the fall, you’ll almost always see better results at planting compared to trying to control overwintered and often larger plants with lower 2,4-D rates in the spring,” says Aaron Hager, University of Illinois weed scientist.
Another good fit for fall-applied weed control is in minimum or no-till fields where chickweed, henbit, shepherd’s purse, dandelion and other winter annuals, biennials or perennials show increased populations. Also, prevented planting fields or areas that missed in-season herbicide applications due to weather are prime fall application candidates.
Marestail and some winter annual weed seeds lack dormancy, which can lead to an immediate increase in fall-emerging weeds. Therefore, weed scouting before, during and after harvest can determine where and when fall herbicides pay dividends.
Residual or Non-Residual Weed Control?
There is often debate on whether to include a residual herbicide in a fall tank-mix because it's difficult to predict the weather and soil conditions. Most Midwest growers tend to skip the residual to focus their weed control budget on effective spring preemergence and postemergence applications.
“If an early October application is possible when annual weeds are still emerging, a residual herbicide can offer benefit,” Hager says. “However, the majority of later applications into November don’t need a soil-residual herbicide because the winter annuals have emerged and can be controlled with non-residual herbicides.”
Residual herbicides applied in the fall are subject to a quicker breakdown if a mild winter occurs. On the other hand, a cold, harsh winter can create the potential for carryover. “Just don’t use a residual product in the fall thinking you’ll get control of spring-emerging annual weeds; it won’t happen,” Hager adds.
“If an early October application is possible when annual weeds are still emerging, a residual herbicide can offer benefit,” Hager says. “However, the majority of later applications into November don’t need a soil-residual herbicide because the winter annuals have emerged and can be controlled with non-residual herbicides.”
Simplicity and Timing
A typical fall burndown tank-mix is often a combination of glyphosate with 2,4-D or dicamba to control weeds that have already emerged. Atrazine might be another option if you plan to plant corn or sorghum in 2022.
The goal is a weed-free seedbed going into April. By applying a fall burndown, a spring residual herbicide application just has to control small weeds that emerge before planting. The other side benefit of a fall application is less potential for drift problems on sensitive targets.
Fall application timing comes down to weed emergence. If it's dry, wait for rain and additional weed emergence before application. Refer to the herbicide labels for details on temperature as some products work better in warmer conditions (60 degrees), while others can thrive in the 40- to 50-degree range.
At cooler temperatures, absorption and translocation of glyphosate and 2,4-D are lower, so control takes longer. If temperatures are below 40 degrees for prolonged periods after application, weed control is reduced. Spraying after a hard frost isn’t usually advised.
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