Harvest is the best time to reflect on the 2016 growing season and plan for weed management in 2017. Indiana corn and soybean growers saw rapidly changing weather this year, which led to some difficult weed management issues they’ll want to address for the next growing season.
“We saw a cool, wet spring, which was a challenge for farmers. Planting got off to a slow start and rain made spring herbicide applications difficult. Now we are seeing areas where giant ragweed and waterhemp weren’t controlled early and those mature weeds are likely to make harvest more difficult,” says central Indiana DuPont Crop Protection Technical Sales Agronomist Don Matthes.
Adding to grower concerns, marestail, waterhemp, giant ragweed and Palmer amaranth populations are developing resistance to common herbicides, making them hard to manage with traditional weed-control programs.
Do You Know Your Weeds?
Palmer amaranth has migrated north to Indiana, Illinois and Iowa in recent years. It’s hard to control due to its aggressive growth, prolific seed production and ability to quickly adapt to weed management tactics. Glyphosate-resistant Palmer amaranth varieties have been a concern for growers in the southern U.S. for several years and are now becoming a problem for Midwestern growers.
Identifying and treating weeds when they are small is critical for both good control and resistance management, but that’s when identification is most difficult. Palmer amaranth and waterhemp can be especially tricky to tell apart. In general, Palmer amaranth has wider, broader leaves than waterhemp, which has longer, more tapered leaves. Also look for the V-shaped purple or white watermark occasionally found on Palmer amaranth leaves.
Control Giant Ragweed Early
Giant ragweed germinates early and grows fast, so it easily competes with crops for light, nutrients and moisture. Giant ragweed plants towering over tasseled corn in some fields this season points out plants that weren’t controlled by postemergence herbicide passes earlier this year.
Experts recommend applying a postemergence herbicide before giant ragweed plants are 4 inches tall for best control. “Too often, growers miss the window for controlling giant ragweed because they wait for other weeds to emerge,” says Matthes. A season-long program that uses overlapping residual herbicides with multiple modes of action will help fill those gaps.
Late-Emerging Marestail in 2016
Marestail tops the list of problem weeds for Midwest growers. Seeds usually germinate in fall or spring, but marestail can germinate in late summer with the right conditions.
Marestail plants that germinate in the fall overwinter as rosettes and begin growing again in the early spring, quickly generating seeds and adding to the weed seed bank. The rosette stage is the best time for herbicide application and the best way to keep populations under control.
Best Practices for Resistant Weeds
Better weed management begins with understanding what happened this season, then identifying a control program that begins as soon as the combine leaves the field.
“Multiple modes of action are the best management tool against the spread of resistant weeds,” says Matthes. “Ideally, use a fall burndown herbicide and plan a preemergence or at-plant residual herbicide application next season.” Tillage and rotating crops from year to year are other management practices that help manage hard-to-control weeds.
Stretch Input Dollars
DuPont is offering growers added financial benefits in 2017 with the TruChoice® Early Pay Multiplier program. The program lets growers multiply their crop protection dollars up front, then make final crop protection decisions when they purchase products from their DuPont retailers.
Contact your local DuPont agronomist or retailer to learn more about the TruChoice® Early Pay Multiplier program and customized weed-control solutions that will help deliver peak performance from every acre in 2017.
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