AG NEWS
AG NEWS

Combating Weed Challenges in Corn for 2017

  • Mar 01, 2017
Corn leaves
Midwest corn fields saw their share of weed issues during 2016; however, farmers have more herbicide options available to keep fields clean and manage resistance. Depending on the location, leading problem weeds in 2016 included resistant ragweed (common and giant), waterhemp, cocklebur and morning-glory (see state recaps below). 
 
With similar weed issues reported in both corn and soybean fields, a holistic management approach across all crops in a rotation is needed. Increasing resistant weed numbers calls for a complete herbicide-resistance management program that starts with a clean field at planting. Other recommended steps include crop rotation, three effective modes of action, overlapping residuals, timely applications and use of full-label herbicide rates accompanied by complementary adjuvants.
 
WinField United agronomists recently shared some corn weed insights from 2016 in this Corn & Soybean Digest article. Highlights by state are below.
 
Illinois: Giant ragweed, cocklebur and morningglory presented challenges for Illinois corn farmers in 2016, Glenn Longabaugh notes. Although weather affected herbicide performance, many corn weed problems were due to using a single-pass herbicide program, stand voids and continuous use of single site/mode of action. For best results, Longabaugh recommends using two-pass programs that include effective residual herbicides. He also advises avoiding the temptation to reduce costs in 2017 by cutting residual herbicides, since the small savings gained are not worth the risk of a weed-control disaster.
 
Indiana: Giant ragweed and other large-seeded broadleaves proved to be the greatest weed challenge for Indiana corn farmers in 2016, says George Watters. Overall, growers were able to manage resistant species in corn due to having several effective herbicide groups available. Premixes and/or other combinations of growth regulators (Group 4), triazines (Group 5), shoot inhibitors (Group 15) and HPPDs (Group 27) can still work well, Watters notes. For best results, he recommends starting with a burndown application or tillage, followed by a residual herbicide program close to planting and followed again by a sequential postemergence treatment. Some farmers have also had good results with split-applying their residual herbicides.  
 
Iowa: Ryan Wolf says Iowa corn growers continued to deal with glyphosate-resistant waterhemp issues in 2016, while glyphosate-resistant giant ragweed also became a bigger issue. As farmers become more aware of resistance issues, Wolf says they are adjusting their weed control programs accordingly. He advises farmers that keeping weeds in check now will help avoid bigger, more costly problems in the future.  
 
Michigan: There weren’t any major weed-control issues to report in Michigan’s corn fields during 2016, says Allen Pung. He attributes this favorable weed-management scenario to the fact that the majority of farmers in his area are using an effective preemergence weed-control program followed by an in-season herbicide application.
 
Minnesota: Giant ragweed and tall waterhemp were the two major weeds in Minnesota cornfields in 2016, reports Al Bertelsen. These two weeds have produced a large seed bank in both corn and soybean fields, causing widespread issues. Both weeds can germinate over long periods of time. This lengthy germination period may outlast many soil-applied herbicides and allow weeds to escape late in the season after the herbicide application window has passed. Bertelsen urges farmers to scout corn later in the season for weed escapes and to control weeds when they are small. Controlling weeds in drowned-out spots will help lower weed seed banks and decrease weed pressure in future years, he says.
 
Ohio: Joe Rickard identified giant ragweed, which starts to emerge in early spring, as the biggest weed issue in corn in Ohio during 2016. He notes that while weed resistance is not as widespread in corn as it is in soybeans, there are some pockets of resistance in Ohio fields.
 
South Dakota: Glyphosate-resistant waterhemp is presenting challenges in South Dakota corn fields, reports Ryan Wolf. However, as farmers are becoming more aware of the issue, they’re adjusting weed-control programs accordingly. Wolf notes that while some farmers may be hesitant to spend the additional money needed to control resistant weeds now, keeping weeds in check will help avoid even bigger, more costly problems in the future.  
 
Wisconsin: Todd Cardwell saw high populations of common and giant ragweed in Wisconsin corn fields in 2016, which was likely due to an unusually wet season. There was also a growing population of triazine-resistant weeds, making atrazine treatments less effective than they have been in previous years. Cardwell says farmers had successful weed control in no-till fields using burndown applications in the fall, which made in-season treatments more effective. With a different weed spectrum in reduced-till or no-till environments, fall applications are very cost-effective. He notes that every dollar spent on weed control in the fall is worth at least $7 in the spring.

For similar insights on Soybean weed challenges, click here.