With the grain harvest progressing on or ahead of schedule in most parts of Indiana, no-till producers should start thinking now about their fall herbicide applications, a Purdue Extension weed specialist says. The focus this year should be on managing marestail, dandelion and poison hemlock in corn and soybean fields, said Bill Johnson, professor of weed science. “With all the rain we had earlier in the year, we didn’t really get a good crop canopy, and a crop canopy helps to suppress weeds later in the season,” Johnson said. “In many areas, poor canopy development resulted in a lot of late season weeds.”
The timing of the fall herbicide application is important as is the choice of product. “Most of the weeds farmers are likely to encounter in the fall respond better to a fall application,” Johnson said. “In most cases, a properly timed application of foliar herbicides such as glyphosate, 2,4-D and/or dicamba from mid-October to mid-November will control weeds that emerged this fall. It also will result in fields having lower densities of smaller weeds next spring. Those smaller weeds can be more easily controlled with a spring burndown than in fields that did not receive a fall burndown.”
Farmers should be cautious, however, about residual herbicides. “If farmers want to spray now, with warm and sunny conditions, then using residuals could have some benefit,” Johnson said. “But if they are planning to wait a month, and we have colder conditions, it would be better to avoid the residuals because they simply won’t do any good if no weed emergence occurs after application.”
He recommends applying the residuals as close to spring planting as possible for control of next year’s summer annual weeds and limiting the fall application to foliar products that treat the weeds that are already in the fields.