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Getting a Start on Weed Control in the Fall University of Illinois. Urbana, IL (October 8, 2002) - Over the past couple of years, the practice of applying herbicides in the fall to control winter annual weeds has gained widespread popularity. This practice started in fall 1999 in Illinois, with only a few products labeled for fall applications. Since 1999 a number of products have been added to the fall-applied arsenal. With this increase in products has come an increase in interest from many producers. This interest arises mostly from growers who have had a difficult time controlling winter annual and perennial weeds in no-till fields in the spring. Winter annual weeds, such as purple deadnettle, henbit, chickweed, horseweed (marestail), and a number of mustard species, can form a dense weed mat that can be difficult to control with spring burndown herbicides. These difficulties can arise from insufficient spray coverage, fluctuating spring temperatures, and timeliness of the application due to uncooperative spring weather. A number of potential benefits may be realized from controlling winter annual and simple perennial weeds in the fall. Controlling these weeds in the fall prevents dense mats of winter annual weeds that can physically interfere with planting and tillage, reduces vegetation where insects may harbor, and potentially allows for earlier planting due to increases in soil drying and warming. In addition, controlling these weeds in the fall prevents them from producing seed, thereby decreasing the soil seed bank and helping reduce future problems with these species. Fall control of simple perennials, such as dandelions and white cockle, is much more effective than controlling these weeds in the spring. In the fall, food reserves in these perennials are being moved to the roots; when a systemic herbicide is applied, that herbicide moves with the food reserves to the roots and can cause complete control of the roots. Additionally, higher rates of some translocated herbicides (i.e., 2,4-D) can be used in the fall, allowing for greater control of perennial weeds such as dandelion. Fall herbicide treatments can be extremely effective tools in managing winter annual, biennial, and simple perennial weeds. So how do you know if fall herbicide applications are suitable for your farming operation? These applications are most effective on fields where these weeds have been a problem in the past. If spring herbicide treatments have been effectively controlling these species and they do not appear to be increasing, little to no benefit may be gained from fall herbicide applications in these fields. In addition, even though winter annual weeds may be controlled by fall applications, under certain conditions a spring burndown treatment may still be needed. Contacts: Christy Sprague Aaron Hager Ryan Hasty (217) 333-4424 |