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Early-Season Weed Control in Corn

May 4, 2001
With the warm, dry weather over the last couple of weeks, corn planting has progressed dramatically, and corn appears to be emerging in good condition. In many cases, with the push to get all of the corn crop planted and the extreme winds that have plagued us over the last few weeks, it has been very difficult to get soil-applied herbicides sprayed in a timely fashion. This has left many growers and applicators with the decision on what to do for weed-management strategies on those acres that haven't been treated and the corn crop has emerged. There are essentially two different approaches a grower has in this situation. The first option is to use the soil-applied herbicide program that was initially plan-ned, and the second option is to switch to a total postemergence strategy.

In examining the first option of using a delayed application of a soil-applied herbicide, several factors should be considered. Many, but not all, soil-applied corn herbicides can be applied after corn emergence. Keep in mind that not all of these herbicides will control emerged weeds. Additionally, there are a number of soil-applied herbicides that can cause significant crop injury if they are applied after corn emergence. So in some instances additional management strategies may need to be implemented to control existing vegetation. These strategies could include the use of a rotary hoe or the addition of a herbicide that has postemergence activity. Table 2 contains information about which "traditional" soil-applied corn herbicides can be applied postemergence and some considerations to remember if these herbicides are applied to emerged corn. For additional information consult the respective product labels.

If considering the option of switching to a total postemergence herbicide program, there are also some points that should be addressed. First, there are a number of good postemergence corn herbicide options available to growers, and information on these products can be found in chapter 2 of the Illinois Agricultural Pest Management Handbook. However, a number of these herbicides do not provide any soil-residual control, and often the timing of herbicide application is critical for providing season-long weed control. The second point to consider is that while we often stress a maximum corn height or developmental stage for postemergence herbicide applications, some postemergence corn herbicide labels indicate a minimum size or developmental stage the corn should be at before an application is made. This is a particularly important consideration when deciding on a postemergence herbicide program when corn is in its early developmental stages. Table 3 lists the postemergence corn herbicides that have minimum corn size label restrictions. So remember that there are a number of considerations that need to be made when deciding on weed-management strategies for early-season corn.--Christy Sprague and Aaron Hager

Author: Aaron Hager Christy Sprague

The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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