Maximizing the Value of Soil-Applied Herbicides

	Bill Simmons Associate Professor Dept. of Natural Resources and Environmental Sciences (217) 333-9649; fsimmons@illinois.edu
		Loyd Wax Professor Department of Crop Sciences, USDA/ARS (217) 333-4424; l-wax@illinois.edu

Soil-applied herbicides and postemergence herbicides with soil activity are important parts of many weed control programs. Glyphosate-tolerant soybean cultivars have allowed for successful weed control with the use of various glyphosate products, often with no help from other herbicides. Soil-active herbicides may be a valuable tool for delaying the application of glyphosate until closer to canopy closure or for reducing weed emergence following a glyphosate application.

Two current topics of study are:

the use of soil-applied herbicides in a fall application to reduce the growth of winter annuals preceding no-till corn and soybean planting, and
the effect of application timing of glyphosate alone or mixed with imazethapyr or imazaquin on weed control and soybean yield.

Figure 1. A field with a fall application of simazine.

Studies assessing application timing of several soil-applied grass herbicides in corn show that each herbicide has an optimal range of application date. If producers elect to apply these herbicides more than 30 days in advance of planting, selection of herbicide and herbicide formulation become important.

Some fall-applied grass herbicides have shown effectiveness roughly equivalent to a 60-day early preplant application in northern Illinois. In central and southern Illinois, application closer to planting usually is a better practice.

Figure 2. A field without a fall application of simazine.

Recent warm winter seasons combined with wet springs have confronted no-till producers with excessive weed biomass at planting time that may interfere with planting. Fall-applied herbicides to suppress the growth of winter annuals in both corn and soybean fields is being studied in southern Illinois.

Soil-applied herbicides remain a valuable tool in corn and soybean weed control. To achieve the maximum value of these herbicides, producers must optimize application timing and adjust practices to fit the weed spectrum, while minimizing the potential for adverse crop response.

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Department of Crop Sciences
College of Agriculture, Consumer and Environmental Sciences
University of Illinois Extension