Source: University of Illinois

Years ago it was very common for most corn and soybean acres in Illinois to be treated with one or more soil-residual herbicides before crop and weed emergence. During the 1980s, commercialization of broad-spectrum, postemergence herbicides began the shift away from widespread use of soil-residual herbicides; products such as Basagran, Classic, Accent and Pursuit contributed to the early adoption of postemergence weed control programs. The era of total postemergence weed control reached its zenith following the widespread adoption of glyphosate-resistant crops and the concomitant use of glyphosate. However, "recent" changes in weed spectrums and an increasing frequency of weed populations resistant to glyphosate have heralded a shift back to soil-residual herbicides, especially in soybean.

Soil-residual herbicides can provide many weed management benefits, but several factors influence their effectiveness. Product selection, application rate, and timing of application in relation to crop planting are largely under the control of the farmer, whereas soil moisture at application and the interval between application and the first precipitation event are largely not. A few considerations and suggestions for improving the effectiveness of soil-residual herbicides are provided here. 

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