No. 3 Article 5/April 20, 2012

Soil-Residual Herbicides: Factors Influencing Performance

Soil-residual herbicides are important to integrated weed management programs that allow a crop to become established without weed interference and that reduce the intensity of selection for weed biotypes resistant to particular foliar-applied herbicides. The use of soil-residual herbicides in Illinois corn production has remained relatively consistent over many years, but their use in soybean declined dramatically after the widespread adoption of glyphosate-resistant soybean varieties. In response to the almost exclusive use of glyphosate, the Illinois weed spectrum has evolved, with weed biotypes resistant or less sensitive to glyphosate more and more common. Many farmers are now "rediscovering" the advantages of using soil-residual herbicides in soybean.

However, simply applying a soil-residual herbicide to a field does not guarantee the product will provide the desired level or duration of weed control. Many edaphic (soil) and environmental factors influence the level of control achieved by any particular soil-residual herbicide, and depending on the herbicide, some factors are more important than others.

Weed scientists from the University of Illinois, Southern Illinois University, and Western Illinois University recently produced a new brochure to help farmers better understand the factors that influence the performance of soil-residual herbicides. Revisiting the Realm of Residuals (Adobe PDF, 1.3 MB) identifies how factors that are largely under the control of the end user, such as herbicide selection, application rate, and timing, can impact both the level and duration of weed control. The brochure also highlights the importance of precipitation or mechanical incorporation as mechanisms that place the herbicide into the soil solution, where it needs to be in order to be effective. This publication was made possible with financial support from the Illinois Soybean Association.--Aaron Hager

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