Soil-residual herbicides are important components of integrated weed management programs, according to University of Illinois associate professor of weed science Aaron Hager. “They can allow the crop to become established without weed interference and reduce the intensity of selection for weed biotypes resistant to particular foliar-applied herbicides,” he said.
 
Their use in Illinois corn production has remained relatively consistent over many years. By contrast, their use in soybean dramatically declined following the widespread adoption of glyphosate-resistant soybean varieties.
 
However, the Illinois weed spectrum has evolved in response to the almost exclusive use of glyphosate post-emergence in soybean, and weed biotypes resistant or less sensitive to glyphosate are becoming increasingly common. Many farmers are now rediscovering the advantages of using of soil-residual herbicides in soybean.
 
Simply applying a soil-residual herbicide to a field does not guarantee that the product will provide the desired level or duration of weed control. “Many edaphic and environmental factors influence the level of weed control achieved by any particular soil-residual herbicide,” said Hager, “and, depending on the herbicide, some factors can be even more important than others.”
 
To help farmers understand these factors, weed scientists from the University of Illinois, Southern Illinois University, and Western Illinois University recently produced a new brochure, “Revisiting the Realm of Residuals.” Publication was made possible by financial support from the Illinois Soybean Association.
 
The brochure explains how factors that the end user can largely control, such as herbicide selection, application rate, and timing, can impact both the level and duration of weed control. It also highlights the importance of precipitation or mechanical incorporation as mechanisms that place the herbicide into the soil solution where it needs to be to be effective.
 
A PDF of the brochure is available at:
http://www.nsrl.illinois.edu/production/multimedia/Residual%20Herbicides%202012.pdf .