10/19/01

Contacts:
Christy Sprague, University of Illinois, (217) 333-9652
Tracy Petersen, Iowa State University Agriculture Communications, (515) 294-0706

RESEARCH: HERBICIDES DO NOT WORSEN COMMON SOYBEAN DISEASES

URBANA, Ill. -- Preliminary greenhouse studies with soybeans indicate that herbicide applications do not worsen three common soybean diseases.

Two University of Illinois researchers are studying interactions among herbicides, diseases and soybean varieties as a part of a multistate effort to understand factors limiting soybean yields. The project also involves scientists at Iowa State University, the University of Wisconsin and Southern Illinois University.

The Illinois study is led by Christy Sprague, assistant professor of weed science, and Loyd Wax, professor of weed science and a USDA Agricultural Research Service collaborator.

The concept of studying these interactions arose from the first three years of the yields project, Sprague said. Scientists had observed that diseases seemed to be more severe when herbicides were applied to soybeans known to be infected with Rhizoctonia. Injury to the plants also was visible.

For the current study, Sprague and Wax chose to work in the greenhouse. "With field research, you're always chasing the disease," Sprague said. "You may not always get the disease you want. You may not be in the right field or the weather may not be correct for the disease. The greenhouse gives us the ability to control the environment."

The researchers are working with Savoy and Jack, two public soybean varieties. They are looking at how the varieties stand up to soybean cyst nematode (SCN), sudden death syndrome (SDS) and Rhizoctonia when treated with herbicides. The herbicides are Raptor and Flexstar.

In preliminary results related to Rhizoctonia, Sprague and Wax have found the herbicides do not adversely affect soybeans infected with the disease. Soybeans were more susceptible when they were inoculated with Rhizoctonia early rather than later. Raptor applications to the Jack variety appeared to decrease the severity of Rhizoctonia. Savoy was slightly less susceptible to Rhizoctonia than Jack.

In early results on the herbicides' effects on SCN and SDS, it appeared that the Raptor herbicide decreased cyst production when applied to the Savoy variety. (The Jack variety is resistant to SCN.) There also appeared to be no effect on plant growth when the herbicides were applied to soybeans infected with SDS.

Work will continue on SDS, SCN and Rhizoctonia interactions with different herbicides. "We'll also examine the effect of herbicides on susceptible and tolerant Roundup-Ready soybean lines," Sprague said. "After that, we plan to look at interactions of multiple diseases."

Until further research results are in, Sprague did not recommend that farmers change their weed and disease management strategies.

Sprague and Wax's research is part of the Yields Project, a multistate research program funded by Iowa and Illinois checkoff dollars through the Soybean Research and Development Council (SRDC). The Yields Project is one of the largest soybean research projects ever undertaken to understand factors that limit soybean yields.

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