Using a herbicide that injures the corn plant along with the weeds pretty much defeats the purpose of using a selective herbicide, not to mention being extremely costly for farmers. Although herbicides are intended to kill only the weeds, some corn hybrids are sensitive to certain herbicides, particularly in sweet corn.  This herbicide-induced injury ranges from temporary symptoms, such as stunting or leaf damage, to permanent damage including yield loss, and in severe cases, crop death.

"Several herbicides currently registered or being considered for use in sweet corn have the potential to injure specific hybrids.  The herbicide label may say something like, 'check with your seed dealer for hybrids to use with this product,'" said Dean Riechers, a weed scientist in the College of Agricultural, Consumer and Environmental Sciences at the University of Illinois. Riechers said that the seed companies often feel the herbicide manufacturers are responsible for knowing how their products affect the crop, yet herbicide manufacturers don't necessarily have access to all seed materials. The U of I can provide not only an unbiased test to find out which hybrids are sensitive to herbicides, but uncover the underlying reason why these hybrids are injured by herbicides.

"It's ironic that some sweet corn hybrids are severely injured by what's supposed to help them," said Marty Williams, an ecologist with USDA's Agricultural Research Service and collaborator on the project. "But then obviously there are other hybrids that tolerate herbicides completely.  We want to know more about this herbicide sensitivity trait, including how it is inherited."  Such knowledge will enable corn breeders to identify sensitivity to herbicides at early generations in the breeding programs and allow herbicide manufacturers to construct pesticide labels that more fully address the risk of using these chemicals.

Riechers and Williams, along with University of Illinois's sweet corn geneticist Jerald "Snook" Pataky, are doing exactly that.  They started by evaluating hundreds of sweet corn hybrids and inbreds, looking for lines that were sensitive to several herbicides.  While conducting this work, Pataky made experimental corn lines derived from a cross of two sweet corn inbreds: one tolerant and one sensitive to the herbicides.  "These lines, and additional corn lines we are creating from them, provide exactly the material we need to determine the inheritance of sensitivity to these herbicides," said Pataky.

Aside from identifying sensitive hybrids and inbreds, what have they found?  "There is an association between sensitivity to Accent and Callisto," said Pataky.  "Most hybrids, inbreds, and experimental lines sensitive to Accent were sensitive to Callisto, and those tolerant to Accent were often tolerant to Callisto."  This outcome, along with additional evidence, indicates that a single recessive gene conditions sensitivity to both herbicides. While follow-up research is ongoing, this knowledge has important implications for seed companies and herbicide manufacturers. "Weeds are a serious threat in every field, every year, so having selective tools for weed management is critical," said Riechers.  "Everyone benefits, especially farmers, when the crop does well following a herbicide application."

A portion of this research was supported by funding from the Midwest Food Processors Association, Crookham Company, and Illinois Foundation Seeds, Inc.