It makes sense that if weeds can't get a lot of sun, they won't be able to grow as well. Marty Williams, an ecologist with USDA's Agricultural Research Service in the College of Agricultural, Consumer and Environmental Sciences at the University of Illinois, used this premise as he began his search for sweet corn hybrids that have the ability to naturally suppress weeds.

"There aren't a lot of tools for weed management in sweet corn, so I decided to look at the inherent characteristics in different hybrids that might help reduce some weeds naturally," Williams said. "Using a more competitive hybrid -- one that naturally suppresses weeds - means farmers can use less herbicide and get more consistent crop yields."

Test plots from 2004 show in the foreground wild proso millet and the dramatic difference in the canopies of three sweet corn hybrids in the background: GH2547, left; Spirit, center; WH2801, right.

For his study, Williams chose three commercially available sweet corn hybrids that have different canopies in order to determine how the density of the canopy might affect weed growth. He chose Spirit, WH2801 and GH2547. "Unfortunately, it's not practical to do this study for every hybrid. There are just too many," said Williams. "But what we hope to do is eventually get enough information to classify hybrids as competitive or not competitive in weeds."

Wild pros millet was grown at low, medium, and high weed densities within the sweet corn hybrids. This particular weed was chosen because it is one of the fastest-spreading annual grass weeds in the cornbelt and it's a significant problem because few herbicides are effective against it in sweet corn.

Last year's results showed that Spirit, a hybrid with little canopy, had a 70 percent yield loss at high weed pressure. It didn't tolerate weeds very well at all. WH2801, which was taller, faired better in its ability to suppress weeds while maintaining a high yield. GH2547, which had the largest canopy, did even better at both. "And, since it managed to suppress weed seed production better, there would be fewer weeds emerging next year in that field," said Williams.

The same experiment is being conducted now to see if the results are consistent under drier conditions observed this year.

In Illinois, processed sweet corn sold in cans or frozen in bags or on the cob is a significant commodity. Illinois, Wisconsin and Minnesota supply about half of the sweet corn for processing in the United States. Washington State provides the other half. Rick Boydston, with USDA-ARS at Prosser, Washington is duplicating Williams' canopy experiment. "The results from Dr. Boydston's first year were similar but not as dramatic as ours here in Illinois. Any differences in the ability of hybrids to suppress weeds are important, since every bit helps," said Williams.

This study is focusing on yield and weed suppression, but yield isn't the only consideration. What about the sweet corn sugar content, taste, and appearance? In another one of Williams' research projects, he is looking at about a dozen different quality traits and determining how they are affected by the weeds. "For example, the number of ears is important for fresh market sweet corn - what you find in the produce aisle - whereas kernel weight is extremely important for sweet corn grown for processing - what you buy in the can," said Williams. "Since eradicating every weed in sweet corn is impractical, we need to know exactly how weeds - particularly at low densities - influence these traits."

Author: Debra Levey Larson