"Most weed management strategies focus on killing the weed plant after it emerges within the crop — few focus on killing the weed before," said Marty Williams, U of I associate professor of crop sciences and USDA-ARS ecologist. "Our research shows the environment in which these weed plants grow has a lasting effect on the seed it produces, and to some degree, the fate of that seed."
In a previous study, Williams' graduate student, Yim So, evaluated how 25 commercial hybrids performed in the presence of weeds. From this large study, So characterized 18 crop traits, then developed a way to boil down these various traits to three factors describing the crop's ability to suppress weeds.
"In a recent analysis, we discovered the first factor from that work accounted for 84 percent of the variation seen in a new experiment with wild-proso millet, one of the most troublesome weeds in sweet corn," Williams said. "Rather than looking at all 18 crop traits individually, we could look at a single factor that described the maternal corn environment — the environment in which escaped wild proso-millet plants are producing seeds."
This allowed the scientists to more accurately relate wild-proso millet responses, such as seed germinability, to crop performance.
"We found that the maternal corn environment influences the development of wild-proso millet seeds. For example, earlier-maturing, shorter corn plants with less leaf area index not only enabled more weed seed production, but they also produced lighter-colored seed," Williams said.
The maternal corn environment also affects how the seed behaves after it is shed from the plant.
"When you have maternal corn environments that allow a lot of wild-proso millet seed to be produced, those seeds are also more likely to germinate soon after dispersal," he said.
So how can this information benefit growers?
Because almost every variety of sweet corn fits a specific niche, poorly competitive varieties are still commonly grown. Some of these varieties are more tolerant to diseases, produce a product with good eating quality, or emerge well under poor conditions, Williams said.
"Economically, growers can only do so much to kill weed plants in the crop," he said. "So it would be helpful if they had additional tools to target other stages of the plant's life cycle. Results from this work suggest there may be new ways to reduce the seedbank of wild-proso millet," Williams said.
For instance, the more germinable seed produced in poorly competitive crop environments could be stimulated to emerge soon after crop harvest, so wild-proso millet could be eradicated post-harvest rather than remaining dormant in the seedbank and causing problems in the future.
Williams said more research is needed to develop and test specific strategies.
"Generally speaking, we need more diversity in how weeds are managed," he said. "Few new herbicides are entering the market, and herbicide resistance continues to erode the effectiveness of current products. Weed management is becoming more complex out of necessity, so folks are thinking broadly about their options."
This study, "Maternal corn environment influences wild-proso millet seed characteristics," was published in Weed Biology and Ecology. The researchers include Marty Williams, Brian Schutte, and Yim So, all of the University of Illinois.
Digital photos available for three months at http://www.aces.uiuc.edu/news/News_Photos/WPM