Scientists take ecological approach to weeds
UW–Madison researchers have begun a new effort to understand weed-crop competition and to predict corn and soybean yield loss associated with weeds. When completed, the research will help Wisconsin growers manage weeds more efficiently and reduce their reliance on herbicides.
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“During the past 20 years, we’ve spent a lot of time helping farmers remain competitive by providing research results they can use to select and apply chemicals. Now we think we can be most helpful by focusing on weed ecology as it relates to crop production.”
Larry Binning
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Growers face problems with an increasing number of weed species becoming resistant to herbicides, uncertainty over consumer acceptance of crops genetically modified to tolerate herbicides and the potential loss of herbicide options stemming from their review under the Food Quality Protection Act.
Today’s low grain prices are another problem for farmers.
“Growers can manage herbicide costs when crop prices are good,” says Chris Boerboom, who studies weeds in corn. “But when the price of corn falls to $1.50 a bushel and herbicides cost $40 per acre, farmers start looking at input costs more closely.”
Faced with these issues, many farmers are interested in ecologically based weed management strategies. A team of weed scientists from the College of Agricultural and Life Sciences believes that understanding the ecological relationships between weeds and crops is crucial to those new approaches. In addition to Boerboom, the team includes Larry Binning, David Stoltenberg and their students.
To non-farmers the idea of being able to predict if and when weeds will reduce crop yields may sound like a simple one. It’s not.
Weeds are a grower’s most resilient enemy. Weed problems change from year to year depending on the crop and cultivar planted, the time of planting, the weed species present, the weather, the soil type and other factors. More than 100 weed species infest Wisconsin fields. New weed species, such as water hemp, periodically appear in the state. Some weeds emerge early in the growing season, others when crops are planted and still others well after crops are growing.
Since the 1960s, farmers have relied primarily on herbicides to control weeds. Today, herbicides applied to corn, soybean and cotton account for 80 percent of pesticides used on all U.S. crops, according to Binning.
“During the past 20 years, we’ve spent a lot of time helping farmers remain competitive by providing research results they can use to select and apply chemicals,” Binning says. “Now we think we can be most helpful by focusing on weed ecology as it relates to crop production.”
The researchers realize they need to know much more about weeds.
“We lack information on the impact that many weeds have on crops,” says Stoltenberg, an expert on herbicide-resistant weeds. “Our objectives are to quantify the yield losses that weeds cause, and determine why they cause those losses. We want to know the critical periods in the interactions between weeds and crops that determine which plants will be successful. We want to be able to predict when weeds will cause problems and when they won’t.”
“We need to know when we must control weeds so they don’t contribute to the seed bank in soil,” Binning adds. “Weed seeds there can lead to major problems for growers in the following years.”
The researchers also hope to determine how environmental factors — such as temperature, humidity and soil type — affect competition between weeds and the crop.
“Weeds stop growing when the crop canopy reduces light penetration by 96 to 98 percent,” says Binning. “Our general approach is to develop tactics that limit weeds until the crop canopy can prevent further growth. We know this is possible for potatoes and direct-seeded soybeans. However, corn may never reduce light levels that much.”
The crucial period that determines the fate of crops and competing weeds often occurs by the end of May or early June, according to Stoltenberg. But if a weed and soybean plant are the same height on May 15, the researchers can’t now predict which will be the winner.
“The winner will take up more space, light and produce more seed,” Binning says. “The one that lags will devote more energy to growing and catching up to the other, leaving it less energy to produce seeds.”
Because corn doesn’t shade out weeds as well as soybeans, many corn growers also are concerned about late flushes of weeds, Boerboom says. “We need to know how these affect yields and the weed seed bank.”
The team has conducted several studies of lambsquarters and giant foxtail. The two are widespread, very competitive weeds that begin growing in late April and early May, the same time as the crops. The researchers are expanding the studies to examine how multiple weed species interact and affect yields.
The research group also wants to develop a software program for managing weeds based on biological and economic information. It would be a practical tool for growers, consultants and co-ops. As part of that effort the scientists are evaluating the relative competitive ability of eight important weed species in the state.
The work is supported by: state funding to the UW–Madison College of Agricultural and Life Sciences, Hatch grants from the College of Agricultural and Life Sciences, and a grant from the Wisconsin Corn Promotion Board.
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