July 18, 2006

Study explores long-term effectiveness of herbicide

by K.C. Jaehnig

CARBONDALE, Ill. -- Concerned that wily weeds may evolve their way past one of farming's cheapest and simplest weed killers, university scientists from six states are banding together to conduct the largest-ever study of Roundup Ready cropping systems.

Underwritten by chemical manufacturing giant Monsanto, which makes the popular herbicide, the study will last four years, involve 25 to 30 40-acre fields in Illinois, Indiana, Iowa, Nebraska, North Carolina and Mississippi and cost $5.28 million.

"The biggest question weed scientists are dealing with now is can we gain any information on how long we have with glyphosate (the active ingredient in Roundup) before weeds adapt to current Roundup Ready cropping systems — that's what's on growers' minds," said Southern Illinois University Carbondale's Bryan G. Young, who heads the Illinois portion of the study.

"If we have to add another herbicide to glyphosate (to make it more effective), then it's no longer as cheap and simple as it once was."

The sheer number of acres involved in the research should up the odds on spotting changes in weed populations.

"Whenever you talk about weed resistance to herbicides, it's a numbers game," said Young, a weed scientist in SIUC's College of Agricultural Sciences.

"If you're doing research with a typical small-plot design — one acre or less — you're not very likely to find that one out of a million, billion or trillion weeds that may be resistant to glyphosate. With a very large research area, you increase your chances of observing a rare or unique event."

The project got under way last fall with a telephone survey conducted by a professional polling service of farmers in the six states who had used Roundup Ready crops. The survey yielded data on not only on their herbicide use but on tillage practices, crop rotation strategies and weed management problems, too.

"This provided the historical data that we could use to identify trends," Young said.

The researchers then approached some 100 of these growers in each state about participating in the larger study. In Illinois, 24 farmers are registering 27 fields — from Rochelle to McClure, Danville to Astoria — in the study. Some grow Roundup Ready soybeans continuously, some combine those beans with Roundup Ready corn, while others grow Roundup Ready beans with regular corn.

"In our state, these are the three most common rotations," Young said. "Other states may use other crops, like cotton."

Using global positioning system technology to ensure they always monitor the same spots in each field, researchers will take soil samples and conduct weed counts. The soil samples, taken before planting, will help them estimate the number of weed seeds in the field. The weed counts, performed at planting, two weeks after the last treatment with post-emergence weed killer and again before harvest, will give them a handle on both weed numbers and weed species.

In addition, researchers will divide each field in half. Growers will manage their halves in their usual manner. Researchers will experiment with management practices for the other sides.

"We want to identify the best management practices that will keep glyphosate effective over the long term," Young said.

Finally, the scientists will take a look at both yields and the cost of management in each half.

"We might have marvelous ideas, but if the cost is prohibitive, chances are growers won't implement them," Young said.

Leading in research, scholarly and creative activities is among the goals of Southern at 150: Building Excellence Through Commitment, the blueprint the University is following as it approaches its 150th anniversary in 2019.