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Extension Web site helps farmers rein in horseweed

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Written Friday, December 10, 2004  

A new Purdue University Web page offers farmers general information and educational materials on dealing with horseweed, a plant that is infesting parts of Indiana's cropland.

Horseweed, also known as marestail, has become a major weed control issue in parts of southern and central Indiana, said Bill Johnson, Extension weed specialist. Horseweed is predominantly found in no-tillage crop systems and targets soybeans, corn, wheat and nurseries.

For more information on horseweed and to locate areas where horseweed is glyphosate-resistant, producers, agribusiness specialists and interested individuals can visit the new Purdue horseweed science Web site at http://www.btny.purdue.edu/weedscience/marestail/index.htm .

"The big problem with horseweed in specific areas is that many populations are resistant to the herbicide glyphosate used in Roundup Ready soybean production," Johnson said.

Johnson said that horseweed competes with crops for moisture, nutrients and light. Horseweed also can serve as a host to Aster-yellows, which is a disease that interferes with harvest and provides unwanted foreign material in the grain.

The first case of glyphosate resistance in Indiana was confirmed in Jackson County in 2002, Johnson said.

"Since 90 percent of the soybean acres in Indiana are planted to Roundup Ready varieties and 60 percent of soybeans grown utilize no-till practices, it is very important to find the best alternatives to help keep horseweed from becoming an even bigger problem and threat to production agriculture in Indiana," he said.

Purdue experts advise farmers concerned about horseweed to use alternative herbicides and/or tillage to control plants before planting soybeans. Weeds less than six inches tall are much easier to control than larger plants. The key is to not plant soybeans in fields with live horseweed. To fight the horseweed infestation, Johnson recommends the use of other herbicides such as 2,4-D; dicamba; FirstRate; Classic; Sencor; Python; Valor; and Authority as preplant herbicides.

If the weed is already present in fields, Johnson said that the only effective way to treat the problem is with the addition of FirstRate or Classic to glyphosate. However, these herbicides will not be effective if the population also is resistant to these herbicides as well, he said.

The Web site was created by Purdue weed science Extension specialists to provide information on the distribution, biology and management of glyphosate-resistant horseweed in Indiana and other affected states. The site includes maps of Indiana and surrounding states with confirmed areas that have glyphosate-resistant horseweed and areas that are currently being researched and sampled.

The site frequently updates maps showing locations of glyphosate-resistant horseweed and the latest research results on the biology and management of the weed.

Funding for this research and Extension project was provided by the Indiana Soybean Board, U.S. Department of Agriculture's Critical and Emerging Pest Program, Purdue University Ag Research Programs, Monsanto, Syngenta, Dow Agrosciences, BASF, Valent and Dupont.

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