Herbicide-resistant Weeds Among Topics Featured At LSU AgCenter Field Day

Donnie Miller  |  6/17/2006 12:16:13 AM

Roy Vidrine, professor at the LSU AgCenter’s Dean Lee Research Station near Alexandria, addresses a group during the AgCenter’s Northeast Research Station field day Wednesday (June 15) at St. Joseph. Vidrine told field day participants about work the AgCenter is doing related to weeds showing resistance to various herbicides.

News Release Distributed 06/16/06

Nearly 200 farmers and other agricultural industry representatives were on hand Wednesday (June 14) for the annual field at the LSU AgCenter’s Northeast Research Station at St. Joseph.

The half-day program featured stops at 10 field locations where LSU AgCenter scientists explained their research with row crops and how it can help Louisiana farmers.

One topic that’s generating interest among growers and researchers is weeds becoming resistant to glyphosate, a popular nonselective herbicide that can kill any plant it contacts.

Now, farmers are finding plants in their fields that have survived glyphosate treatment. When they come across these plants, LSU AgCenter researcher Dr. Donnie Miller collects the seeds from the plants and grows them to see if they produce plants resistant to the herbicide. The resistance has to be passed to the next generation for the plants to be truly resistant, he explained.

Miller, an associate professor at the LSU AgCenter’s Northeast Research Station, said no confirmed weed resistance to glyphosate has been found in plants in Louisiana. He said because farmers are getting rid of easy-to-control weeds, they are just finding plants that are more difficult to kill.

Along those same lines, researchers are evaluating Roundup Ready volunteer cotton and soybeans, which are plants that grew from seeds left in the field following the prior year’s harvest. These seeds are from plants that have been developed to be resistant to glyphosate so that herbicide could be used to control weeds in those crops.

Researchers consider soybean plants in cotton fields and cotton plants in soybean fields as weeds. Because both kinds of plants are broadleaf, most herbicides that would kill the "weed" also kill would the crop plant. But because these descendants of Roundup Ready plants also would be resistant to glyphosate, another tactic has to be used to manage the "weed."

Farmers have to control these glyphosate-resistant plants early, Miller said. "They can be a very tough weed once they get going," he said.

Volunteer cotton also can be a host to boll weevils, and volunteer soybeans can harbor Asian soybean rust – if those plants aren’t eliminated.

While the boll weevil eradication program has been making progress in eliminating the insect pest from Louisiana cotton fields, Asian soybean rust is a disease that’s a looming threat to Louisiana soybean fields.

Although the fungus that causes the rust has been identified in limited areas of Louisiana the past two falls, it hasn’t appeared in commercial fields early enough in a season to cause crop damage.

Dr. Boyd Padgett, an associate professor at the LSU AgCenter’s Macon Ridge Research Station in Winnsboro, explained how the AgCenter is monitoring Asian soybean rust with sentinel plots – where researchers collect leaves, incubate them and then examine them for signs of Asian soybean rust.

The LSU AgCenter is maintaining 15 of these sentinel plots in the state, he said.

Dr. Charles Overstreet, a professor in the LSU AgCenter’s Department of Plant Pathology and Crop Physiology, told about research using global positioning equipment to develop site-specific methods for applying fungicides in particular parts of soybean and cotton fields where nematodes – small, microscopic worms that feed on plant roots – are most likely to cause problems.

Overstreet also said planting sorghum in rotation with cotton or soybeans is good for controlling reniform and root knot nematodes, while a rotation with corn can help control reniform nematodes. He also said soil texture appears to be an indicator for identifying areas of fields where nematodes may be more active.

Maurice Wolcott, a research associate in the same department, said using global positioning technology has shown that nematodes in light-textured soils cause the greatest yield loss and that nutrient deficiency appears to be involved. He said researchers are trying to mitigate nematode damage by changing fertilizer application rates in those particular areas of a field using planting and fertilizer application equipment outfitted with global positioning technology.

Also at the field day, LSU AgCenter entomologist Dr. Ralph Bagwell talked about tarnished plant bug and aphid control in cotton.

He said the tarnished plant bug is the No. 1 insect problem in cotton in Louisiana. He recommended alternating insecticides, using higher volumes of water in insecticide applications and selecting sprayer tips that provide extensive coverage of the material on plant leaves.

In another report, Dr. Bill Williams, an associate professor at the LSU AgCenter’s Northeast Research Station, said pre-plant weed control is most important in corn.

"Early weed control helps insect control," he said. He recommended having the weeds gone two weeks before planting.

Other presentations at the field day included discussions on aflatoxin, corn fertilization, precision agriculture and soybean planting dates.

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Contacts:
Donnie Miller at (318) 766-3769 or dmiller@agcenter.lsu.edu
Boyd Padgett at (318) 435-2157 or bpadgett@agcenter.lsu.edu
Charles Overstreet at (225) 578-2186 or coverstreet@agcenter.lsu.edu
Ralph Bagwell at (318) 435-2908 or rbagwell@agcenter.lsu.edu
Bill Williams at (318) 766-3769 or bwilliams@agcenter.lsu.edu
Writer:
Rick Bogren at (225) 578-5839 or rbogren@agcenter.lsu.edu

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