- Associated Press - Sunday, April 20, 2014

ALEXANDRIA, La. (AP) - LSU AgCenter scientists say Italian ryegrass found in Louisiana has developed resistance to herbicide.

Daniel Stephenson said seed from fields in Tensas Parish was used to grow the plant and confirm its resistance to glyphosate.

Italian ryegrass is widespread in northeast Louisiana and has been found in St. Landry Parish to the southwest, Stephenson said.

The weed can rob a corn plant of 75 percent of its yield. It also poses a problem for cotton and soybeans because clumps of dead Italian ryegrass can interfere with planting and seedling growth.

A fall application of the alternative herbicide Dual Magnum is the best way to control it, Stephenson says, but the usual treatment of glyphosate and 2,4-D won’t kill it. Dual Magnum also suppresses the weed henbit, he said.

AgCenter scientist Donnie Miller said Italian ryegrass - even if it’s not herbicide-resistant, is a problem for row crops. “It’s going to suck moisture out of the seedbed,” Miller said.

Because it is a winter annual, the weed could cause problems for wheat, Miller said. “It competes directly with the crop.”

In addition, Italian ryegrass seed can be comingled at harvest with wheat grain, causing quality issues when a crop is sold, Miller said.

Stephenson said the plant emerges in September and October. It emerges again in January.

He said farmers who neglect to treat the weed in the fall will pay more in the form of additional herbicide treatments in the spring before planting.

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