Strategic weed control needed for pigweed

Linda Benedict  |  9/11/2012 7:58:33 PM

ALEXANDRIA, La. – A herbicide-resistant weed in soybeans and cotton has caused what an LSU AgCenter weed scientist calls an epidemic in Louisiana.

“This is the year of the pigweed,” Daniel Stephenson told farmers gathered for the field day on July 19 at the LSU AgCenter Dean Lee Research and Extension Station.

The hardy weed, also known as Palmer amaranth, which is native to the Southwest desert, was first documented as glyphosate- resistant in Louisiana in 2009 in Concordia Parish. Then, in 2010, the problem was identified in Tensas and Madison parishes, which are north of Concordia.

Though 2011 was quiet, the problem has exploded in 2012, Stephenson said, and now resistant pigweed can be found throughout the northeast region and is rapidly spreading to other parts of the state.

The remedy is a diversified weed control management program, which includes use of residual herbicides applied preplant, at planting and in-season, Stephenson said.

“Crop yield is determined early in the season,” Stephenson said, adding that farmers can’t allow weeds to outcompete the crop for sunlight, water, nutrients and space.

Herbicides should include products with different modes of action as a means to manage resistance development, which has occurred because of long-term use of glyphosate, or Roundup herbicide, Stephenson said.

Treat not only the field, but also turn rows and drainage ditches because the weeds that grow there produce seed as well, Stephenson said.

When pigweed plants are too tall for herbicides to kill, the only remedy is handpulling, Stephenson said. 

Linda Foster Benedict

(This article was published in the summer 2012 issue of Louisiana Agriculture magazine.)

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