North Louisiana farmers who used herbicide for several years running on fields of "Roundup Ready" plants are now beset by a weed that the chemical cannot control.
The LSU AgCenter says tests confirm herbicide-resistant pigweed in three fields in north Louisiana - cotton fields in Tensas and Franklin parishes, and a soybean field in Tensas Parish.
The cotton and soybeans are genetically engineered to be resistant to the herbicide glyphosate (GLY-foh-sate). The weeds get that way naturally.
AgCenter weed scientist Jim Griffin says weeds that survive the herbicide produce seeds that grow into more plants that can also survive it.
Resistant pigweed was found last year in Concordia Parish, and resistant johnsongrass was found in Pointe Coupee Parish.
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