University of Missouri researchers have confirmed that tall waterhemp is the sixth glyphosate-resistant weed in the
Kevin Bradley, a
Glyphosate is the active ingredient in Roundup herbicide. The fields where resistant waterhemp was found had been in continuous Roundup Ready soybean production since 1996.
While all resistant weeds are worrisome, Bradley says resistant tall waterhemp is especially troubling. "Waterhemp is one of
"If the resistant trait is carried in the pollen, which we are fairly confident it is, then you have pollen traveling to fields all around the resistant plants," Bradley adds. Each female waterhemp plant produces hundreds of thousands of seeds, ensuring a ready supply of plants for the following season.
Bradley and Legleiter have found good news in their field plots. The glyphosate-resistant waterhemp is killed by a number of popular pre-emergence soybean and corn herbicides. Bradley reported on this strategy at the Weed Resistance Management Field Day June 20 near
The pair plan at least two seasons of examining whether the resistant plants can be brought under control economically in continuous soybeans - using pre-emergence and post-emergence herbicides - or whether it is better for farmers facing resistant weeds to alternate plantings of corn and soybeans. The rotation opens up a wider array of herbicides labeled for use in corn.
The eight other confirmed glyphosate-resistant weeds throughout the world include common ragweed, buckhorn plantain, goosegrass, hairy fleabane, horseweed (a.k.a. marestail), Italian ryegrass, palmer amaranth and rigid ryegrass.