Kochia, an invasive weed spanning the Great Plains, poses a significant risk to farmland.
Because it lays seeds by becoming a tumbleweed, nearly 100,000 seeds can be dispersed over a large area by one plant. If left uncontrolled, kochia can reduce crop yields up to 60 percent. This risk is made even more pressing when that weed is resistant to herbicides like glyphosate.
Ten states and three Canadian provinces have reported glyphosate-resistant kochia. In Montana, kochia represents the first weed to become resistant to glyphosate.
“Typically, a summer chem-fallow field receives three to four applications of glyphosate before planting of winter wheat in the fall,” said Montana State University weed scientist Prashant Jha. “The enhanced selection pressure from repeated use of glyphosate over years resulted in evolution of glyphosate-resistant kochia populations, with up to 11-fold levels of resistance in Montana.”
Jha, who discovered the resistance of Montana kochia in the fall of 2012, advised growers to use diversified weed control approaches when combating resistant kochia. Using tank mixtures or premixes with multiple effective herbicides on smaller plants or during chem-fallow can be one promising solution to dealing with glyphosate resistance.
Crop rotation, narrow spacing between rows, and strategic irrigation are some other methods of controlling resistant kochia, Jha suggested.
“One of the important aspects of preventing further spread of glyphosate-resistant kochia in Montana farm and ranchlands is to effectively manage kochia in roadsides, ditch banks, fence lines, and field borders,” added Jha.
Sugar beets are under extra risk, as few herbicide options other than glyphosate are available. This has placed more evolutionary pressure on kochia to adapt to that particular pesticide, and increased the speed at which resistance develops. Because of this, Jha encouraged sugar beet growers to adopt a “zero tolerance” policy toward kochia seeds.