Fighting kochia poses challenge due to glyphosate resistance
Glyphosate-resistant kochia is becoming more common in northern South Dakota between the Missouri River and Highway 281. This could become a challenging weed in Roundup Ready soybeans as there are few effective postemergence herbicides available.
Cobra (lactofen) may be the most effective alternative herbicide, but Cobra can cause severe soybean leaf burn, which does not cause yield loss but is often not desirable. Therefore, effective preemergence herbicides, such as Valor (flumioxazin) or several of the Authority (sulfentrazone) products, must be used.
Considering these limitations, it may be more convenient to plant LibertyLink soybeans to control glyphosate-resistant kochia. Ignite (glufosinate) used in LibertyLink soybeans is often less consistent than glyphosate, but South Dakota State University trials have demonstrated that two-pass LibertyLink herbicide programs can be very effective and consistent.
Crop rotations can be a significant part of glyphosate-resistant kochia management. Aggressively managing kochia in rotation crops such as small grains could quickly reduce kochia densities. Kochia seed is highly viable and has almost no dormancy. Therefore, seed banks may be greatly reduced after only two to three years of aggressive management.
To do this, it will be important to get almost complete kochia control as one plant can produce 15,000 to 25,000 seeds. In addition, maintaining no-till practices will ensure that viable seed stays near the soil surface, whereas tillage may bury viable seed, causing it to remain in the soil until it is unearthed again in subsequent years, which will delay seed bank depletion.
Depleting the kochia seed bank could enable the continued use of Roundup Ready soybeans as one preemergence herbicide application may be enough to control low kochia densities.
The SDSU Extension weeds program is conducting field research as part of a regional effort with neighboring states to explore the viability of this approach.
Mike Moechnig, SDSU Extension weed specialist
This article published in the May, 2012 edition of DAKOTA FARMER.