Kochia control in March and early spring is essential
Producers soon should begin planning their program for controlling kochia. The spread of glyphosate-resistant kochia populations throughout western Kansas, and the difficulty growers have had controlling these populations, suggest perhaps control measures should begin prior to emergence of kochia.
Large flushes of kochia emerge in March and April. If allowed to emerge, post-emergence herbicide applications often will not provide complete control. Incomplete control of these dense populations might result because the kochia is glyphosate resistant and complete herbicide coverage is not possible. The dense populations also might be stressed, which reduces the effectiveness of post-emergence applications.
The choice of herbicides for effective pre-emergence control of kochia in March will vary depending on subsequent cropping intentions. This article will discuss fields going to sorghum or corn this spring and wheat this fall. Cropping scenarios are discussed below.
Going to corn, sorghum
For fields that will be planted to corn and sorghum this spring, a combination of glyphosate (using a minimum of 0.75 pounds/acre) with herbicides that have pre- and post-activity on kochia are most valuable. Tank mixing 8 to 16 ounces of dicamba or 1 to 2 pints of atrazine will control small kochia, and other existing broadleaf and grass weeds, and will provide extended pre-emergence control into May. An application of Clarity alone suggests a pint provides better control than 8 ounces; however, a combination of atrazine and Clarity is better than Clarity alone. If producers wait until later so they can apply the burndown and pre-emergence herbicide in the same application, the kochia will be larger and most likely will not be controlled. If that occurs, the surviving plants will go on to cause problems throughout the growing season.
Other herbicides that could be tank-mixed with the glyphosate ahead of corn or sorghum include Lexar EZ or Lumax EZ, or for corn only 3 to 4 fluid ounces of Corvus or Balance Flexx. The addition of atrazine is key for most effective control. The addition of Banvel did not increase kochia control with Corvus+atrazine or Balance Flexx+atrazine in 2012. When marginal rainfall is received for the initial activation, Banvel, which is soluble, is able to be activated and provide significant kochia control while atrazine and other herbicides might not be activated.
Going to wheat this fall
If kochia is emerging in row crop stubble intended to be planted to wheat this fall, herbicide options exist that provide residual kochia control. Atrazine cannot be used in this situation, as the treatment is off-label. The following herbicides could provide effective residual control of kochia for fields to be planted to wheat this fall: Dicamba, metribuzin or Dimetric (Dimetric label indicates half to two-thirds of a pound), Corvus, Balance Flexx or Lumax. These products allow wheat to be planted four months following application.
Note: To see the full article and accompanying charts of research data (herbicide control) and kochia control in other crop scenarios (sunflowers, soybeans and kochia in standing wheat) go to www.agronomy.ksu.edu/extension, then click onto Extension Agronomy e-Update on the right-hand menu tab.
The data is from irrigated plots at the K-State Southwest Research-Extension Center at Tribune, and with populations of kochia that are susceptible to triazines.
* This article and the accompanying research data came from Curtis Thompson and Dallas Peterson, K-State Research & Extension Weed Management Specialists.
Stacy Campbell is Ellis County agricultural agent with Kansas State Research and Extension.