Kochia control in corn and grain sorghum
Producers should start this winter in planning their program for controlling kochia in corn and grain sorghum. The spread of glyphosate-resistant kochia populations throughout western Kansas, and the difficultly growers have had controlling these populations, suggest that perhaps control measure should begin prior to emergence of kochia.
Huge flushes of kochia emerge in late March and into April. Applying 16 oz/acre of Clarity/Banvel/generic dicamba with a pound of atrazine around mid-March, before the kochia has emerged, could provide significant control of early flushes of kochia. The addition of 2,4-D will help control winter annual mustards that have emerged. This will make subsequent kochia control measures discussed in this article more effective. When treating kochia with burndown or in-crop herbicides, spray early when the plants are about 1 to 3 inches tall.
Control in corn
Kochia control in corn should always include a burndown application in April, shortly after the first kochia has emerged. A combination of glyphosate and dicamba will control small kochia, and almost all other existing weeds and grasses, at that time. If producers wait until later so they can apply the burndown and preemergence herbicide in the same application, the kochia will be larger and they may not get complete kochia control. If that occurs, the surviving plants will go on to cause problems throughout the growing season. Tillage prior to planting in a conventional till system can also be very effective.
The label for Clarity states that no more than 32 oz/acre can be applied per season. If 8-16 oz/acre is applied in March as an early preplant and 8 oz/acre is applied as a burndown ahead of corn or sorghum planting that still allows for an 8 oz application in-crop, which is often more than what is used in-crop.
After the early April burndown treatment, the next step would be to use a preemergence herbicide. Atrazine, or a product containing atrazine, should be included with this application. Even if there are triazine-resistant populations of kochia present, atrazine will still help control a number of other weed species.
Good options to include in a preemergence application for control of kochia (and other weeds) include:
* A chloroacetamide/atrazine premix. Examples of chloroacetamide-atrazine premixes include Bicep II Magnum, Cinch ATZ, Guardsman Max, Propel ATZ, Bullet, Harness Xtra, Keystone, Volley ATZ, FulTime, and others. New options in this class of herbicides that could be used include Zidua and Anthem plus atrazine or Anthem ATZ, which has atrazine included. The active ingredient, pyroxasulfone, in these herbicides has the best activity on kochia of the choroacetamides. If triazine-resistant kochia is present, then one of the other options below would be the better choice.