Getting kochia under control in any cropping system that includes wheat begins with the wheat crop during the spring, and shortly after wheat harvest. This is not always easy, even if an application of dicamba had been made before jointing to control kochia present at that time.
Later-emerging kochia in wheat
Although a majority of kochia emerges early in the spring, some emergence can extend over a period of weeks or months. A herbicide applied early in the spring will need to have residual activity to be effective on later-emerging kochia. Several ALS-inhibitor herbicides have good residual activity, but are ineffective on ALS-resistant kochia.
Dicamba, a non-ALS herbicide and one of the more effective products on most populations of kochia, must be applied before the jointing stage of wheat, meaning that later-emerging plants may not be controlled.
Most other non-ALS herbicides that can be applied at a later growth stage of wheat are primarily contact herbicides that require thorough coverage to be effective, and this can be difficult to achieve when the wheat canopy gets larger and covers up some of the kochia present. Two exceptions are Huskie and Starane. Those two products can be applied at later growth stages of wheat, are translocated (Starane more so than Huskie), and are effective on kochia.
Control in wheat stubble after harvest
If kochia has not been completely controlled in the wheat crop, then it may be present at the time wheat is harvested. In most cases, the kochia plants will have grown taller than the wheat canopy and will get “topped” by the combine as the wheat is harvested.
If kochia has been topped, producers should wait until some regrowth has occurred before applying herbicides in the wheat stubble to control it. A combination of glyphosate plus either dicamba or Starane may be the most effective treatments to control kochia in wheat stubble. Even if kochia populations are resistant to glyphosate, the tank-mix combinations with dicamba or Starane will probably provide good control, as long as the kochia aren’t too big or stressed. Some 2,4-D can be added to the mixture to help with control of other broadleaf weeds, although 2,4-D generally will not help much in controlling kochia.
An alternative option would be to treat the kochia with Gramoxone. Gramoxone activity will be increased if applied with atrazine. However, only corn or sorghum may be planted the following spring if atrazine is used. If soybeans will be planted the following spring, metribuzin (Dimetric, Glory, Metri, Metribuzin, Tricor, and others) can be used instead of atrazine to enhance the Gramoxone activity. These chemistries are contact herbicides requiring thorough coverage and more spray volume than does a glyphosate treatment.
To improve the chances of getting good control after wheat harvest, apply the postharvest treatments in the morning hours or after the field has received some moisture, not when the kochia plants are under maximum stress. If kochia has been severely drought stressed before treatment, waiting a couple of days following a good rain may provide optimum control from the herbicide treatment. If glyphosate is the product of choice, use the highest labeled rate, and make sure to add ammonium sulfate and any necessary surfactants.