Control of later-emerging kochia in wheat or wheat stubble
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
While 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. Most kochia are now ALS-resistant.
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. With most of the wheat jointed now, the use of dicamba products is likely no longer an option this season.
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. These two products can be applied at later growth stages of wheat. They are both translocated (Starane more so than Huskie) and are effective on kochia. Huskie should be applied with NIS and ammonium sulfate according to the label.
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. Clarity or Starane tanked mixed with a pound of atrazine and 2 oz of Sharpen have provided excellent control of kochia following harvest. This is another option depending on future cropping plans.
An additional 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. Wheat can be planted 4 months after a metribuzin application. 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 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.
Recent research results
In 2014, a trial at the K-State Southwest Research-Extension Center – Tribune field compared several herbicide products applied at different times for kochia control in an irrigated wheat field. The field was seeded late at the rate of 40 lbs/acre to simulate a relatively thin stand. The only weed present in this field was kochia. The wheat was harvested July 9.
Comments on this trial:
- At the time the pre-joint treatments were applied on April 17, kochia were very small. The largest kochia were about 0.5 inches tall. A significant amount of kochia emerged following this pre-joint treatment. All pre-joint treatments provided excellent control of kochia 9 days following application. A rating 28 days after application on May 25 suggest that kochia were emerging through any dicamba applications, as well as the Clarity+Huskie application. Only those pre-joint treatments that included 2 oz of Zidua provided excellent residual control of kochia. Zidua has limited foliar activity and primarily controls later-germinating seedlings. The kochia that were present following wheat harvest after the pre-joint treatments containing Zidua (treatments 2 and 3) were much smaller and emerged later than kochia in the other pre-joint treatments. However, it is also important to note that Zidua is only labelled up to the 4 tiller stage of wheat, which often occurs prior to mid-April in most wheat fields.
- On May 14, the WideMatch treatment was applied to kochia 0.5 to 1.5 inches tall. WideMatch did a very good job controlling the kochia, indicating that coverage was adequate. Complete control was not attained, however. The postharvest treatment following WideMatch applied at flag leaf did provide complete control of kochia. At the time the postharvest treatments were made, the kochia following the WideMatch treatment made at flag leaf were much smaller than the kochia following the earlier, pre-joint treatments.
- The wheat was harvested July 9. At the time of the postharvest treatments, July 14, kochia was actively growing and protruding above the stubble. Much of the kochia was 15-20 inches tall at that time. Where there was excellent in-crop control, only a few kochia were present and those plants were about 2-6 inches tall.
- The heavy density of kochia in the stubble following the pre-joint Clarity+2,4-D treatment proved to be unmanageable after harvest. The postharvest treatment of Clarity+2,4-D provided 64% control, which would be considered a failure.
- Huskie+Clarity (treatment 4) provided about 75% control of kochia at the end of the season. A postharvest treatment of atrazine and Sharpen provided very good control, with only an occasional plant recovering.
- The incrop treatment with Rave (treatment 5) did not provide adequate control in the wheat crop, likely because the kochia in this trial were ALS-resistant and the dicamba residual control was too short. The postharvest treatment of atrazine+Sharpen did provide very good control, however (as it did following the incrop Huskie treatment).
- A postharvest only approach isn’t recommended. Unfortunately, many producers attempt to manage kochia in this manner, especially when the wheat crop is marginal.
- The best of the postharvest-only treatments was Sharpen+atrazine+Clarity, which was the only treatment to exceed 90% control by August 13. Postharvest-only treatments that provided inadequate control were Clarity+atrazine and Clarity+2,4-D, with less than 70% control.
Dallas Peterson, Weed Management Specialist
Curtis Thompson, Extension Agronomy State Leader and Weed Management Specialist