Influence of Herbicides and Timing on Kochia (Kochia scoparia) Control in Spring Wheat (T. aestivum).

In central and western regions of South Dakota, Kochia (Kochia scoparia) is considered one of the most problematic weeds in small grain crops such as spring wheat (T. aestivum). Chemical control is a viable option, however Group 2 (ALS inhibitor) and Group 9 (EPSP synthase inhibitor (glyphosate)) resistant kochia have been documented in South Dakota, reducing herbicide options. Furthermore, kochia resistance to Group 4 (growth regulator) herbicides is a concern in South Dakota as well. The purpose of this study was to evaluate residual and foliar control of herbicides containing multiple active ingredients on kochia. Herbicides consisting of two or more of the following active ingredients were evaluated: Bromoxynil, MCPA ester, Fluroxypyr, Clopyralid, and 2,4-D along with an untreated control. Two application timings were made, an early application before kochia emergence to evaluate residual control, as well as a second timing when kochia was approximately 7 cm tall to evaluate foliar control. Both timings were evaluated for control, as well as photographed at approximately 7, 14, 21, and 28 days after treatment (DAT).  Early application timing provided better control of kochia. Herbicides containing Fluroxypyr provided the most effective foliar and residual control of kochia, and when tank-mixed with 2,4-D offered superior control to MCPA ester. Herbicides containing Clopyralid offered effective residual control. Based upon information obtained from this study, earlier timing of herbicide applications offers improved opportunity to control kochia, while herbicide selection may improve kochia control and reduce the opportunity for herbicide resistance.  Continued research on additional herbicides is necessary to increase crop yields and minimize instances of resistance where kochia is a problem.