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15.  THREE-WAY HERBICIDE MIXTURE INCREASED LEAFY SPURGE CONTROL

Katheryn M. Christianson* and Rodney G. Lym1

Abstract: Herbicide mixtures often provide greater control of perennial weed species than the single components alone. For example, picloram plus 2,4-D provides a 20 to 30% increase in long-term leafy spurge control compared to either herbicide applied alone. Timing of herbicide application also affects herbicide efficacy on leafy spurge. For instance imazapic fall-applied provides 80 to 90% leafy spurge control 1 yr after treatment, but only 20 to 30% control when the same treatment is applied in the spring. The purpose of this research was to evaluate long-term leafy spurge control with herbicide mixtures. The study evaluated leafy spurge control by imazapic applied in the spring (or fall) followed by picloram plus 2,4-D in the fall (or spring), picloram plus 2,4-D applied in the spring (or fall) followed by imazapic in the fall (or spring), and all three herbicides applied tank-mixed together in the spring (or fall). The three herbicide mixture of picloram plus 2,4-D plus imazapic applied once in the spring provided the best long-term control and averaged 98% 24 MAT (months after treatment) compared to less than 60% when the herbicides were applied alone. The same three herbicide treatment applied in the fall only averaged 15% control 24 MAT. The best split treatments were picloram plus 2,4-D applied in the spring followed by imazapic in the fall and imazapic fall-applied followed by picloram plus 2,4-D in the spring. These treatments averaged 85 and 61% control in August of 1999 and 2000, respectively. No grass injury was observed following any of the rotational treatments.
 


1Katheryn M. Christianson* and Rodney G. Lym, Research Specialist and Professor, Plant Sciences Dept., North Dakota State University, Fargo, ND 58105. *Presenter.

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