Dicamba Weed Size Evaluation.

Weed herbicide tolerance and resistance is intensifying rapidly in current crop production systems. Farmers result in applying multiple applications to their fields to effectively control weeds. However, this adds a tremendous expensive to the farmer and also adds more pesticides to the environment. Herbicides vary in the way they control weeds through their sites of action as well as their modes of action. Applying more than one herbicide that consists of multiple modes of action can slow down weed resistance and limit selection pressure by adding diversity in the mix. Dicamba (3,6-dichloro-2-methoxybenzoic acid) is a benzoic acid herbicide that controls broadleaf weeds. Recently, Monsanto and Dow AgroSciences have made it possible to apply dicamba to soybeans by developing Dicamba resistant soybeans (Purdue Extension, 2012). Dicamba resistant soybeans add an additional method of broadleaf weed control and help to preserve current herbicide program strategies. This experiment evaluates the importance of timely herbicide applications to achieve effective broadleaf weed control in Dicamba resistant soybeans. A preemergance application will be made 14 days prior to planting. Postemergence applications will be made at weeds less than 2 inches, 4-6 inches, and 8-10 inches. Assessments will be made 3, 7, 14, and 21 days after treatment to evaluate broadleaf and grass weeds for control individually based on a percentage scale (0-100%; where 0 = no control and 100 = complete kill). Overall crop injury will also be evaluated using the same scale as the weed control. The results of the experiment demonstrated that weeds should be sprayed at 2 inches or less to limit the amount of weed escapes and provide more effective weed control.