"The recent registrations of dicamba- and 2,4-D-resistant soybeans will likely increase the amounts of dicamba and 2,4-D used in Michigan. Off-target movement to sensitive crops, such as dry bean, will be of greater concern with increased use. In 2017 and 2018, field experiments were conducted at two locations in Michigan to examine the effects of low rates of dicamba and 2,4-D on dry bean. In the first experiment, three rates of dicamba and 2,4-D were applied to V2 and V8 black and navy beans. Dicamba and 2,4-D rates that caused 20% injury to dry beans 14 DAT were 4.5 and 107.5 g ae ha-1 , respectively. Delays to 50% maturity ranged between 8-16 d for 56 g ae ha-1 of dicamba, and 2-9 d for 112 g ae ha-1 of 2,4-D. Over four site-years, the rate of dicamba that caused a 10% reduction in yield was 9.8 g ae ha-1, which was 1.7% of the field use rate. 2,4-D rates up to 112 g ae ha-1 did not reduce dry bean yield. The second experiment examined the effects of the interaction between low rates of dicamba (5.6 g ae ha-1) or 2,4-D (11.2 g ae ha -1) alone and with glyphosate (8.4 g ae ha-1) as tank-contaminants with dry bean herbicides. Results indicated that when dicamba tank-contaminations occurred with a dry bean herbicide there was a synergistic effect. Over two site-years, dry bean yields were between 6-10% lower when dry bean herbicide was applied with dicamba or dicamba plus glyphosate, compared to dicamba and dicamba plus glyphosate alone. Tank-contamination of 2,4-D (11.2 g ae ha -1) had little effect on dry bean with or without dry bean herbicides. This work further stresses the need for caution when using dicamba or 2,4-D herbicides near sensitive crops."--Page ii.
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