Concern exists among specialty crop producers and processors related to the potential introduction of agronomic crops tolerant of synthetic auxin type herbicides. While anecdotal observations of synthetic auxin herbicide drift on specialty crops have been reported, quantitative data on injury and crop yield is often lacking. The objective of this study was to determine the effect of simulated synthetic auxin drift on potatoes and snap (green) beans. In potatoes, simulated dicamba drift was evaluated at three rates (1.4, 4.2 and 7.0 g ae/ha) and two timings. In snap beans, 2,4-D and dicamba were evaluated individually at the same rates described above but at one application timing. When dicamba was applied to 25 cm tall potatoes, visual injury 10, 24 and 30 days after treatment (DAT) increased with application rate, but by 38 DAT injury was greater than in the non-treated control only at the highest application rate. Potato tuber size distribution was variable and total yield did not differ among treatments and the non-treated control. In snap beans, injury from dicamba 7 DAT ranged from 19% at the low application rate to 45% at the high application rate. By 18 DAT, injury from 2,4-D was similar to the non-treated control. However, early-season injury delayed snap bean flowering and reduced crop yield compared to the non-treated control for all treatments except where the lowest rate of 2,4-D was applied. Snap bean injury from dicamba was greater than that from 2,4-D at all visual rating timings and crop yield was reduced compared to where 2,4-D was applied and the non-treated control.
Soil Science Extension
University of Wisconsin Madison