Sweetpotato response to reduced rates of dicamba

Abstract

AbstractA field study was conducted in Mississippi to determine the effect of reduced dicamba rates on sweetpotato crop tolerance and storage root yield, simulating off-target movement or sprayer tank contamination. Treatments included a nontreated control and four rates of dicamba [70 g ae ha−1 (1/8×), 35 g ae ha−1 (1/16×), 8.65 g ae ha−1 (1/64×), and 1.09 g ae ha−1 (1/512×)] applied either 3 d before transplanting (DBP) or 1, 3, 5, or 7 wk after transplanting (WAP). An additional treatment consisted of 560 g ae ha−1 (1×) dicamba applied 3 DBP. Crop injury ratings were taken 1, 2, 3, and 4 wk after treatment (WAT). Across application timings, predicted sweetpotato plant injury 1, 2, 3, and 4 WAT increased from 3T to 22%, 3% to 32%, 2% to 58%, and 1% to 64% as dicamba rate increased from 0 to 70 g ha−1 (1/8×), respectively. As dicamba rate increased from 1/512× to 1/8×, predicted No. 1 yield decreased from 127% to 55%, 103% to 69%, 124% to 31%, and 124% to 41% of the nontreated control for applications made 1, 3, 5, and 7 WAP, respectively. Similarly, as dicamba rate increased from 1/512× to 1/8×, predicted marketable yield decreased from 123% to 57%, 107% to 77%, 121% to 44%, and 110% to 53% of the nontreated control for applications made 1, 3, 5, and 7 WAP, respectively. Dicamba residue (5.3 to 14.3 parts per billion) was detected in roots treated with 1/16× or 1/8× dicamba applied 5 or 7 WAP and 1/64× dicamba applied 7 WAP with the highest residue detected in roots harvested from sweetpotato plants treated at 7 WAP. Collectively, care should be taken to avoid sweetpotato exposure to dicamba especially at 1/8× and 1/16× rates during the growing season.