Response of Wine Grape Cultivars to Simulated Drift Rates of 2,4-D, Dicamba, and Glyphosate, and 2,4-D or Dicamba Plus Glyphosate

Abstract

Greenhouse experiments were conducted at Wooster, OH, during 2010 and 2011 growing seasons to evaluate the responses of five wine grape cultivars to sublethal doses of 2,4-D, dicamba, and glyphosate, and the ‘Riesling’ grape to mixtures of 2,4-D plus glyphosate and dicamba plus glyphosate. Treatments were made using a spray system calibrated to deliver 0.757 L min−1at 276 kPa and 4.8 km h−1. Herbicides were delivered through 8002 flat spray nozzles and applied at 1/30, 1/100, and 1/300 of the recommended field rate of 840, 560, and 840 g ae ha−1for 2,4-D, dicamba, and glyphosate, respectively. Injury was observed in all treatments 7 d after treatment (DAT). However, injury symptoms greater than 10% were observed 42 DAT in plants treated with 2,4-D at all rates and plants treated with dicamba at the two highest rates. Injury (35%) at 357 DAT was noted only in plants treated with the highest rate of 2,4-D. French hybrids showed slightly less injury symptoms compared with wine grapes at 7 and 42 DAT. Shoot length reduction in plants treated with 2,4-D at the highest rate was 43, 84, and 16% at 7, 42, and 357 DAT, respectively. Glyphosate caused the fewest injury symptoms in Riesling compared with 2,4-D and dicamba when applied separately or tank mixed with glyphosate. Shoot length reduction in Riesling was observed 42 DAT with all rates of 2,4-D, with and without glyphosate and dicamba, and dicamba plus glyphosate at the highest rate; however, at 357 DAT, no effect was observed in shoot length. Spray drift of 2,4-D and dicamba can severely injure grapes, with injury increasing with increased exposure. The combination of 2,4-D plus glyphosate caused greater injury and shoot length reduction in grapes than glyphosate applied alone.