Effects of low-dose applications of 2,4-D and dicamba on cucumber and cantaloupe

Abstract

AbstractAgronomic crops engineered with resistance to 2,4-D or dicamba have been commercialized and widely adopted throughout the United States. Because of this, increased use of these herbicides in time and space has increased damage to sensitive crops. From 2014 to 2016, cucumber and cantaloupe studies were conducted in Tifton, GA, to demonstrate how auxinic herbicides (namely, 2,4-D or dicamba), herbicide rate (1/75 or 1/250 field use), and application timing (26, 16, and 7 d before harvest [DBH] of cucumber; 54, 31, and 18 DBH of cantaloupe) influenced crop injury, growth, yield, and herbicide residue accumulation in marketable fruit. Greater visual injury, reductions in vine growth, and yield loss were observed at higher rates when herbicides were applied during early-season vegetative growth compared with late-season with fruit development. Dicamba was more injurious in cucumber, whereas cantaloupe responded similarly to both herbicides. For cucumber, total fruit number and relative weights were reduced (16% to 19%) when either herbicide was applied at the 1/75 rate 26 DBH. Cantaloupe fruit weight was also reduced 21% and 10% when either herbicide was applied at the 1/75 rate 54 or 31 DBH, respectively. Residue analysis noted applications made closer to harvest were more likely to be detectable in fruit than earlier applications. In cucumber, dicamba was detected at both rates when applied 7 DBH, whereas in cantaloupe, it was detected at both rates when applied 18 or 31 DBH in 2016 and at the 1/75 rate applied 18 or 31 DBH in 2014. Detectable amounts of 2,4-D were not observed in cucumber but were detected in cantaloupe when applied at either rate 18 or 31 DBH. Although early-season injury will more likely reduce cucumber or cantaloupe yields, the quantity of herbicide residue detected will be most influenced by the time interval between the off-target incident and sampling.