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.
Highlights
Herbicide resistance threatens farm sustainability, with more than 150 unique cases confirmed in the United States to date (CAST 2012; Evans et al 2015; Heap 2019; Menalled et al 2016; Rubin 2015; Yu and Powles 2014)
Cucumbers treated with dicamba at the 1/75 rate (22% injury) had higher injury levels than cucumbers treated with the same relative rate of 2,4-D (15% injury) when averaged over application timings. This trend remained true for the 1/250 rates, with dicamba causing greater visual injury than 2,4-D (10% and 6%, respectively)
With respect to the rate and application timing interaction, the 1/75 rates resulted in a higher level of injury than the 1/250 rates when averaged over herbicide applied (Table 1)
Summary
Herbicide resistance threatens farm sustainability, with more than 150 unique cases confirmed in the United States to date (CAST 2012; Evans et al 2015; Heap 2019; Menalled et al 2016; Rubin 2015; Yu and Powles 2014). Resistance to acetolactate synthase inhibitors, acetyl coenzyme-A carboxylase inhibitors, and triazines are prevalent, glyphosate resistant weeds are the primary management concern in many major agronomic crops, including corn (Zea mays L.), soybean [Glycine max (L.) Merr.], and cotton (Gossypium hirsutum L.) (Riar et al 2013; Schuster and Smeda 2007; Sosnoskie and Culpepper 2014). To combat glyphosate-resistant weeds, some crop cultivars have been genetically engineered with additional resistance to 2,4-D or dicamba (Behrens et al 2007; Gressel et al 2017). Weed management programs using 2,4-D and dicamba have proven effective against some of the most problematic broadleaf weeds in the United States, including Palmer amaranth Sauer] (Meyer et al 2015), horseweed (Conyza canadensis L.) (Kruger et al 2010), and giant ragweed (Ambrosia trifida L.) (Barnett et al 2013)
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