Investigations of the sensitivity of ornamental, fruit, and nut plant species to driftable rates of 2,4-D and dicamba

An experiment was conducted in 2017 and 2018 to determine the sensitivity of driftable rates of 2,4-D and dicamba with or without glyphosate on common ornamental, fruit, and nut species. Three driftable rates corresponding to 1/2, 1/20th, and 1/200th of the manufacturer's labeled rate (1 x rate) of 2,4-D (1.09 kg ae ha(-1)), 2,4-D plus glyphosate (1.09 kg ae ha(-1) plus 1.10 kg ae ha(-1)), dicamba (0.56 kg ae ha(-1)), and dicamba plus glyphosate (0.56 kg ae ha(-1) plus L10 kg ae h(-1)) were applied to apple, crabapple, dogwood, American elderberry, American elm, grapevine, hydrangea, red maple, pin oak, peach, pecan, eastern redbud, rose, red raspberry, strawberry, sweetgum, nannyberry viburnum, and black walnut plants. Visible estimates of injury were recorded 28 and 56 days after treatment (DAT). Plant measurements included leaf malformation, tree trunk growth, and shoot length. Across all species, the 1/2 x rate of 2,4-D plus glyphosate resulted in 61% injury 28 DAT, whereas the' x rate of dicamba plus glyphosate resulted in 51% injury. Across plant species and herbicides, 1/2 x, 1/20 x, and 1/200 x rates caused injury ranging from 3% to 100%, 0% to 66%, and 0% to 19%, respectively. Hydrangea was the least sensitive species; grapevine was most sensitive. Changes in plant measurements were dependent on the species and herbicide applied. Treatments at the 1/2 x or 1/20 x rate resulted in shoot length, leaf malformation, and trunk tree diameter differences for 11, 10, and 7 species, respectively, compared with nontreated plants. Collectively, the measurements and visual injury assessments indicated apple, red maple, peach, and pin oak were more sensitive to treatments containing dicamba, whereas black walnut, grapevine, and American elm were more sensitive to 2,4-D. Although the 1/200 x rates of 2,4-D and dicamba did not result in changes to plant measurements, obvious injury symptoms were observed, which could render these plants unsalable.