Off-Target Injury to Southern Landscape Species Following Aminocyclopyrachlor Applications
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Aminocyclopyrachlor is an herbicide for broadleaf weed control that has recently come under scrutiny following reports of injury to landscape ornamentals across the upper Midwestern United States. This herbicide has been shown to provide excellent weed control in warm-season turfgrasses at much lower use rates than that used for cool-season turf, but data are lacking concerning its safety to landscape ornamentals in southern U.S. regions. Parallel studies were conducted in Dallas and Huntsville, TX, locations to evaluate off-target injury effects on sixteen ornamentals and trees commonly used in southern landscapes. In March 2012, just prior to the spring growth flush, aminocyclopyrachlor was applied to potted plants at 0, 0.5, 1, 2, or 4 rates as either as granular [0, 14, 28, 56, or 112 g aiha1 (0.013, 0.03, 0.05, and 0.10 lbs aiA1)] or liquid [0, 11.2, 22.4, 44.8, or 89.6 g aiha1 (0.01, 0.02, 0.04, 0.08 lbs aiA1)] formulations. For the next 8 weeks, plants were evaluated for injury to new growth. Injury was observed in 9 of the 16 species used, but was generally mild to moderate in nature. Species exhibiting the greatest sensitivity to aminocyclopyrachlor included loblolly pine (Pinus taeda), viburnum (Viburnum odoratissimum), nandina (Nandina domestica Compacta), and camellia (Camellia japonica). Extent of injury was not different between granular or liquid formulations, but was less severe at the Dallas location. Results of the study indicate sensitivity within some southern landscape ornamentals to aminocyclopyrachlor.
