Aminocyclopyrachlor (AMCP) is a herbicide with an auxin-mimic mode of action. AMCP is registered for use in the United States on right-of-way and other noncropland sites, causing concern for potential off-target spray drift. The objectives of this study were to evaluate cantaloupe and eggplant response to simulated AMCP spray drift in the field and cotton response in the greenhouse. Cantaloupe and eggplant responded with little to no injury from drift rates up to 10 g AMCP ha−1, roughly 3.2% of the maximum labeled use rate for right-of-way weed control. Slight yield reductions occurred but were not consistent between 2008 and 2009. Therefore, eggplant and cantaloupe injury and yield-reduction potential from AMCP spray drift is low. Cotton response to AMCP drift was compared to similar spray drift rates of 2,4-D and aminopyralid. Cotton responded with injury and reductions in height and dry mass from all three herbicides. Responses were greatest from AMCP, indicating AMCP is potentially more damaging to cotton than 2,4-D or aminopyralid if spray drift occurs, when comparing percentages of labeled rates.
