Impact of Clopyralid on Strawberry (Fragaria x ananassa, 'Festival') Growth and Yield

Clopyralid is the only post emergent broadleaf herbicide registered for use in strawberry (Fragaria square ananassa) in Florida. An experiment was conducted in 2013 to evaluate the impact of clopyralid rate (0, 140, 280, and 560 g center dot ha(-1)) and application timing (10 and 19 December and 2, 16, and 30 January) on strawberry vegetative and reproductive growth. Two and four weeks after spraying there was a significant rate by application timing interaction (P = 0.0004 and 0.0013) on leaf number. Clopyralid applications on 10 and 19 December had no impact on leaf number whereas there was a 40% and 52% reduction in leaf number, respectively, compared to the untreated control if sprayed at 280 or 560 g center dot ha(-1) on 2 January. Similar trends were observed when clopyralid was sprayed on 16 January. There was a significant interaction (P = 0.0227) between herbicide rate and application timing on berry yield. Lower yields were obtained at the highest herbicide rate compared to the untreated control when applied on 10 December. Clopyralid applications later in the season did not impact yield. We conclude that clopyralid applied at label rates may reduce leaf number but is unlikely to impact yield of strawberry.