Impact of Application Time and Clopyralid Rate on Strawberry Growth and Yield

Abstract

Hard-seeded, broadleaf, winter annual weeds in strawberry plasticulture production in Florida emerge in the crop holes in the plastic mulch and reduce berry yield and quality. Clopyralid is registered for POST control of broadleaf weeds, but herbicide damage has been observed in commercial fields, and preliminary observations suggest that effects vary with time of application. To address this issue, an experiment was conducted in 2012 to 2013 and 2013 to 2014 to evaluate clopyralid rate (0, 140, 280, and 560 g ae ha−1) and application time on strawberry vegetative and reproductive growth. Clopyralid applications at 280 and 560 g ae ha−1on January 2 and 16, 2013 (yr 1) reduced leaf number per plant by 33 to 44% and increased the number of deformed leaves per plant compared with the nontreated control. This pattern was not observed in yr 2. In yr 1 and 2, two times the label rate of clopyralid (560 g ae ha−1) tended to reduce the total number of floral buds compared with the nontreated control by 12 to 17%. None of the herbicide rates or application times reduced the number of flowers per plant, marketable berries per plant, yield over time, or total yield. We conclude that clopyralid applications at the rates and application times tested in this study may cause leaf damage and may reduce leaf number in some situations but does not affect yield.