Strawberry is an important horticultural crop in Florida. The long growing season and escapes from fumigation and PRE herbicides necessitate POST weed management to maximize harvest potential and efficiency. Alternatives to hand-weeding are desirable, but clopyralid is the only broadleaf herbicide registered for use. Weed control may be improved by early-season clopyralid applications, but at risk of high temperature and increased strawberry injury. The effect of temperature on clopyralid safety on strawberry is unknown. We undertook a growth chamber experiment using a completely randomized design to determine crop safety under various temperature conditions across acclimation, herbicide application, and post-application periods. There was no effect of clopyralid on the number of strawberry leaves across all temperatures. Damage to the strawberry manifested as leaf malformations. Acclimation temperatures affected clopyralid-associated injury (p=0.0309), with increased leaf malformations at higher temperatures (27 C) compared to lower (18 C) temperatures. Pre-treatment temperatures did not affect clopyralid injury. Post-application temperature also affected clopyralid injury (p=0.0161), with increased leaf malformations at higher temperatures compared to lower ones. Clopyralid application did not reduce flowering or biomass production in the growth chamber. If leaf malformations are to be avoided, consideration to growing conditions prior to application is advisable, especially if applying clopyralid early in the season.

Common groundsel is an important weed of strawberry and other horticultural crops. Few herbicides are registered for common groundsel control in such crops, and understanding and predicting the timing and extent of common groundsel emergence might facilitate its management. We developed simple emergence models on the basis of soil thermal time and soil hydrothermal time and validate them with the use of field-derived data from Minnesota and Ohio. Soil thermal time did not predict the timing and extent of seedling emergence as well as hydrothermal time. Soil hydrothermal time, adjusted for shading effects caused by straw mulch in strawberry, greatly improved the accuracy of seedling emergence predictions. Although common groundsel generally emerges from sites at or near the soil surface, the hydrothermal model better predicts emergence when using hydrothermal time at 5 cm rather than 0.005 cm, probably because of the volatility of soil temperature and water potential near the soil surface.

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−1 on 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.