Carolina geranium ( Geranium carolinianum ) emergence modeling in Florida strawberry fields

Abstract

Carolina geranium ( Geranium carolinianum L.) infestation is a concern for Florida strawberry [ Fragaria × ananassa (Weston) Duchesne ex Rozier (pro sp.) [ chiloensis × virginiana ]] producers. Current control measures rely on hand weeding or clopyralid applications when the weed is small. Unfortunately, early detection tends not to occur due to occlusion by the canopy. Coordinating postemergence control with emergence timing could improve control. Therefore, the objective of this study was to model the cumulative emergence of G. carolinianum in the row middles and transplant holes on the plastic-mulched beds of Florida strawberry fields using accumulated growing degree days (GDD) (thermal or hydrothermal time) as a predictive variable. A 7-yr study was conducted in two strawberry fields within Hillsborough County, FL, for row middles and a 2-yr study was conducted for bed tops. Emergence was modeled as a function of accumulated standard and restricted GDD. The model was calibrated using 5 randomly selected site-years of data and validated with 2 additional site-years for row middles, while only calibration was done for bed tops. Annual variation in emergence timing was driven by both temperature and moisture in the row middles, whereas emergence on the bed tops was influenced by temperature alone. Incorporating restrictions on GDD accumulation reduced overestimation of GDD and improved model prediction (standard GDD model with adjusted R ² = −0.10, RMSE = 37.31; restricted GDD model with adjusted R ² = 0.90, RMSE = 11.46) and enhanced the model’s applicability for row middles over space and time. In contrast, no improvement in model performance was observed for the bed tops. Emergence began simultaneously, but 50% and 90% cumulative emergence occurred at least a week later on bed tops compared with row middles. Overall, G. carolinianum primarily emerged from mid-October to mid-December, which allows implementation of control measures before harvest initiation.