Evaluating the degree day model for timing insecticide applications to suppress the bermudagrass stem maggot

Abstract

The bermudagrass stem maggot (BSM; Atherigona reversura Villeneuve) can severely damage bermudagrass [Cynodon dactylon (L.) Pers.] forage. Strategically timed pyrethroid applications significantly reduce BSM populations, but application timing needs to be further refined. Therefore, this study evaluated the use of a degree day model for timing insecticide applications to suppress the BSM. The research was conducted in a split plot design with two bermudagrass cultivars (‘Alicia’ and ‘Tifton 85’) and eight insecticide timing treatments ranging from 100 to 400 growing degree days (GDDs) plus an untreated control. The use of insecticide increased mean herbage accumulation and plant height more than the untreated control, but the timing of the insecticide applications did not affect either response (P < 0.01). All insecticide-treated plots had less BSM damage than the untreated control (P < 0.01). The canopies treated with insecticide at 100 and 200 GDD had a cooler micro-environment than those treated at 150 GDD, but all other insecticide timing treatments were not different from those treatments (P < 0.01). Tifton 85 accumulated more herbage, resulted in a taller canopy, and sustained less damage by the BSM than Alicia (P < 0.01). Canopy temperature did not differ between cultivars (P = 0.94). It was hypothesized that greater losses would have occurred in the earliest and latest insecticide treated plots based on feedback from area bermudagrass growers. However, it appears that day of application may be confounded with time of application in these reports. Future investigations should explore this interaction to further refine application timing.