Suppression of Frankliniella bispinosa (Thysanoptera: Thripidae) and the fungal pathogen Colletotrichum gloeosporioides, with pesticides during the bloom cycle and improved fruit set on 'Navel' orange in Florida

Four field experiments were conducted in two 'Navel' orange groves in southwest Florida between 1988-1990. Insecticides were applied alone, in combination with the fungicide benomyl, or benomyl was applied alone during 'Navel' orange flowering cycles between February and April. The duration and intensity of flowering differed each year. Population densities and peak activity of Frankliniella bispinosa (Morgan) differed by year and by site during the same year. Fifty-unit samples of small (5-9 mm), medium (10-13 mm), and large (greater than or equal 14 mm) floral buds, open flowers, and fruitlets were evaluated to determine the optimal stage of floral development for sampling adults and larvae of F. bispinosa. All floral stages were infested but open flowers consistently had the highest numbers of both adults and larvae and were used to assess treatment differences in thrips populations after 1988. Results showed a positive relationship between population suppression of F. bispinosa during the flowering cycle and subsequent 'Navel' orange fruit set in late june or early July. Chlorpyrifos, dimethoate, and formetanate hydrochloride were effective in suppressing numbers of F. bispinosa, with activity lasting 3-7 d after application. Two or more applications of benomyl resulted in fruit set increases each year in the four field experiments compared with fruit set increases in three of four experiments where insecticides only were applied. The fungal pathogen, Colletotrichum gloeosporioides Penzig, was identified previously as the causative organism for postbloom fruit drop disease on citrus. This study demonstrated that there are two potential factors (F. bispinosa arid C. gloeosporioides) involved in reduced fruit set on 'Navel' orange during the flowering cycle in Florida.