THE EFFECT OF FUNGICIDE ON THE GROWTH OF APPLE BITTER ROT PATHOGENS

Abstract

Bitter rot, an economically important disease of apples in the southeastern U.S., is caused by a complex of plant pathogenic fungi. Fruit infection can result in large yield losses. Control of this disease is contingent upon the effectiveness of several commonly used fungicides. Two fungal species, Colletotrichum gloeosporioides (C.g.) and C. acutatum (C.a.), cause bitter rot. Isolates of both species also show a large degree of genotypic variation. The objective of this study was to determine the effect of several fungicides: benomyl (Benlate), Captan, Mancozeb (a combination of zinc ion and manganese ethylene bisdithiocarbamate, Dithane), and zinc dimethyldithiocarbamate (Ziram). Four concentrations (0, 0.5, 1, and 2 ppm) of each fungicide were used. Fungal growth was quantified by measuring colony diameters 3 and 6 days after incubation. Among the fungicides tested, only Benlate and Ziram significantly reduced fungal growth. Average growth reductions of C. gloeosporioides with Benlate and Ziram were 87% and 29%, respectively. In contrast, average growth reductions of C.a. with Benlate and Ziram were 60% and 52%, respectively. In conclusion, Benlate was the most effective fungicide in reducing overall fungal growth, while Ziram was more effective in reducing the growth of C.a.