Aetiology, effect of chemicals, and influence of fruit exudates, insects and fruit maturity on the incidence of fruit speckle of banana

Abstract

The symptoms of fruit speckle of banana are minute reddish-brown to black spots (0.5–1 mm in diameter) often with an oil-soaked or water-soaked margin. Research was conducted into the aetiology, aspects of epidemiology and chemical control of fruit speckle. In a field planting of Lady-finger banana, bunches injected at bunch emergence with the fungicide azoxystrobin (0.15 g a.i./L) and sprayed fortnightly with azoxystrobin (0.25 g a.i./L) significantly reduced the number of speckle lesions/cm compared with bunches injected and sprayed fortnightly with insecticides indicating fruit speckle was caused by fungi. Of the 11 species of fungi recovered from speckle lesions, only Colletotrichum musae, Fusarium oxysporum and F. semitectum reproduced speckle-like symptoms on young fruit. Studies on fruit speckle epidemiology showed spraying young fruit with a 10% sap solution before inoculation with Fusarium spp. caused a 3-fold increase in the number of speckle lesions but had much less of an effect on the incidence of speckle following inoculation with C. musae. Fruit was also shown to be less susceptible to fruit speckle as it matured. The presence of flower thrips had little effect on the incidence of speckle on fruit inoculated with C. musae but caused a 10-fold increase in the incidence of speckle on fruit inoculated with Fusarium spp. In an in vitro experiment, the fungicides propineb, azoxystrobin, trifloxystrobin, copper oxide, mancozeb and chlorothalonil effectively reduced the disease compared with the inoculated control.