Management of non-Botrytis bunch rots

Abstract

Bunch rot of grapes can be caused by a complex of different organisms depending on vineyard location and characteristics. The relative frequency of organism isolation with phenological growth stage was investigated at a cabernet sauvignon vineyard in the Hastings Valley. The predominant bunch rot pathogens isolated were Colletotrichum acutatum (ripe rot) and Greeneria uvicola (bitter rot). Isolation of Botrytis cinerea was infrequent. Both C. acutatum and G. uvicola infected postveraison berries, immature berries resisted infection. G. uvicola also infected detached vine leaves. Growth of both organisms on PDA and berry infection was favoured by temperatures relatively higher than that encountered for B. cinerea. B. cinerea out-competed both C. acutatum and G. uvicola at 20 ºC but not at 27 ºC. Light exposure, both UVB and white light had no effect on the rate of bunch rot progression. High humidity favoured berry infection and infection was possible at a low relative humidity if the berries were incubated at 100% relative humidity for 24 hours post-inoculation before transfer to a low humidity environment. C. acutatum isolates from grapes were not host specific, and were able to infect blueberries, olives and strawberries. A number of fungicide field-based trials were conducted in the Hunter and Hastings Valley. While none of the treatments tested were completely satisfactory for bunch rot management a number of commercially available products did reduce the incidence and severity of bitter rot and ripe rot at harvest. These products included Shirlan (a.i. Fluazinam) applied as a dormant spray and strobilurins (e.g. Amistar, Cabrio) applied at flowering and late in the season.

Summary

Determined fungicide sensitivity of 50 fungal isolates of Greenaria, Colletotrichum,Botrytis, as well as Penicillium, Aspergillus and Alternaria and determined fungal competition on berry surface.