Management of bitter rot and ripe rot of grapes in sub-tropical vineyards in Australia
Abstract: Two bunch rot diseases associated with viticulture in warm and wet conditions arebitter rot, (Greeneria uvicola) and ripe rot (Colletotrichum acutatum). Surveys of vineyards inthe Hunter Valley region of New South Wales revealed that in some seasons these are thepredominant fungi associated with bunch rots. Our observations also demonstrate that bitter rot isassociated with growing seasons that are warmer and drier than normal while B. cinereapredominates in cooler and wetter years. Mature berries from seven Vitis vinifera cultivars(Cabernet Sauvignon, Chardonnay, Sauvignon Blanc, Semillon, Shiraz, Traminer and Riesling)were evaluated for susceptibility to C. acutatum and G. uvicola infection and all were found to beequally susceptible. Susceptibility in field grown vines is linked to date of maturity and regionalclimatic events (rainfall and temperature). In a series of in vitro screening trials, fungicidesbelonging to the strobilurin group were found to be the most effective at inhibiting myceliagrowth of C. acutatum and G. uvicola. Fungicides registered in Australia and commonly used forB. cinerea management (e.g. chlorothalonil, iprodione and pyrimethanil) were not as effective.As strobilurin fungicides cannot be applied to wine grapes grown in Australia after bunch closurewe examined their efficacy at preventing C. acutatum and G. uvicola flower infections. Inexperiments using potted and field-grown grapevines an application of Cabrio (a.i.pyraclostrobin) at flowering was found to limit C. acutatum and G. uvicola infection. Acombination of canopy management that avoids over exposing fruit to heat stress andstrategically applied strobilurin sprays, coupled with growing varieties that can be harvested priorto the onset of summer rainfall in sub-tropical areas appears to be the best management option forbitter rot and ripe rot of grapes in Australia.