Assessing and managing disease affected fruit in the vineyard: the Australian experience

The unusually wet season across south-eastern Australia in 2010–2011 saw grapegrowers exhausted after endless hours of spraying, often in vain, to control the dreaded trifecta of downy mildew, powdery mildew and botrytis bunch rot (botrytis). Mildew infection during flowering and fruit set damaged grape berries providing infection sites for the opportunistic ‘wound’ fungi that cause bunch rot. However, the interaction between the diseases was not always detrimental. There were reports that defoliation caused by downy mildew increased air circulation in the canopy which, in turn, reduced the severity of bunch rot. Nevertheless, the pressure on vineyard managers to act in controlling these diseases was relentless, even when certain actions, with hindsight, proved fruitless. Liz Riley, a viticulturist and consultant in the Hunter Valley, coined the term ‘koalas’ to denote grape bunches with large areas of ‘grey and fuzzy’ mould (Figure 1). The case for crop rejection can be all too clear when there are numerous ‘koalas’ and nearly every bunch is rotten to some degree.