Powdery Mildew on bunch stalks - ID Photos
Above: Late season Powdery Mildew can flare up and infect bunch the racchi and any 'green' unset berries. This type of infection is not considered to affect wine quality as the fruit (the berry) is immune from Powdery and does not have any Powdery on its surface.
Careful harvesting may be necessary. Machine harvesting will remove the fruit and leave behind the infected racchi. Care needs to be taken, it is best not to pick very hard when you see infected racchi, so as to not contaminate the grape load by shaking them off as well as the fruit.