If fully developed bunches are attacked, they will fail to ripen properly, and the fungus will inevitably end up in the wine, where it creates off flavours. This mildew is one of the few fungal diseases which thrives in hot, dry climates like ours. Organic controls include some common sense gardening. Bright sunlight and good air circulation prevent the spores from spreading, so canopy management is important. If the vine vigour is too high, and there is too much foliage, air stops moving, and shade pockets provide a favorable environment for the fungus.
Most conventional growers use either sulphur or a synthetic equivalent to deal with powdery mildew.
Botrytis is sometimes called bunch rot because it usually affects grapes rather than vines. Whether you have Noble Rot or Sour Rot in your vineyard will depend on the maturity of the fruit and the weather conditions at the time it strikes. Sour Rot will occur when the organism affects unripe or damaged fruit, or when wet conditions close to harvest help it thrive. The fungus will enter through an already existing break in the berry's skin, or it will perforate the skin to make its own entry. Thin skinned varieties with tightly compact bunches like S millon, Sauvignon Blanc, Optima and Chenin Blanc are particularly susceptible.