Anthracnose is caused by the fungus Elsinoe ampelina, which reduces the quality and quantity of fruit and weakens the vine. It is a significantly found in rainy, humid, warm grape growing regions. It thrives on conditions similar to Black Rot, so the two disease are often present together.
Shoots, berries and leaves can all have symptoms, but the sunken spots with dark margins on the shoots, are the easiest to spot. Young growth is most susceptible and the disease can kill growing shoots by girdling off the tips. Leaf spots are whitish/grey with dark margins and can develop into holes creating a “shot-hole” effect. Berries develop purple spots that turn grey with dark margins and then often crack and decay.
The fungus overwinters on infected canes and berries and releases spores (conidia) when the temperature exceeds 36 degrees and leaves are wet for 24 hours or more. The spores germinate at temperatures between 36-90. Higher temperatures cause a much more rapid spread of the disease (symptoms appear in 13 days after infection at 36 degrees, but only take 4 days at 90 degrees). Rapid infection can occur with heavy rainfall and warm temperatures.
A dormant spray of lime sulfur, just prior to bud break, will help clean-up remnants of Anthracnose from the previous season. In addition, preventive fungicide sprays at 2-week intervals from bud break until the fruit begin to turn color. Prune out damaged shoots and clusters and remove the debris from the vineyard. Also, rake the rows after harvest to remove fallen berries.