Botrytis Cinerea, also called Grey Mold, is a fungus that overwinters on dead tissue from the vineyard floor and on the vine, such as cluster stems or mummified berries. Typically infects diseased tissue first (hail/bird damaged, powdery mildew, etc.) and then after gaining a stronghold, spreads to healthy tissue.
Can impact leaves, shoots and blossom clusters. First seen on leaves as small dark green spots, typically around a vein, that turn into large brown lesions. It can also infect developing blossoms and shoots, but is most commonly associated with a brown spreading cluster rot of ripening berries. Under certain conditions, the rot will form a fluffy grey-brown growth with visible spores.
Botrytis thrives in cool, humid weather. Rainfall is not required for disease development. Moisture caused by fog or dew can trigger the disease with rapid spread at 59° -77°F.
For varieties that are susceptible to Botrytis a spray of Rovral, Vangard, or Elevate is applied at bunch closing, again at veraison and during ripening if the weather is wet. A spray is advisable at bloom only if the variety is highly susceptible to Botrytis rot and the weather is very wet during the bloom period. Leaf pulling and shoot positioning to allow good air movement and spray penetration throughout the canopy is recommended.