Managing the threat of botrytis over summer
Flowering occurs from late October to late December, depending on variety and location, and it is arguably the most important time to protect and maintain vine health. For most export winegrapes, the key botryticides Scala® and Teldor® must be applied at no later than 80% capfall which coincides with the risk period for latent botrytis infection. Switch, which contains an active with the same mode of action group as Scala (Group 9), may be used until berries are 4 mm in diameter. Canopy management, crop load, nutrition and irrigation can be used to reduce the risk of botrytis developing following wet conditions after veraison. Fortunately, once veraison occurs, the risk of new downy and powdery mildew infections is minimal (apart from new, unprotected leaf growth).
As daytime temperatures increase in the summer months, increased care should be taken when spraying with translaminar or systemic fungicides to enable droplets to survive long enough to be taken into the leaf or bunch. Similarly, some protectant fungicides can damage the crop if used during periods of high temperature or humidity.
BOTRYTIS DISEASE CYCLE
Overwintering as resting bodies (sclerotia) on the vine, vineyard floor and other plants..
High soil moisture triggers the release of spores, which are then spread to flowers by the wind.
Infections become visible and spread rapidly, rotting entire bunches.
Sclerotia form on debris and overwinter.