vinegrowing

Chemical management methods

Pesticides used to control downy mildew fall into two categories;

  • pre-infection - preventative, and
  • post-infection - curative

Preventative sprays are applied just prior to a predicted infection period with spray programs commencing when shoot length are about 10cm. These sprays help reduce the chance of zoospores germinating.

Cultural management methods

Site selection

Well drained sites with day long sun exposure and good air circulation are less prone to downy mildew.

Varietal sensitivity

Varieties with thick leaves and large juice berries are more susceptible than those with thin or hairy leaves.

Canopy management

Practices that promote open canopies with high levels of light penetration and air circulation reduces humidity in the canopy and promote more rapid drying after a rain event and better spray penetration.

Monitoring

Effective management of downy mildew starts with careful monitoring of the vineyard looking for infections triggered by favourable weather conditions. Collaboration between local growers will increase the chance of spotting primary outbreaks and enable coordinated management programmes.

Monitoring every 7 - 10 days when weather conditions are favourable at 2 - 3 weeks after budburst or at 10cm shoot length.

Epidemiology

Oospores – sexual structure, resting bodies that form in late summer and overwinter in fallen leaves and prunings.Resistant to fungicide and harsh weather. May also overwinter as mycelium in buds.Oospores germinate in favourable conditions to release Zoospores.

Symptoms on other parts of the vine

Infection on shoots appears as shiny brown patches which spread to leaf stalks causing necrosis and leaf fall. After suitable warm humid nights sporulation will occur to coveraffected parts with white down. Affected young shoots may thicken and distort.

Symptoms on the leaves

(1) In Spring – Primary infection results in the appearance of yellow oil spots about 10mm in size. These grow to about 50mm and merge to cover the leaf. With age they become necrotic developing a brown halo.

Botrytis: Biology, Pathology and Control

Botrytis cinerea and other Botrytis species are important pathogens of nursery plants, vegetables, ornamental, field and orchard crops and stored and transported agricultural products.

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