It is estimated that approximately 175,000 hectares of land are under grapes in Australia for wine, drying and table grapes, making it one of the country’s largest horticultural sectors.
Australian grapes can be affected by a number of diseases, viruses, bacteria and pests that may either destroy or dramatically reduce crop yield and quality. These include downy mildew, powdery mildew, botrytis, phomopsis, black spot, eutypa, lightbrown apple moth, mites, phylloxera, nematodes, weevils and beetles.
Downy mildew (Plasmopara viticola) can occur in most seasons, but disease severity depends upon weather conditions during the late winter to early spring period. Rainfall is essential for disease infection to occur and spread. Should warm wet weather eventuate, downy mildew spreads rapidly. Disease outbreaks can also occur during cool, overcast, moist conditions, when pre-dawn relative humidity is high with extended hours of leaf wetness.
The life cycle of grapevine downy mildew.
Sexual development (primary infection)
Oospores (resting bodies) are formed in late summer or autumn from the fungal growth within the leaves, shoots or berries. These resting bodies can survive in infected leaves and litter on the vineyard floor for five years or more. Spores are produced from the resting bodies in spring and dispersed by rain-splash onto the canopy.
Primary infection of downy mildew will occur if 10:10:24 conditions occur, when temperature is 10ºC or higher and there is at least 10mm of precipitation over a 24 hour period.
Apperance of an oilspot on the leaf
Sporulation on the underside of an oilspot
Asexual development (secondary infection)
Motile zoospores released during a primary infection event establish fungal hyphae, which grow inside the leaves to form characteristic oil spots after 4-21 days, depending on temperature. Given favourable conditions, spread of the disease from spores produced by the hyphae in oil-spots can be rapid.
Secondary infection of downy mildew will occur during warm nights where the temperature is over 13ºC, humidity is greater than 98% and foliage remains wet near dawn for 2-3 hours.
Secondary infection of downy mildew
Secondary infection on underside of leaf
Acrobat SC in combination with Penncozeb 750DF (mancozeb) or Polyram DF should be applied as a protectant program for the control downy mildew (Plasmopara viticola). A regular protectant spray program should be maintained.
Winegrapes for domestic use
Do not harvest for four weeks after application
Winegrapes grown for export
Per AWRI guidelines (Agrochemical registered for use in Australian Viticulture). Refer to www.awri.com.au for the latest information on export MRL’s.
Precaution dried grapes
Do not use Acrobat SC in vines where grapes are to be used for dried fruit.
This information is also available in the Acrobat SC Technical Manual.