Home > Crop Care provides information on handling Downy Mildew

Crop Care provides information on handling Downy Mildew

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There has been high rainfall throughout the 2010/2011 growing season, which has caused a devastating outbreak of downy mildew in Australian vineyards. According to a survey, conducted by the Grape and Wine Research and Development Corporation, 77% of growers described the downy mildew outbreak in 2010/2011 as high to extreme.

Crop Care Australasia provides information on handling Downy Mildew.

About Downy Mildew

Downy Mildew appears from wet and humid conditions. It attacks all the green parts of the vine, which prevents photosynthesis and the vine fruits from ripening.

Downy Mildew is best recognised by the circular yellow oilspots that appear on younger leaves. In favourable conditions, white down develops on the underside of these spots. The oilspots can remain active for about 90 days while maintaining active infection and the ability to spread cross vineyards.

Good control of primary infection is required for the young bunches are highly vulnerable (until berries are at least pea size) to downy mildew. It is important to minimise the risk of explosive secondary infection, which can easily happen overnight.

Fungicides to prevent Downy Mildew

Managing Downy Mildew requires a selection of appropriate fungicide sprays along with correct application timing and technique.

Pre-infection fungicides (also known as protectants or cover sprays) can protect the vines by preventing infection. This should be applied as close as possible before the infection begins. Pre-infection fungicides only protect the surface area that has been sprayed, which leaves unprotected areas at risk of downy spores. Protection may last only 3-5 days during the fast growth period.

The application of pre-infection fungicides must provide adequate chemical and volume for canopy size with maximum coverage of young bunches and lower leaf surfaces.

Post-infection fungicides (also known as eradicants or curatives) kill the disease inside the infected tissue, when applied at the right time. Post-infection fungicides do not eradicate downy mildew from the vineyard, however they have the capacity to kill off the disease while it is in developing stages – after the infection has occurred.

Post-infection fungicides are best applied as soon as possible, even after an infection event, to prevent oilspots from developing.

Crop Care Australasia explains vineyard monitoring will be very important this season. Spraying should be taken on the basis of weather and the disease risk forecasts.

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