Downy mildew infections reported following wet weather

Examples of downy mildew ‘oil spots’ on grape leaves

Recent wet weather across a number of grapegrowing regions has led to conditions that are favourable to downy mildew infection of grapevines. Infections have been reported across some regions in SA and Victoria. Growers should take action now to minimise crop damage.

  • Monitoring – growers that have experienced wet weather should be carefully monitoring vines now for any signs of downy mildew infection. These include: golden-yellow, oily spots on leaves, which are best seen on the top side of the leaves. Generally, spots first appear as circular in shape and 8–10mm in diameter. In susceptible young leaves they can quickly grow bigger, reaching 20–30 mm in diameter in 10–14 days. More information on identifying signs of downy mildew infection, including photos, can be found in this Q&A document.
  • Treating infected vines – if signs of downy mildew infection are seen, eradicant sprays should be used.
  • Using preventative sprays – if no signs of infection are seen, preventative sprays should be applied. The ‘Dog book’ provides the most up-to-date information on spray options both for prevention and eradication of downy mildew.
  • Ensuring good spray coverage – sluccess in controlling fungal diseases depends on achieving good spray coverage. The AWRI recommends that spray equipment is well calibrated, and that spray coverage is checked using tools such as water sensitive papers.
  • Following resistance management strategies – it is essential to use fungicides from different groups to avoid fungicide resistance. CropLife resistance management strategies are outlined in the ‘Dog book’ and on the CropLife website.

Additional useful resources:

For more information about managing or preventing downy mildew, please contact the AWRI helpdesk on helpdesk@awri.com.au or 08 8 313 6600.