Research has shown that these symptoms - shown above - are caused by Rust mite feeding on developing shoots and bunches during the early phase of shoot development. Yield losses have been recorded of up to 30% in other states, but the greatest effect is on evenness of shoot development and thus end fruit quality.
An unbalanced vineyard predatory insect population is thought responsible for high numbers of Rust Mite. If you are seeing this take a look at your spray practices.
Bronzed leaves at harvest are another indicator of high levels of Rust Mite - Below.
Recommendations for prevention of these symptoms are:
• Application of wettable sulphur @ 500g/100lt (include non ionic wetter at label rate if not adding oil).
• Water rates of 600 – 900 lt of water per hectare - do not use less than 500 lt/ha
- increased water rate should be used if worried about coverage.
• Make sure coverage of the cordon and all spur wood is thorough.
• Inclusion of Canola oil or Mineral oil at 2% (2lt per 100 lt) may improve control (10-15%) but should only be applied if the variety being sprayed is fully dormant (eg. Cabernet). Need to be aware that some Canola oils may contain GMO’s.
• A period of 2-3 fine days and 15 degrees C or higher on the day of spraying is ideal.
• Chardonnay is the indicator variety for timing of spraying in each region. Spraying should be done on all varieties when Chardonnay reaches 10% green tip (i.e. most buds woolly bud).
• Our feelings are that spraying should occur from now until the end of the first week of September on all varieties/blocks inthat require rust mite treatment.
Any questions about timings for your specific region please call DJ's for more advice.