Central Otago Wine Growers: Monthly Seminar Powdery Mildew & Botrytis Control Powdery Mildew I have used the following programme for an organic grower, when powdery mildew had been a problem in the previous year. Early Season Spray Programme: Bud burst up until 2 leaves unfurled. At woolly bud stage, (before bud burst), apply one application of this sulphur / potassium bicarbonate / Codacide oil mix at 100 litres / Ha Then wait until bud burst before starting the seven day interval applications. Sulphur Potassium Bicarbonate Codacide Oil @ 6 kg / 1000 litres water @ 10 kg / 1000 litres water @ 12.5 litres / 1000 litres water (see weblink below) http://www.microcide.co.uk/downloads/directionsforuse.pdf Water Volume: @ 100 litres / Ha Frequency of application: Spray every 7 days. Monitor for disease every three days. Spray again if disease found. See photo below for early season shoot infection curled leaves / grey shoots.
Early / Mid Season Spray Programme: From 5cm shoot length. Water volume @ 150 litres / Ha Early / Mid Season Spray Programme: From 10 cm shoot length Include Phyte P @ 7 litres / 1000 litres water Water volume @ 250 litres / Ha Mid Season Spray Programme: From 20 cm shoot length until Pre-flowering. Include Phyte P @ 7 litres / 1000 litres water Water volume @ 400 litres / Ha Spray as close as possible to start of flowering. Do not spray during flowering.
As soon as the flower caps start to turn yellow, then apply pre flowering spray. Mid Season Spray Programme: Immediately Post Flowering. Flowering is the peak time for risk of powdery mildew infection. Spray again as soon as flowering has finished. Include Phyte P @ 7 litres / 1000 litres water Water volume @ 500 litres / Ha Continue this programme using 500 litres water / Ha for the rest of the season, whilst monitoring for disease every three days where possible. For conventional growers I have used the following programme: Growth Stage: 2 leaves exposed. Sulphur @ 6kg / 1000 L water + Wetter at recommended concentration (eg 0.1%). I would use this for the first two spray applications in with the tank mix, including foliar feeds and mancozeb. Work on 10 14 day interval depending on disease pressure. Water volume 150 L / Ha Growth Stage: 5 6 leaves exposed. Sulphur @ 6 kg / 1000 L water + Kindred (meptyl dinocap) @ 2.4 litres / 1000 L water + Wetter Spray interval 10 14 days depending on disease pressure
Water volume 250 L / Ha Growth Stage: Pre Flowering (Caps turning yellow) Sulphur @ 6 kg / 1000 L water + Indar (fenbuconazole) @ 1.2 litres / 1000 L water + wetter Water volume 400 L / Ha I introduce a systemic product here as this is the start of the three week peak infection window. I repeat this application as soon as flowering is complete but with sulphur @ 3 kg / 1000 L water Growth Stage: Berries Peppercorn size Sulphur @ 3kg / 1000 L water + Kindred @ 1.2 litres / 1000 L water (NO WETTER AFTER FLOWERING but codacide oil could be used) Water volume 500 L / Ha for rest of season. If any powdery is found, Kindred is replaced with potassium bicarbonate @ 10 kg / 1000 L Potassium bicarbonate has no harvest interval in England, and is a very effective erradicant of the mycelial growth on the leaf it acts as a dessicant to wash it off. It may be less effective in temperatures of over 30 C. General Approach: Use of sulphur to provide protection on leaf surface in early season sprays Addition of Kindred (meptyl dinocap) as an extra protectant product one more leaf area exposed. Introduction of systemic product (DMI) pre flowering, combined with sulphur to provide broad spectrum protection. Use systemic product two or three times during season, depending on disease pressure. Strobilurines have proven not to be effective in the two years we have had approval. Very prone to resistance, and very expensive also. Post flowering, drop sulphur rate, but use one more kindred to give protection. From this point on use monitoring and combination of sulphur + potassium bicarbonate if disease is spotted. Sulphur + pot bicarb is good if infection found, as pot bicarb eradicates fungal growth, and sulphur provides protection to uninfected leaf / fruit surfaces. Pot bicarb is not effective if used with other fungicides.
Knowledge of infection conditions is key. Ascospores from previous season will be present even if crop was not infected in previous season. These are released after 0.2mm rain (ie, a shower). Powdery doesn t need free water to enter the vine after this initial rain it requires shade. The following are results of studies carried out at Cornell Uni. Chart below shows %age of leaf area diseased. 1 x shade cloth admitted 30 40% of solar radiation 2 x shade cloth admitted 20% of solar radiation Chart below shows rate of Conidia spore production (ie speed of spread) This shows us that Powdery mildew needs shade to establish and spread. Infection often therefore starts inside the canopy. For this reason, spray penetration into the centre of the canopy is essential to gain control of, or protection from the disease. In my experience fan assisted air blast sprayers prove more effective than other types. Lipco (recycling) are not effective as they do not have a strong enough air blast to get into the centre of a canopy, and are generally not a robust machine. As a result of only 0.2mm rain being required for an ascospore release, early spring protectant applications are necessary to prevent infection.
Powdery mildew peak infection window is from 1 week prior to flowering, until 1 week after fruit set.