Evaluation of 'alternative' materials to sulfur and synthetic fungicides for control of grapevine powdery mildew in a warm climate region of Australia

The efficacy of 'alternative' materials against powdery mildew (Erysiphe necator) was evaluated on Vitis vinifera cvs Chardonnay and Cabernet Sauvignon in a warm climate region of New South Wales, Australia. In the first season, sulfur, milk, whey, potassium bicarbonate (Ecocarb) and a mixture of potassium bicarbonate and botanical oils (Synertrol Horti Oil) alternated with whey reduced the severity of powdery mildew on Chardonnay bunches at harvest compared with untreated vines, however only sulfur provided commercially acceptable fruit at harvest with a mean disease severity of 4.2%. In the second season, none of the treatments, including sulfur, provided commercially acceptable control of powdery mildew on Chardonnay. The mean severities of powdery mildew on Cabernet Sauvignon were relatively low, with all treatments providing comparable control to sulfur in the second season. In the third season, spray programs incorporating the 'alternative' materials and sulfur were evaluated on Chardonnay by targeting specific phenological stages of grapevine growth. Programs that included sulfur from bud burst to flowering provided better disease control than those that included a mixture of potassium bicarbonate and botanical oils applied at the same stages. This highlights the importance of effective early season control of this disease on susceptible cultivars such as Chardonnay. Analysis of berry weight, pH, total soluble solids and titratable acidity of juices revealed no negative impact of the treatments.