Analysis of epidemics of powdery mildew

Although powdery mildew is a widespread, persistent disease of grapevines that causes major crop loss and decreases wine quality, little was known about the factors that controlled the rate and development of epidemics in Australian vineyards. In 1996, it was estimated that powdery mildew caused $17 m dollars in lost production in Australian viticulture (approximately 2% of the estimated crop) despite a further $10m being spent in control measures. Premium winegrape varieties such as Chardonnay are highly susceptible. Entire crops of susceptible varieties are lost when control measures are inadequate. Shipments of grapes with as little as 3-5% bunch disease can be rejected by wineries. Each season, 4-8 protectant fungicide sprays are applied for disease control, an inefficient and costly approach that is not always successful because of poor spray application timing and technique.