Management
First and foremost, limiting environmental factors that promote infection are key to managing powdery mildew on grapes. Optimal sites feature full sun on all grape structures and ample aeration to reduce humid microclimates under shading leaves. Pruning vines and clusters and planting on a gentle slope and orienting in rows running North and South promote full sun and aeration. Dusting leaves and berries with lime and sulfur was effective in 1850’s during the epidemic Europe.
Current organic agricultural practices still use a sulfur formulation as a treatment for powdery mildew. However, some cultivars like Concord are susceptible to phytotoxic damage with sulfur use. Since the fungus grows on tissue surfaces rather than inside epithelial cells, topical applications of oils and other compounds are recommended. Integrated pest management programs are utilized by organic and conventional agriculture systems, while the latter prescribes the addition of fungicides.
Typical applications of fungicides occur during prebloom and for 2–4 weeks post bloom. If the previous year was a conducive environment for infection or the current year had a warm winter, earlier sprays are recommended due to a potentially higher amount of overwintered cleistothecia. If warm and humid, conidia are produced every 5–7 days throughout the growing season. To limit powdery mildew resistance, growers alternate treatments by employing multiple modes of action.
Read more about this topic: Uncinula Necator
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