Environment
Powdery Mildew thrives in warm, moist environments and infects younger plant tissues like fruit, leaves, and green stems and buds. Free water can disrupt conidia and only requires a humid microclimate for infection. Most infection begins when spring rain (2.5mm) falls and temperatures are approximately 15°C or higher. Rates of infection decline at temperatures higher than 30°C, since the evaporation of water occurs readily. Cooler conditions, such as shading and poor aeration, promote infection due to a higher relative humidity, optimally 85% or greater. However, sporulation does occur at levels as low as 40%. Spores are dispersed mostly by wind and rain splash.
Young underdeveloped tissues are most susceptible to infection, primarily leaves and fruit. Warmer weather cultivars like Vitis vinifera and French hybrids provide overwintering protection in buds and during moderate winters climates. American cultivars are generally less susceptible to infection unless an unusually warm winter does not kill the cleistothecia in buds. Most cleistothecia survive on the vine where ample protection is provided in the bark.
Read more about this topic: Uncinula Necator
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