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At first, yellow spots appear on the upper side of leaves. At later stage of the disease, a whitish, later greyish, floury covering spreads on leaves, stalks and fruits. The fungus extracts nutrients from the plant and the ash-like layer on the leaves hinders photosynthesis, resulting in stunted plant growth. As the disease progresses, infected parts shrivel, leaves fall off and plants might die. As opposed to Downy Mildew, Powdery Mildew can be controlled to some extent.
Fungal spores overwinter inside leaf buds and other plant debris. Wind, water and insects transmit the spores to nearby plants. Even though it is a fungus, powdery mildew can develop rather normally in dry conditions. It survives at temperatures between 10-12°C, but optimal conditions are found at 30°C. In contrast to downy mildew, small amounts of rainfall and regular morning dew accelerate the spreading of powdery mildew.
For gardens, milk-water solutions seem to work as natural fungicide. Apply this solution to the leaves every second day. This household remedy works especially well with cucurbits (cucumber, zucchini, pumpkin) and berries. The types of powdery mildew differ according to the host, and this solution may not be effective for all types. If no improvement is observed, try garlic or sodium bicarbonate solutions. Commercial biological treatments are also available.
Always consider an integrated approach with preventive measures together with biological treatments if available. In view of the number of crops that are susceptible to powdery mildew, it is difficult to recommend any particular chemical treatment. Fungicides based on wettable sulphur, carbendazim, triflumizole, myclobutanil or dinocap, seem to control the growth of the fungus in some crops.