White Powder on a Plant's Stem
Home gardeners often notice a white powdery residue on the plants in their yard or garden. Powdery mildew fungi causes this residue and affects many types of ornamental plants, vegetables and trees. While there are many types of powdery mildew fungi, the symptoms are similar in all plants. Does this Spark an idea?
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Identification
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Powdery mildew is a fungal disease that produces a white, powdery fungal coating on plants. This disease affects many types of plants, but is common on ash, roses, lilac, grape, fruit trees, shrubs, ornamentals, shade trees, forest trees and turfgrass. Powdery mildew does not cause permanent damage to host plants, but it is unsightly.
Effects
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Powdery mildew causes white powder to form on the leaves, stem, fruit, buds and flowers on plants. This powder resembles talcum powder and also causes distortion of leaves, yellowing of leaves and premature leaf drop. Infected plant buds may fail to open, as well. Fungal threads associated with powdery mildew fungi grow on only the top side of plant leaves and do not invade the tissues of the plant. Powdery mildew can be rubbed from plant stems and leaves with your fingers, but quickly returns.
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Favorable Conditions
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Certain conditions favor the development of powdery mildew. Warm, dry climates are ideal for powdery mildew development, but it is not present during the summer months when temperatures are over 80 degrees F during the day. Powdery mildew is often severe in areas where plants are crowded, with poor air circulation. Damp, shaded areas are also favorable for the development of this fungal disease because of the high humidity in these areas. Powdery mildew prefers to infect new growth on plants.
Control
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Purchasing disease-resistant plant varieties may help prevent powdery mildew. Avoid planting new plants in low, shaded areas to prevent powdery mildew. Overhead watering can increase the risk of fungal diseases, so avoid using this watering method if possible. If your plants show symptoms of powdery mildew, remove and destroy all infected plant tissue to prevent the spread of disease. When cultural practices are not enough to control powdery mildew, fungicides may be necessary. Apply fungicides every seven to 14 days to control powdery mildew.
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