Powdery mildew Of Magnolia

Disease Information

Powdery mildew

Symptomsand damage

Powdery mildew is a contagious fungal disease that infects plants such as magnolia trees. Powdery mildew appears as a powdery or fuzzy white growth on leaves and branches. This fungus causes the tree`s foliage to discolor, wilt and fall off the branches. Shade and mild temperatures between 60 and 80 degrees promote powdery mildew growth and -- unlike other fungal disease -- moisture is not required for this fungus to grow. Applying fungicide -- such as horticultural oil, potassium bicarbonate or neem oil -- will help control powdery mildew. Consider taking preventive measure -- proper spacing for good air circulation and avoiding excessive watering -- to keep the fungus from attacking the magnolia


Most foliar diseases develop only when leaves are frequent­ly wet, as during a prolonged rainy period or with frequent use of over­head irrigation, as is common in container nurseries. If plants are watered with sprinklers, irrigation should be managed to avoid leaf wetness dur­ing overcast conditions, at night and other times when the pathogen may be present. The spread of anthracnose, Phyllostictaleaf spot and algal leaf spots can be prevented by removing infected leaves early in disease devel­opment. Selective pruning to thin the canopy can improve air movement and light penetration, making conditions less favorable for Pestalotiopsisleaf spot, powdery mildew and algal leaf spots. If environmental condi­tions for infection persist, copper-based fungicides can be used to manage bacterial leaf spot and bacterial blight. Other fungicides may be used to manage anthracnose, Phyllostictaleaf spot and powdery mildew.

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