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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