Answer: Powdery mildew is the most common and possibly the most difficult disease to control on euonymus. It is caused by the fungus Oidium euonymi-japonici. Symptoms consist of a flat, white to gray growth primarily on the upper surfaces of the leaves, which can be rubbed off easily. Leaves may yellow slightly and drop, but heavy leaf drop is not a characteristic symptom. On young shoots leaves can become curled and scarred if infection is severe.
Prune and destroy heavily diseased branches. Remove and destroy fallen leaves. Plant in a sunny area, do not crowd plants, and avoid overhead watering. Chemical applications should begin before new foliage is infected. Fungicides will protect foliage from infection (by killing the mildew spores as they germinate) but will not remove the dense, white fungal growth from infected leaves. Spectracide Immunox, Ferti-Lome Liquid Sytemic Fungicide, Green Light Systemic Fungicide have systemic properties and can be sprayed less often than sulfur or copper fungicides (Camelot Fungicide/ Bactericide). When powdery mildew persists and sprays are repeated, it is recommended to rotate fungicides to decrease the chance of fungi developing resistance. Read and follow all directions on the label.
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