UC Cooperative Extension Ventura County
669 County Square Dr. Suite 100
Ventura CA 93003
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Powdery Mildew on Oaks
A fungus can cause odd (abnormal) branch tip growth and velvet-like growth on the leaves. The fungus is a species of powdery mildew. In the case of the velvet leaves, the fungus invades the surface cells on the maturing leaf, and the interaction of host and fungus cause the velvet growth, and may also cause a bronzing or reddening of the leaf tissues. The abnormal branch tip growth occurs when the powdery mildew fungus invades the terminal bud of the branch. The fungus becomes systemic in this bud, and the subsequent growth is multi-branched with stunted, deformed, grayish-white leaf and stem tissues.