UC Cooperative Extension Ventura County
669 County Square Dr. Suite 100
Ventura CA 93003
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Armillaria on Oaks
California live and valley oaks and Armillaria mellea (oak root fungus) both evolved in a climate of winter rains and summer drought (Mediterranean climate). When there is moisture present, winter and spring, the tree and the fungus can both grow, but the soil is cold so the fungus cannot become too aggressive. In summer and fall, when the soil dries out, the fungus goes dormant, and the oak has a chance to repair any damage using deep soil moisture not available to the fungus. In this manner the oaks and the fungus have developed a relationship in which both survive.