Galls, Diseases, and Pests - Sudden Oak Death
Phytophthora ramorum

These are all California Bay Laurel (Umbellularia californica) leaves. So what do they have to do with Sudden Oak Death? Sudden Oak Death is a water mold, and while it does not kill the California Bay Laurel tree, the lesions (sores) on the leaves are a great place for the mold to multiply. The Bay Laurel trees have both a high ability to produce more pathogen and a high population in California's coastal woodlands.

The spots on the leaves below are the lesions where the Sudden Oak Death mold has grown. When it rains, the pathogen is rinsed off the leaves and into the environment, where it can go on to infect other plants, most notably, oaks.