There are more than 50 species of manzanita (Arctostaphylos ssp) in California alone. Two agents induce galls in manzanita species.
Exobasidium vaccinii, a fungus, is one of these agents. E vaccinii induces swollen, convex, bright red galls on the dorsal (top) side of many manzanita species. This round to oval gall can be as large as three-fourths of the leaf. Basidospores (reporoductive spores) are formed on the underside of the leaf in the depression created by the convex gall. This fungus is an exobasidium because the spores are produced on the surface of the plant rather than on its own fruiting body (for example, a mushroom).
The basidospores are spread by air currents and germinate on the wet surfaces of the host plants (manzanitas). Upon germination, the hyphae (fungal strands that form after germination) penetrate directly into new leaves. The hyphae can spread throughout the entire host plant and cause manzanita leaf fungus galls throughout the shrub.
E vaccinii can also induce witches’ brooms. I never saw witches’ brooms caused by this fungus. Leonard and I will need to be more alert and watch for manzanita witches’ brooms.
Found across the United States and Canada, manzanita leaf fungus galls also infect cranberries, rhododendrons, Labrador tea, mountain heather, huckleberries and certain blueberry species.
These infected manzanita plants were growing along the Chemise Trail near Redding CA (Shasta County).
In my next post manzanita galls caused by an aphid will be discussed.