The rainy season is the best time for wild mushroom foraging. Following a rain storm the mushrooms sprout in the wild. It’s also a good time to inspect the ground near the trunks of trees to identify mushrooms or fruiting bodies that may be an indication of potentially harmful fungi.
A common mushroom that is often seen near trunks of native oaks and other trees in Sonoma County is called Armillaria mellea. This honey colored mushroom can be seen in clumps around the base of affected trees. Valley Oak trees are a common species affected by Armallaria. Also known as oak root fungus, the 
pathogen can kill the cambium bark and roots which may lead to girdling of the trunk which can kill the tree. In addition, the fungus can damage the woody tissues destroying the structural integrity of the trunk and roots. This in turn, can lead to failure of the tree.
Another common pathogen that affects Sonoma County oak trees is Phytophthera. This fungus is known as a brown rot and starts in the root crown of the tree and can grow into the trunk of the tree where it kills the sapwood of the tree. Warm moist conditions contribute to the growth of Phytophthera which is why summer watering near the trunks of oak trees should be avoided. Sap on the lower trunk may indicate the presence of the fungus. 
Sudden Oak Death is caused by Phytophthera ramorum. Sudden Oak Death affects many of our native oaks including Coast Live Oaks, Black Oaks, Tan Oaks, Shreve’s Oak and Canyon Live Oak. Symptoms include mahogany colored sap exudations on the lower trunk of trees. Bark loss and cankers may also be present. California Bay trees can be a carrier of Sudden Oak Death and keeping Bay trees pruned back from oak trees can help reduce the spread of the fungus.
Some native oaks in the “white oak family” are not affected by Sudden Oak Death. These include Oregon White Oaks and Valley Oaks.
There are also a number fungi that can cause rot and decay in trees that are less common in Sonoma County. Periodic inspections by a Certified Arborist of your trees is important in identifying potential problems and reducing impacts caused by fungi.
Call TreePro for a free inspection of your trees by one of our Certified Arborists.
