We gloomily visited coastal oak woodlands, all populated with scattered dead trees. Thousands more are infected. This threat looms over 1.2 million acres of coast live oak woodlands, and millions of acres of mixed evergreen forest. Although the mortality is by far the most severe in Marin and Santa Cruz Counties, surveyors believe the syndrome is a cause of coastal oak mortality from Monterey to Humboldt Counties. Innumerable pockets of mortality exist, but by no means all are attributable to the new Phytophthora .
Trees go from apparently healthy, with green foliage, to dead in a single season.
To determine if a green tree may be infected, look for dark seeping stains in the lower 4-7 feet of the trunk. These indicate fungal activity in the bark. Also look carefully for oak blood droplets of dark liquid oozing from crevices in the bark. Under the bark surface there is a characteristic black perimeter zone line which delineates tissue killed by Phytophthora from healthy tissue. The fungus spread may be climatically limited to fog belt forests as it readily survives prolonged drought and thrives in cooler moist climates.