Many trees, both native and decorative, can be affected by anthracosis. These fungal diseases cause premature toasting, chipping and falling leaves. For some trees, such as Modesto Ash, Sycamore, and Chinese Ligature, this can be almost a one-year event, often causing complete defoliation. For other tree species, including local oaks, the effects depend on spring weather and / or local microclimate. Often these symptoms disappear or disappear as summer approaches to warmer drying conditions.
Weather: For many tree species, wet, cool spring conditions have the greatest impact on the severity of the infection. In Sonoma County and in the San Francisco Bay area, the late rain from April to June generally lasts and the morning mist during the same period contributes to the development of anthracnose fungi. Even a microclimate in a neighborhood or property can affect which trees become infected with some trees exhibiting minor or non-damaging leaf, while others become defoliation.
the symptoms : For oaks, leaf damage caused by anthracous infections varies from small brown spots on the leaves to large brown spots, twisted and deformed brown or dead. Severe infections can lead to the fact that the growing season in the current season becomes infected and dies again. The most obvious sign of this disease for most people is the early fall of the leaves, which sometimes continues during the summer. Complete defoliation is unusual in my experience, but 50% -75% does occur. Since anthracosis is not a problem every year, our native oaks seem to tolerate this disease very well. While it is mostly a benign disease, many property owners become fairly concerned when their oaks start to discard the leaves prematurely.
Affected trees : In the Northern California Bay area, all of our native oaks are susceptible to this disease. I think that black oak is particularly dependent on anthracosis, because it is the first oak to tear a bud in spring, making it more susceptible to infections. Oak Valley and Blue Oak are also impossible if cool wet conditions persist through the spring. Coastal live oak can also be affected, but their leather leaves seem less affected than other species. Trees affected by anthracosis at the beginning of the season can produce second flush leaves in summer if the climatic conditions that contribute to the disease have passed.
treatment :
Native California oaks generally do not need any type of treatment to fight anthracosis infections due to infrequent infections. As a rule, the disease is cyclical, with several years between several outbreaks, which can lead to some people being almost completely defoliated. Sanitation is the best treatment for local oaks, which focuses on the removal of infected plant parts, such as leaves and branches. Pruning can also help, if done correctly, removing only small twigs and dead branches. Severe pruning can damage oaks and can contribute to other diseases, such as powdery mildew, promoting uncontrolled germination. Suspended ventilation systems used in other plants or lawns, but near oaks, can also increase anthracnose frequency.
For more information about this pest and treatment options, see University of California IPM Pest. Note: http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7472.html
