What are the symptoms of sudden oak death and related diseases?
In oaks, the first symptom is typically a bleeding or oozing of thick, dark reddish-brown sap from the trunk. With tanoaks, the first symptom is dropping of new leaf growth. Beetles then attack the weakened trees, and in the later stages of decline, decaying fungi are seen on the trunks of oaks and tanoaks. An infected oak will form a girdle, or ring of dead tissue, beneath the bark of its trunk, which blocks the flow of water and nutrients. A tree may be infected for several years before it dies, although in the final stages of the disease the foliage may turn from green to brown in just a few weeks. Signs of the disease caused by P. ramorum in redwood have been observed only in the needles and very small branches of redwoods. In redwoods, the infected sprouts became yellowed and discolored. Douglas fir seedlings showed a similar, but more intense, response. How do scientists know that these diseases are caused by P. ramorum? First they take living cultures or DNA samples from trees t
