Phytophthora root and crown rots are very common in landscapes this year. The following is more information.
Phytophthora root, crown, and collar rots are common and destructive diseases of trees throughout the world. Trees declining from Phytophthora root and crown rots are frequently diagnosed as suffering from"wet feet" (mistakenly assumed to be root asphyxiation or "drowning"), and sometimes are confused with those suffering from winter injury.
Diseased trees are most likely to be found in heavy, wet soils or areas where water collects or is slow to drain . Above-ground symptoms are variable among tree species and locations, but include poor growth with sparse off-color foliage, wilt, and collapse. Infected trees may decline over more than one season, and gradually-declining trees often show abnormal or premature coloration of the foliage in early autumn. In other cases, previously-healthy trees may suddenly collapse and die shortly after resuming growth in the spring, especially if the previous autumn was excessively wet. Similarly, previously-healthy trees may suddenly collapse during the latter part of the growing season following a very wet spring.
A diagnostic reddish brown discoloration of the inner bark can be seen by removing several inches of soil around the base of declining trees and cutting away the outer bark layer on the exposed crowns; often, it's possible to see a sharp contrast between the infected and healthy (white) crown tissues. The inner bark of larger infected roots often shows a similar discoloration. These symptoms distinguish Phytophthora root and crown rots from other common causes of decline and collapse.
Red coloration under the bark on a Phytophthora infected tree.
Information adapted from Kearneysville KTFREC - Fruit Disease Focus - Phytophthora Root, Crown, and Collar Rots, West Virginia University