Phytophthora Canker

A Technical Report from The Bartlett Tree Research Laboratories

Many Phytophthora species attack shade trees and landscape ornamentals causing root and root collar disease, stem cankers, and foliage lesions. Several species of Phytophthora are capable of causing stem cankers on various tree species, including common combinations like P. cactorum on beech, maple, and various fruit trees, and P. ramorum on oaks. Sometimes, Phytophthora lesions on trunks are actually an advanced root infection that has moved into the trunks as is often the case when Phytophthora cinnamomi causes ‘bleeding’ lesions in oak species.

Irrigate as needed to maintain soil moisture, but not to excess. Use tensiometers to monitor soil moisture. Avoid direct irrigation contact with the trunk by using a soaker hose instead of sprinkler irrigation. Mildly affected trees are known to recover, but if the root flare is not visible, removal of soil, mulch and ground covers is recommended. In addition to these practices, soil or bark applications of systemic fungicides help arrest further development of the disease, and in some cases, bark “shaving” to expose the canker margin can help arrest disease development.