Anthracnose

Watch for small, round spots with dark centers appearing on foliage, particularly on dogwoods, oaks, and maples during wet springs in Western Washington. Infected leaves develop gray or black centers with a distinct border; under humid conditions, you might spot pinkish spore masses within lesions. More concerning are lesions on leaf stems and petioles that can girdle and kill entire leaves, or crown rot starting from the base of plants where the tissue turns reddish-brown and soft. The disease accelerates when conditions stay wet for extended periods, which is common in our Puget Sound region from March through May.

Anthracnose thrives in cool, wet conditions that favor spore germination and spread. Continuous wetness for 8 hours or longer creates ideal conditions for infection, and high nitrogen fertility actually increases disease severity by promoting succulent growth. The key to management is reducing leaf wetness and improving air circulation around your plants. Space trees and shrubs to allow foliage to dry quickly after rain and irrigation; use drip irrigation rather than overhead watering; prune off infected branches and twigs during dormancy, before new inoculum works into the soil; and select resistant cultivars when available, such as Kousa dogwood selections like Stellar Pink or Celestial.