See:
Madrone (Arbutus menziesii) - Canker
Cause Botyosphaeria dothidea (asexual Fusicoccum aesculi), a fungus, is associated with declining madrones. Drought stress is considered a factor encouraging disease development, as is heavy flowering and berry production.
Members of the Botryosphaeriaceae fungi can occur as endophytes, pathogens, and saprophytes on a wide variety of woody hosts. Many are latent fungal pathogens that cause no symptoms under normal conditions. However, disease symptoms can occur when plants are water-stressed such as under extreme heat fluctuations or during droughts. Some species of these fungi grow well in high temperatures and at water potentials much lower than what their plant hosts can tolerate.
Symptoms Branches dieback such that limbs and twigs appear burned. Tiny black pycnidia can be seen both on twigs and leaves. Symptoms progress from branch tips downward into the rest of the tree. Symptoms are similar to that caused by other pathogens such as Phytophthora ramorum.
Cultural control
- Prune out and destroy dead branches.
- Although madrone is drought tolerant, consider infrequent deep watering during extended drought periods. Do not focus waterings near the trunk.
Reference Bennett, M. and Shaw, D. 2008. Diseases and insect pests of Pacific madrone. OSU Extension Service EC 1619-E.