Cause Neofusicoccum arbuti (formerly Fusicoccum arbuti) (sexual form suspected to be Botryosphaeria sp.), a fungus that appears widespread on declining madrone throughout the west coast. Most infections occur through injuries from freezing, sunburn, or pruning cuts, but under ideal conditions the fungus can infect uninjured bark. All ages and sizes of madrones are affected with larger older madrones having the most mortality.
Symptoms Black or purplish areas develop in the bark of main trunks or major branches. Soon a canker develops in the discolored area. Eventually, dead bark sloughs off, leaving a sunken area surrounded by callus tissue. Wood in the cankered area is cracked longitudinally and dark masses of spores can be seen. Rapidly spreading cankers have smooth margins and no callus tissue. Cankers may spiral around, girdling and killing trunks and branches. Non-vigorous trees may decline rapidly and die in a year or two while more vigorous trees may persist for years with multiple cankers.
- Avoid injuring or weakening trees, especially during construction operations.
- Prune out and destroy cankered or dead branches. Prune about 1 ft below the cankered area.
- Although madrone is drought tolerant, consider infrequent deep watering during extended drought periods. Do not focus waterings near the trunk.
- Avoid pruning or removing surrounding trees that may be shading the trunk of madrones. Wrap trunks to prevent sunburn if this cannot be avoided or remove trees in the fall or winter.
References Farr, D.F., Elliott, M., Rossman, A.Y., and Edmonds, R.L. 2005. Fusicoccum arbuti sp. nov. causing cankers on Pacific madrone in western North America with notes on Fusicoccum dimidiatum, the correct name for Scytalidium dimidiatum and Nattrassia mangiferae. Mycologia 97:730-741.
Elliott, M., Edmonds, R.L., and Mayer, S. 2002. Role of fungal disease in decline of Pacific madrone. Northwest Science. 76:293-303.