Cause Sphaeropsis sapinea (formerly Diplodia pinea), a fungus, has been recovered by the OSU Plant Clinic from cankers on several branches showing dieback. This fungus has not been previously reported as a pathogen of incense-cedar and is thought to become a problem only on trees that have been weakened from growing on a poor site, drought, root damage, or other sources of chronic stress. Spores produced in cankers can spread via water splash to new tissues and initiate new infections. Sporulation has been observed during the growing season, but when spore production begins and the length of time spores are present is unknown. Symptoms of this problem have been observed from Portland to Roseburg, OR.
Symptoms Symptoms have been observed on older landscape trees that have been well established. Unlike on pines, where this is primarily a pathogen of young foliage, on incense-cedar it causes branch cankers. Symptoms show up on the lower half of trees as dieback of the smaller branches; dead branches may appear intermixed with live ones on larger branches. Cankers are sunken and constricting, but are not resinous. There is a distinct line between necrotic tissue and healthy tissue at the canker margin, which is more obvious when the bark is removed.
- Prune out infected branches. Best to wait until dry weather in late summer so insects such as pitch moth are not attracted to pruning wounds. Destroy pruned-out material.
- Keep landscape trees well watered and stress-free. Also, do not overfertilize.