Cause Pseudocercospora thujina (formerly Stigmina thujina) causes a common fungal blight on Port Orford cedar (POC). Seedstock collected from watersheds nearest to the coast, from more northern latitudes, and lower elevations developed less severe symptoms. POC seedlings from parent trees located in watersheds in the southernmost, most inland provenances, higher elevations, and lower mean annual precipitation had higher disease ratings.
Symptoms Chlorosis and defoliation of needles first appear on the lower and interior branches and proceed upward and outward. Lower branches may only have a tuft of green foliage at the distal end. Dead foliage is of various shades of brown to gray depending on how long it has been dead. Sparse, gray foliage can be found near the base of branches transitioning into brown foliage and then green tufts on the end. Some twigs and small branches are killed from being girdled by the disease.
Cultural control
- Plant trees from seed sources found to be more resistant to the disease.
- Remove affected foliage at the base of trees, however, it is not known if this will be beneficial in disease management.
- Removal of whole, severely affected trees may be helpful to protect nearby trees that are less affected.
Chemical control There is no research on the chemical control of this disease. It is suspected there may be several effective materials registered for this crop but application timing is unknown.
References Martin, D.K. 2008. Developing techniques for evaluating the susceptibility of root-disease resistant Port-Orford-Cedar to foliar and stem canker diseases (MS Thesis).
Hodges, C.S. 1982. Needle blight of Port-Orford-Cedar caused by Stigmina thujina in Hawaii. Plant Disease. 66:867-869.