Upper and Lower Stem Canker (Phoma Blight)

If you are growing Douglas fir seedlings in a nursery setting, watch for two distinct forms of Phoma blight. Upper stem canker turns seedling tops yellow, then reddish brown in late September or October of the first growing season. Lower stem canker appears as dark, sunken lesions at the soil line that can girdle and kill young seedlings. Both forms are driven by the fungus Phoma spp. and thrive in wet, cool conditions. Good air circulation, proper spacing, and avoiding overhead irrigation reduce risk significantly.

Prune out cankered branches at least six inches below visible symptoms, making cuts into healthy wood. Sterilize your tools between cuts. Canker pathogens typically enter through wounds, so minimize pruning injuries and avoid working on trees when bark is wet. Maintain tree vigor through proper watering and avoid stress from drought or compacted soil, which makes trees more susceptible.