Web Blight
Rhizoctonia spp. (binucleate)
5 host plants
Last updated
This profile synthesizes data from multiple published sources. Expert field review is in progress.
You'll see browning of outer foliage in roughly circular areas on firs, with affected needles staying attached. Fine fungal webbing binds discolored needles together during moist conditions. The binucleate Rhizoctonia-like fungus is worse in Christmas tree plantations with dense spacing. Space plants for air circulation, avoid low-lying areas, and remove severely affected trees.
Avoid planting in low-lying areas with poor air drainage. Space plants for good air circulation. Remove affected tissue promptly, cutting into healthy wood. Improve air circulation by thinning dense growth and avoid overhead watering during susceptible periods. Preventive fungicide applications may help where the problem recurs annually.
Quick Reference
Management
Late spring through summer (May-August), peak in warm wet periods.
Warm wet conditions (20-25°C / 68-77°F); high humidity; rain splash disperses spores.
Cultural Controls
- Avoid planting in low-lying areas with poor air drainage.
- Space plants for good air circulation.
- Avoid planting near native stands of Douglas-fir that appear to have this disease.
- Control weeds around the bases of trees to improve air circulation.
- Pruning low in trees that have the disease only in the lower branches may allow harvest at some future date.
- Scout trees before the first shearing of the year.