Needle Cast Diseases

There are many diseases that impact conifer foliage
Particularly harmful to Douglas fir and spruce trees
Causes needles to turn brown, yellow, or purple, and eventually drop prematurely, leading to sparse or bare branches
Stressed trees are more likely to suffer – can lead to death
Makes trees more susceptible to other pests and diseases
Symptom development often not observed until next season
- New growth is infected, lifecycle completes following season, and is ultimately ‘casted’ from tree

Inspect stock being planted
Remove severely infected tree prior to crop bud break (30%+ infected)
Prune infected branches during DRY weather, disinfect pruning tools between cuts
Avoid overhead irrigation
Promote air circulation
Mulch to moderate soil temperature
Fertilize to support tree’s natural defenses (not too much N though!)
Reduce plant stress

Contact fungicides:
- Chlorothalonil [M05]
- Mancozeb [M03]
- Coppers [M01]
Systemic/Translaminar fungicides:
- Propiconazole [3]
- Azoxystrobin [11]
- Thiophanate-methyl [1]
- Combination products
Considerations:
- First application in the spring when candles half-elongated / ½”
- Second application 2-3 weeks later (unless high pressure/wet, then 10-14d later)
- Continue applications every 2-4 weeks (total of 3-5 sprays)
- Total # of applications depend on history of disease severity
- Cover needles thoroughly for effective treatment
- Canopy penetration is critical
- Must follow allowable Ai/acre