Rhabdocline Needle Cast
Overview:
- Foliage disease caused by fungi in the genus Rhabdocline
- Primarily impacts needles of Douglas-fir (Pseudotsuga menziesii) from seedling stage to 30 years of age
- Outbreaks are associated with abnormally cool temperatures and high precipitation in the spring and summer months
- Severity of the disease is linked to closely spaced trees
- Symptoms appear in late fall or early winter and include yellow spots or flecks on needle surfaces
- The spots gradually get bigger and turn reddish brown
- Symptoms are most severe on the lower portion of the tree
- In late spring, fruiting structures of the fungus develop on the lower surface of the needle below the epidermis
- Epidermis splits open and exposes fungal spores, which are spread by wind and rain
Management:
Cultural Practices:
- 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
Materials:
- 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 dependon history of disease severity
- Cover needles thoroughly for effective treatment
- Canopy penetration is critical
- Must follow allowable Ai/acre



Disclaimer – Materials do not cover all possible control scenarios and are intended for licensed professionals. Tradenames do not imply endorsement and are used as examples. You must strictly follow the label for each compound prior to use. Rutgers is not responsible form is used materials or damages thereof. The label is the law. Labels will provide detailed information on use and restrictions. Additionally, application intervals, compatibility, surfactant use, PHI, PPE, important and other key information is described in detail. Always discuss treatments with your local agents. Note: Neonicotinoids can only be legally applied in commercial agriculture settings by licensed applicators. Guidelines and recommendations made in this presentation are specific to the state of New Jersey.