Rhizosphaera Needle Cast
Overview:
- Caused by several fungi species in the genus Rhizosphaera
- Impacts spruce trees
- Specifically, Colorado blue spruce, white spruce, and Oriental spruce
- Norway and red spruce are more resistant
- True fir, pine, hemlock, Douglas-fir, and true cedar can be impacted
- Trees are more susceptible when stressed by drought, or when air flow is limited and shade causes prolonged periods of wetness
- Fungus invades needles through stomata and overwinters in diseased needles. Symptoms can take 12+ months to develop.
- Spores are dispersed from spring through autumn by wind and rain
- Needles on interior branches in lower canopy are infected first, gradually spreading upwards
- Needles appear purple, then brown, then straw-colored before dropping prematurely
- Black fruiting bodies develop on needle surface
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 depend on 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.