Needle Cast, Rhabdocline

Rhabdocline spp

1 host plant · Fungal

Last updated

Douglas-fir needles show yellow spots developing to deep red-brown mottled areas by spring, with orange fungal structures visible on the underside; needles drop by June. Rhabdocline fungi favor cool, moist spring conditions. Avoid low-lying sites with poor drainage, space for air flow, and avoid east-side seed sources that are highly susceptible.

Avoid planting in low-lying areas with poor air drainage. Space plants for good air circulation. Remove infected material promptly and improve growing conditions to limit pathogen spread. Good sanitation, adequate spacing, and proper irrigation practices reduce disease pressure over time.

What Should I Do?

  • Avoid planting in low-lying areas with poor air drainage.
  • Space plants for good air circulation.
  • Control weeds around the bases of trees.
Full management details ↓

Quick Reference

Agent Type
fungal
Causal Agent
Rhabdocline spp
Host Plants
1
Spread
Wind-dispersed ascospores from infected needles on the tree. source: PNW Plant Disease Management Handbook
Favorable Conditions
Conifer needlecast fungi infect newly emerging needles at bud break in spring; wet conditions during needle elongation are critical for spore germination (PNW Gardeners Handbook Ch 17).
Now: Symptoms Appear - Late Fall through SpringModerate Risk

First yellow spots appear on infected current-year needles in autumn or early winter. Spots enlarge and darken through winter. By spring, spots coalesce into mottled red-brown patches. Infected needles fall by late June.

Management

Vulnerability Window

Bud break through new needle elongation (spring). Preventive fungicide at bud break when new needles are emerging.

What Triggers Infection

Conifer needlecast fungi infect newly emerging needles at bud break in spring; wet conditions during needle elongation are critical for spore germination (PNW Gardeners Handbook Ch 17).

Cultural Controls

  • Avoid planting in low-lying areas with poor air drainage.
  • Space plants for good air circulation.
  • Control weeds around the bases of trees.
  • Remove and destroy infected trees from Christmas tree plantations.
  • Avoid using east-side and Rocky Mountain seed sources.
Regional Notes

Coastal Douglas-fir provenances from west of the Cascade Range show general resistance to rhabdocline needle cast. Interior provenances planted in western Washington are more susceptible.

Host Plants (1)

Sources & References

Primary: PNW Plant Disease Management Handbook

Data Maturity
Baseline Extension data. Expert review underway.