Blue spruce and Norway spruce are popular landscape plants in Kentucky. However, many factors can cause spruce trees to cast (shed) needles. Casting may be the result of environmental stresses (heavy soil, poor drainage) or fungal diseases. In Kentucky, Rhizosphaera needle cast is the most common disease of spruce. This disease causes needle drop on lower branches, resulting in a distinct thinned appearance. Stigmina needle cast is a less common disease of spruce, but also causes symptoms similar to Rhizosphaera needle cast. Management options for both diseases include reduction of plant stress, good sanitation practices, and timely use of fungicides.
Rhizosphaera and Stigmina Needle Cast Facts
- Symptoms become evident in summer when needles on lower branches turn purplish or brown (Figure 1). Needles fall within a few weeks and lower limbs are left bare (Figure 2).
- In order to determine whether Rhizosphaera or Stigmina needle cast is present, infected needles should be inspected with a hand lens. Look closely for the type of fungal fruiting body emerging from stomata (pores in needles) to confirm diagnosis.
Rhizosphaera needle cast – Small, dark fruiting bodies (pycnidia) appear as tiny raised, grayish bumps topped with white waxy caps (Figure 3). While most easily recognized with a hand lens, they may also be visible with the naked eye.
Stigmina needle cast – Fungal fruiting structures (sporodochia) appear as tiny, brown to black, brush-like tufts emerging from needles (Figure 4).
- Rhizosphaera needle cast is caused by the fungus Rhizosphaera kalkhoffii. Stigmina needle cast is caused by Stigmina lautii.
- Spread by water splash or wind-driven rain; moisture is needed for infection.
- If defoliation occurs over 3 to 4 consecutive years, branch death is likely.
- Stressed trees are more susceptible to infection than healthy plants, so take steps to maintain plant vigor.
- Properly space plants to improve air circulation, thereby encouraging rapid drying of needles.
- Practice good sanitation habits.
- Homeowners can apply fungicides that contain chlorothalonil, copper, or mancozeb during needle emergence (mid-April through May). During rainy seasons or in plantings with a history of disease, an additional application may be warranted. Fungicides should be applied 2 consecutive years during spring when fungi are most active.
- Spruce Diseases in Kentucky (PPFS-OR-W-24)
- Homeowner’s Guide to Fungicides (PPFS-GEN-07)
- Landscape Sanitation (PPFS-GEN-04)
By Kimberly Leonberger, Plant Pathology Extension Associate, and Nicole Gauthier, Plant Pathology Extension Plant Specialist