Spruce Dieback – Needle Cast Diseases May Be To Blame

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 multiple Stigmina
  • 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.
Figure 1: Needles infected with Rhizosphaera turn purplish brown during summer. (Photo: Julie Beale, UK)

Figure 1: Needles infected with Rhizosphaera turn purplish brown during summer. (Photo: Julie Beale, UK)

Figure 2: Needle drop and thinning of lower canopy are classic symptoms of Rhizosphaera needle cast in spruce. (Photo: Minnesota Department of Natural Resources Archive, Minnesota Department of Natural Resources, Bugwood.org)

Figure 2: Needle drop and thinning of lower canopy are classic symptoms of Rhizosphaera needle cast in spruce. (Photo: Minnesota Department of Natural Resources Archive, Minnesota Department of Natural Resources, Bugwood.org)

Figure 3: Rhizosphaera pycnidia appear as tiny raised, grayish bumps topped with white waxy caps. (Photo: Paul Bachi, UK)

Figure 3: Rhizosphaera pycnidia appear as tiny raised, grayish bumps topped with white waxy caps. (Photo: Paul Bachi, UK)

Figure 4: Tiny, brown to black, brush-like tufts emerge from infected needles through stomata of needles infected with Stigmina. (Photo: Paul Bachi, UK)

Figure 4: Tiny, brown to black, brush-like tufts emerge from infected needles through stomata of needles infected with Stigmina. (Photo: Paul Bachi, UK)

Management Options

  • 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). During rainy seasons or in plantings with a history of disease, fungicides may be applied 2 consecutive years during spring when fungi are most active.

Additional Information

 

By Kimberly Leonberger, Extension Associate, and Nicole Ward Gauthier, Extension Plant Pathologist

 

Posted in Landscape Trees & Shrubs