Rhizosphaera needle cast

Quick facts

  • This disease is caused by the fungus Rhizosphaera kalkhoffii and is probably the most common needle disease in Minnesota.
  • Trees stressed from drought, poor planting practices or other factors are more likely to suffer from Rhizosphaera needle cast.
  • Several other fungi result in symptoms very similar to Rhizosphaera and correct identification is important.

Trees affected by Rhizosphaera needle cast

Brown needles closer to the trunk with the needles at the tips of branches still green
Brown needles closer to the trunk
  • Colorado blue spruce, Picea pungens, is highly susceptible to this disease.
  • White spruce (including Black Hills spruce), P. glauca, is intermediate in susceptibility.
  • Norway spruce, P. abies, is relatively resistant.

Rhizosphaera needle cast symptoms

Two green needles with yellow and brown patches.
Mottled yellow needles
  • Infected needles may look yellow and mottled by mid to late summer. 
  • Infected needles turn brown or purplish brown by late winter or early spring.
  • Newly growing needles in the spring do not show symptoms.
  • Needles closest to the trunk of the tree (the older needles) are often discolored while the needles at the tips of the branches remain green.
  • Tiny black spots arranged in neat rows on infected needles can be seen with a magnifying glass.
    • These are pycnidia, fungal spore producing structures.
    • These may be confused with pycnidia of Stigmina lautti, which look similar.
  • Infected needles typically fall off in the summer, 12 to 15 months after the initial infection.
  • Infected trees have thin canopies.
  • Damage typically starts on the lower branches and moves up the tree.
  • After 3 to 4 years of severe infection the lowest branches may begin to die.

How to manage Rhizosphaera needle cast

A thinned down spruce tree with several needles fallen off
Rhizosphaera needle cast damage
  • Plant Norway or Black Hills spruce instead of Colorado blue spruce or Engelmann (P. engelmannii) spruce.
  • Whenever possible plant spruce trees grown from local seed sources as these plants are likely to be best adapted to the local conditions.
  • Avoid planting young spruce near old spruce trees that may be harboring fungal pathogens.
  • Reduce stress on spruce trees by watering during periods of drought and mulching the soil around the tree.
  • Do not allow lawn sprinklers to spray the spruce needles.
  • Space spruce trees to allow good air circulation around the trees.
  • Do not shear spruce as shearing creates a dense, compact growth that stays wet longer.
  • Chlorothalonil can be sprayed twice in the spring to protect new needles.
    • The first spray should be applied when needles are half the length of the mature needles.
    • A second spray should be applied 3 to 4 weeks later or as prescribed on the fungicide label. 
  • Before spraying fungicide, confirm that Rhizosphaera is the fungal pathogen causing damage by sending a lab sample to the University of Minnesota plant disease diagnostic clinic. Several other fungi result in symptoms very similar to Rhizosphaera.

CAUTION: Mention of a pesticide or use of a pesticide label is for educational purposes only. Always follow the pesticide label directions attached to the pesticide container you are using. Remember, the label is the law.

Cynthia Ash Kanner and Michelle Grabowski, Extension educator

Reviewed in 2018

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