Tree Disease - Rhizosphaera Needle Cast

Scientific Name: Rhizosphaera kalkhoffi

Rhizosphaera needle cast is a foliage disease of spruce trees. It causes significant damage to trees growing outside of their native range. Older, inner needles show symptoms first. As the disease progresses, newer needles will exhibit symptoms. Infected needles first appear mottled or speckled with dull yellowish blotches. Later, the needles turn brown to purplish brown. The needles are dropped (cast) anywhere from 3 –15 months after infection depending on the variety of spruce infected. Branches begin dying if they are defoliated in 3-4 consecutive years. Larger trees are rarely killed, however they may become so disfigured that they lose all of their ornamental value.

 
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Rhizosphaera Needle Cast

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Attacks: Colorado spruce, white and black hills spruce

 
What you will see:

 

  • Thin trees with lower branch dieback
  • Excessive thinning/ dropping of older needles
  • Black dots in the stomata on the underside of the needles
  • Yellow and purple/brown needles

 
Life cycle:

 

  • Needles are infected with the pathogen in spring during wet weather
  • New needles are susceptible to disease - all year long
  • Fallen needles produce spores that re-infect healthy needles
  • Wet and/or humid conditions promote disease

 
Management of Rhizosphaera Needle Cast
 

Cultural practices:

 

  • Reduce moisture adjacent to tree
  • Move sprinkler heads
  • Do not water foliage
  • Increase air flow through canopy
  • Prune out infected tissue
  • Remove fallen needles
  • Do not plant Colorado spruce

 
Chemical Treatments:

 

  • Treat foliage with fungicide to prevent infection
  • Make sure treated trees will not continue to be in contact with moisture
  • After treatment needles may continue to change color and fall off, since infection occurred prior to treatment.