Rhizosphaera Needlecast
HIGHRhizosphaera kalkhoffii
Overview
A common fungal disease of spruce trees, especially Colorado blue spruce, throughout the Midwest and Northeast. The fungus infects current-year needles through stomata, causing them to turn purple-brown and drop prematurely. Inner and lower branches are affected first because humidity is higher there, and the disease progresses upward and outward over successive years. Severely affected trees may retain only the current year's needles at branch tips.
- Type
- Fungus
- Severity
- HIGH
- Source
- University of Minnesota Extension
Symptoms
Purple-black spots on needles visible with hand lens (rows of black fungal fruiting bodies emerging from stomata), needle discoloration from green to purple to brown, needle drop starting from interior of lower branches and progressing upward and outward, second-year needles most affected, bare inner branches with tufts of green needles only at tips
Affected Species
Geographic Spread
Treatments
Chlorothalonil Fungicide Application
Apply chlorothalonil (Daconil) or copper-based fungicide when new needles are half elongated (typically late May) and again 3-4 weeks later. Must be repeated for 2-3 consecutive years to allow recovery of the canopy.
Cultural Management
Improve air circulation by proper spacing, avoid overhead irrigation, remove heavily infected lower branches. Consider replacing highly susceptible Colorado blue spruce with more resistant species in areas with chronic problems.
Recommended Products & Tools
Helpful supplies for managing Rhizosphaera Needlecast. Always read and follow label directions, and confirm a diagnosis before treating.
Broad-spectrum protectant for many fungal leaf and bark diseases.
Preventive spray for needle cast, leaf spots, and blights.
Sharp, clean cuts to remove affected wood — a tree-care essential.
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Frequently Asked Questions
What is Rhizosphaera Needlecast?
A common fungal disease of spruce trees, especially Colorado blue spruce, throughout the Midwest and Northeast. The fungus infects current-year needles through stomata, causing them to turn purple-brown and drop prematurely. Inner and lower branches are affected first because humidity is higher there, and the disease progresses upward and outward over successive years. Severely affected trees may retain only the current year's needles at branch tips.
What are the symptoms of Rhizosphaera Needlecast?
Purple-black spots on needles visible with hand lens (rows of black fungal fruiting bodies emerging from stomata), needle discoloration from green to purple to brown, needle drop starting from interior of lower branches and progressing upward and outward, second-year needles most affected, bare inner branches with tufts of green needles only at tips
Where is Rhizosphaera Needlecast currently found?
Rhizosphaera Needlecast is currently active in Colorado, Connecticut, Iowa, Illinois, Indiana, Kansas, Kentucky, Massachusetts, Maryland, Maine, Michigan, Minnesota, Missouri, Nebraska, New Hampshire, New Jersey, New York, Ohio, Pennsylvania, Rhode Island, South Dakota, Virginia, Vermont, Wisconsin, West Virginia. It has been reported in 25 total states across the United States.
What plants are affected by Rhizosphaera Needlecast?
Rhizosphaera Needlecast affects Balsam Fir, Colorado Blue Spruce, Norway Spruce. Susceptibility varies by species.
How do I treat Rhizosphaera Needlecast?
Treatment options for Rhizosphaera Needlecast include: Chlorothalonil Fungicide Application, Cultural Management. Treatment approaches may include chemical, biological, cultural, and mechanical methods depending on the severity and context.