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Rhizosphaera #926229

Asked March 18, 2026, 12:02 PM EDT

I have a Blue Spruce that was diagnosed with a needle cast fungus called Rhiosphaera. Affordable Tree and Shrub says that there's no known treatment for it and suggested I contact you.

Pueblo County Colorado

Expert Response

Hi Janet,

Because control of needle cast fungi is typically neither practical nor necessary since the disease causes minimal damage to infected trees, I would advise you not to treat in any way. If the initial diagnosis was correct, and you are maintaining the tree well with regular water, a recovery should be made and the effects may only be present this year. If, however, you’re continuing to see worsening issues over the growing season, I would encourage you to send a sample to the CSU plant pathology lab to see if the diagnosis changes. You can visit their website to learn more about the process and how to submit a sample: https://agsci.colostate.edu/agbio/plantclinic/.

An Ask Extension Expert Replied March 19, 2026, 2:19 PM EDT

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