A fallen tree at Mission Park

What is an Armillaria?

On Sunday night, August 29, the City received a call about a downed Brazilian Pepper tree at Mission Park. Upon inspection with our Urban Forestry Team and an independent contractor, the tree failed at the base due to Armillaria root rot. 

What is Armillaria? It’s a fungus that causes disease in many types of trees and shrubs. New infections occur when healthy roots grow close to diseased roots. Unfortunately, there is no treatment for Armillaria root rot. The disease can be managed by the consistent removal of dead trees and infected stumps.

Typically, the trees show signs or symptoms of this disease, which may include honey-colored or brownish-yellow mushrooms in clumps around the base of the tree, shoestring mycelium, mycelial fans, and oozing from the main stem. Unfortunately, there were no visible signs to diagnose with this tree. Staff also found white mycelium inside the center of the stump and roots (see photos). This pathogen can seriously impact the structural integrity of a tree and is what ultimately caused this specific tree to fail.

City staff will continue to monitor this area for the safety of park visitors. For more information, contact the City’s Urban Forestry Division at 805-652-4550 or [email protected].

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