By Andi Anderson
Christmas tree farms are facing growing losses due to Armillaria root rot, a fungal disease caused by several Armillaria species. These fungi affect hundreds of woody plants and are now a major threat to tree plantations.
Armillaria damages tree roots, cuts off water and nutrients, and often kills trees within a year or two. The fungus can infect even healthy trees and remain active in stumps or soil debris for decades.
Early symptoms include needle fading and browning. Diagnosis requires examining the roots and lower stems. Look for white, fan-shaped mycelial growth under bark or black string-like rhizomorphs in the soil.
Mushrooms can appear at the tree base in cool, wet weather, but they’re short-lived and not always present.
“Rhizomorphs… are one of the primary ways Armillaria invades new host trees, even in the absence of direct root-to-root contact,” researchers explain.
Armillaria spreads in two main ways: by growing from tree to tree through root contact and by spores that travel through the air. Once established, it can spread several feet each year underground.
Currently, there is no reliable chemical control for this disease. Michigan State University Extension recommends removing infected stumps and not planting trees nearby.
Ongoing research aims to identify resistant tree species using rapid screening methods. For now, good sanitation and early detection are the best tools available.
To protect plantations, growers must stay alert for signs of infection and avoid replanting in areas where Armillaria has been found.
Photo Credit: michigan-state-university-msu
Categories: Michigan, Crops