Heterobasidion root disease identification

pocket of pine stand with dead treesIn conifer stands, Heterobasidion root disease first appears as decline and death in a slowly expanding circle three to eight years after a thinning. Large pines and white spruce die as well as sapling-sized pine, spruce, and fir in the understory.

Heterobasidion fruiting bodies are shelf-like and grow at the base of stumps and dead and dying trees. Fruiting bodies can also be found growing under and around decomposing plant material on the forest floor. The initial, small fruiting bodies can resemble popcorn. The top surface of a mature fruiting body is reddish to dark brown with a white edge; the lower surface is white and contains pores. Finding fruiting bodies is the easiest way to confirm the disease.

shelf-like fruiting bodies growing at the base of a stumpLook-alikes are flat, shelf-like fungi with pores that also have white edges and grow on conifer stumps. However, similar fungi rarely grow at the ground line like Heterobasidion fruiting bodies do. Armillaria and red pine pocket mortality are two common look-alike diseases.

The Minnesota DNR and University of Minnesota continue to survey for Heterobasidion. If you think you have found it on your property, please consult this Heterobasidion (Annosum) Identification Guide for Minnesota Forest Managers. Report any suspect locations to your local DNR Forestry Office. Keep up-to-date on locations of Heterobasidion at this website.

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