a root disease caused by the white rot fungus Heterobasidion annosum mostly on conifers, characterized by a light-yellowish stringy decay of the roots and butt, thinning crowns, and windthrow —note the fungus spreads from tree to tree by root contact; the disease tends to occur in patches of trees that enlarge progressively with infection centers often beginning in freshly cut stumps This definition last updated 10/23/2008