Background information and identification of the pathogen
Heterobasidion root rot is considered the most economically important disease of pines throughout the Northern temperate regions. In the United States it causes over 1 billion dollars in losses annually. It also has tremendous ecological impacts on forest health and productivity. This pathogen attacks the roots of trees and moves from tree to adjacent tree underground causing circles of dead trees. Once in an area, the fungus grows through the roots and expands causing greater and greater mortality. The fungus produces fruiting bodies with spores at the base of dead trees and these disseminate overland to start new infections. The disease is caused by a complex of Heterobasidion species but the species currently in Wisconsin and recently found in southeastern Minnesota is H. irregulare.