Annosum Root Rot

This fungus may be called many names - including annosum root rot, annosus root rot, or Heterobasidion root rot – and is caused by Heterobasidion irregulare (formerly named Heterobasidion annosum and Fomes annosus). This fungus is present throughout North America, has a very wide host range, and is commonly found in southeastern U.S. forests. The fungus causes root decay, although infected trees may survive for many years after infection. Weakened roots are at an increased risk of windthrow. Infected roots generally show heavy resin leakage, and the spread of the fungus through root grafts may cause pockets of tree mortality. Fungal spores are also spread by wind, and often infect stumps from recently harvested forest stands. Annosum root rot is most common on deep, sandy soils or former agricultural land. Prevention is the best way to manage this disease, but post-treatment of stumps with borax can limit fungal spread.