Impact and management of Heterobasidion annosum vary among the forests of North America (Tables 23.1, 23.2 and 23.3). In south-eastern Alaska, the major hosts are Tsuga heterophylla and Picea sitchensis. Incidence of H. annosum in thinning stumps and subsequent mortality of adjacent trees is minor, probably because of low temperatures and high precipitation. Butt and stem decay caused by H. annosum occur in old-growth forests, where it is ecologically important. Because of the relatively low amounts of mortality, no stump treatments are used in Alaska. Prevention of wounds on residual trees during harvesting operations is encouraged. There are no reports of H. annosum in the boreal forests of interior Alaska. In British Columbia the principal hosts for H. annosum are Abies amabilis, Picea sitchensis and Tsuga heterophylla. Butt and stem decay occur in old-growth trees. Although incidence of infection of cut stumps can be relatively high, tree mortality is not common. Stump treatments with borax to reduce the incidence of spore infections have been tested and recommended in coastal British Columbia. The fungus has not been recorded from the sub-boreal and boreal forests of the Canadian prairie provinces or the northern territories. In the western USA the principal hosts for H. annosum are Tsuga heterophylla, T. mertensiana, Picea sitchensis, Pinus ponderosa and several true fir species. Butt and stem rot are more common along the coast, whereas tree mortality is more common in the interior. Infected trees are often also attacked by bark beetles, especially in the interior. Although many materials have been tested as stump protectants, only borax is recommended and used operationally. Control measures aimed at wound prevention and short rotations have been recommended to minimize stem decay by H. annosum. in south-eastern Canada and the north-eastern USA, the principal host is Pinus resionas, especially in young plantations that have been thinned. Several materials have been tested as stump protectans, with borax being the most successful. Some testing has been done with soil fumigants and with biologicals such as P. gigantea. Thinning modifications and the use of less susceptible tree species have also been recommended. In the south-eastern USA, the major hosts for H. annosum are Pinus taeda and P. elliottii, especially in thinned stands. Tree mortality is often associated with bark beetles. In addition to mortality and windthrow, H. annosum has been shown to reduce tree diameter and height growth. As in other regions, several chemicals have been tested as stump protectants, with borax and urea being the most successful. P. gigantea has also been shown to be an effective and economical method of protecting stumps from spore infection. Prescribed burning and silvicultural control have also been tested. Disease severity has been correlated with certain soil factors in the south-eastern USA. Several species of pine are hosts of H. annosum in Mexico and Central America, but more surveys and research are needed in this vast and varied region.
