Annosum Root Rot - Introduction

Annosum root rot, caused by the fungus, Heterobasidion annosum was first identified in Wisconsin in 1993 and is considered among the most important and destructive diseases affecting conifers in the north temperate regions of the world. Over 200 woody species have been reported as hosts. Red, white and jack pine and white spruce are the species most likely to be infected; particularly in plantation-grown stands subjected to thinning.

Annosum has been confirmed in twenty counties including Adams, Buffalo, Columbia, Dunn, Green, Iowa, Jefferson, Juneau, LaCrosse, Marquette, Portage, Richland, Sauk, Shawano, Trempealeau, Walworth, Waukesha, Waupaca, Waushara, and Wood counties.

Site Factors/Stand History

In the southeastern United States, disease development is more common on land formerly used for agriculture and with a pH >6 than on old forest soils. Sandy or sandy loam soils at least 12 inches (30 cm) deep, with good internal drainage and a low seasonal water table are also considered sites favorable for disease development. The influence of site factors on disease progression has not yet been studied in Wisconsin. Annosum root rot is most damaging in plantation-grown conifers where thinnings provide infection courts (fresh stumps) and root grafts provide a pathway for Annosum to move from tree to tree.