Pathology > Forest Pathology > Root Disease

Root Diseases

Armillaria Root Disease
Laminated Root Rot
Tomentosus Root Disease
Annosus Root Disease

Root Disease

Root disease is a condition that occurs when a pathogen, beginning on the roots of a plant species, adversely affects the growth and survival of the affected plant. Several root diseases effect significant losses in Canada's forests and all are caused by fungi. Most are widely distributed, but each root disease has a range of host species and specific niches or zones where they are most successful. This relative specificity means that root disease fungi are influenced significantly by climatic conditions and by forest management practices.

Root diseases cause mortality but more commonly cause growth loss. This picture shows how Armillaria Root Disease affects growth of Douglas-fir. Even though both trees were initially growing at about the same rate the stem disk from an infected tree (right) is about 30% smaller than the stem disk from a healthy tree (left).

Most root disease fungi are long lived and the diseases they cause spread slowly. As a result, most root disease infection goes unseen, aboveground. Productivity losses caused by root diseases include mortality and growth reduction. The widespread distribution of root diseases in Canada's forests make them one of the most important but least seen biological agents affecting forest trees.

Root disease fungi have the ability to colonize living root systems. After they have killed a tree or the tree is harvested, these fungi continue to use the colonized roots as a food base. From this energy-rich food base they can transfer to new host trees by root contacts, by specialized fungal structures (e.g. rhizomorphs of Armillaria spp.), or by spores released from fruiting bodies (e.g. conks of Heterobasidion annosum). Factors affecting the spread of root diseases on infested sites include the rooting habit of trees, the timing of root contacts, the tree species that regenerate, and the amount and size of infested stumps. Each of these factors is further influenced by a site's soil conditions and the silvicultural practices applied there. The activities of other disturbance agents such as weather and insects also can predispose trees to the effects of root disease.

Root diseases are generally managed by using non- or reduced-susceptible tree species on infested sites or by removing fungus-infested stumps with equipment such as an excavator. Both management strategies are constrained by site suitability factors including slope, soil moisture, and soil type.

Removal of infected stumps and large roots by push-falling eliminates most inoculum from infested sites and minimizes carry-over into the new stand.