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Annual Spread Rate of Tomentosus Root Disease

The spread rate of tomentosus root disease, caused by Inonotus tomentosus, was investigated by a new technique employing temporal differences in the initiation of the reduced annual radial increment between pairs of diseased trees. Pairs of infected trees (stumps) located on the periphery of disease centers were selected in each of six widely separated spruce (Picea spp.) stands in British Columbia. Distances between 12 pairs of stumps were measured, and disks were collected from each stump. Similarly, disks from four additional pairs were collected from trees in a younger stand. Uninfected control disks were collected for all sites. Tree-ring measurements were determined for all disk samples and the year in which the reduction of the annual increment attributable to I. tomentosus began was determined for infected trees. The difference between initiation years for pairs of infected trees divided into the distance between them produced an average annual spread rate of 20 cm/yr. This rate will be used in developing a model for the disease.