The Initiation and Spread of Poria Weirii Root Rot of Douglas Fir

Abstract

Root rot caused by Poria weirii Murr. occurred when healthy roots of Douglas fir came into contact with inoculum in infected roots of the previous stand. Mycelium grew ectotrophically on the bark of the Douglas fir roots, frequently well in advance of growth in the wood, and penetrated to living tissues directly through sound as well as injured bark. Spread of the disease to adjacent trees took place where healthy and diseased roots were in contact, the mycelium apparently spreading to only a very limited extent through natural soil. It was shown that mycelium could invade roots of trees felled for at least 12 months and Douglas fir heartwood that had been buried in soil for at least 12 months. Viable Poria mycelium was isolated from infected roots as small as 2 cm in diameter 11 years after the trees had been cut. While Douglas fir and western hemlock appeared to be quite susceptible to infection, western red cedar, red alder, and bigleaf maple showed considerable resistance.

Western redcedar—a literature review.

“…Furthermore, nonredcedar isolates are less able to parasitize western redcedar than isolates from the redcedar race (Morrison 1969). Ectotrophic mycelia are nearly absent on redcedar roots infected with P. weirii (Wallis 1976), and western redcedar is quite resistant to the fungus (Wallis 1962, Wallis andReynolds 1967). In northern Idaho, the resulting decay usually is restricted to the first log (Canfield 1969).…”

Impact of root rot and other diseases in young Douglas-fir plantations

“…Spread of Poria weirii can continue throughout the rotation, and infection inevitably leads to death (Wallis and Reynolds 1965). Where infection centers are common in young stands, losses by the time of harvest will undoubtedly be high.…”

“…and standing and down mortality. Having located infection centers in this manner, we then examined .,ie root collar and upper roots of surrounding trees for lesions and mycelium typical of the fungi involved (Wallis and Reynolds 1965, Wallis and Ginns 1968, Foster and Baranyay 1971 ). Decays not readily identifiable in the field were returned t o the laboratory for cultural identification.…”

The Effect of Decay on Growth Rate in a White Spruce Plantation

“…Losses in merchantable volume of the above-mentioned species were 11, I I, and 80h respectively, as a result of butt rot, and were 10, 12, and 5% respectively of the annual increment as a result of growth reduction associated with root rot. Wallis and Reynolds (1965) noted variable leader growth reduction on individual Douglas fir trees (Pseudotsuga menziesii (Mirb.) Franco) with their root systems infected by Poria weirii Murr.…”