Yellow laminated root rot occurs in most native conifers throughout the range of Douglas fir in British Columbia. The cause of this disease has been ascribed to a variety of Poria weirii Murr., or a species of Poria distinct from P. weirii. The fungus grows from infected to healthy roots through physiologically weakened contacting points or fusions, and the disease is most prevalent in Douglas fir because of the common occurrence of root fusion in this species. Douglas fir is susceptible at any age over six years but individual trees show marked differences in their resistance to killing by the disease. The symptom picture varies greatly between infected trees and is directly related to the resistance shown by the individual host. Inoculum may remain viable for over 50 years in stumps and roots. The fungus does not appear to spread through the soil nor does it appear to be able to penetrate healthy bark tissue. Although the control of this disease is currently important in many localized areas, several characteristics in the behavior of the causal fungus indicate that it will become more important as management of second growth Douglas fir forests becomes more intensive.

Qzte'l., During an investigation of root establishment in six to 18-year-old artificially and naturally regenerated Douglas fir on Vancouver Island, observations were made on the behaviour and frequence of Armillaria mellea (Vahl) Qukl. In an examination of the roots of over 150 immature trees, studies were made of: the ability of the fungus to attack trees in each vigor class; the relationship between the fatal disease, shoe-string root rot, and the decay, yellow spongy butt and root rot; and the factors influencing the prevalence of the disease in planted stock.Attack by Armillaria resulting in the death of the host was most frequent in trees of low vigor, but infection was observed in trees of all vigor classes in artificially and naturally regenerated stock. An analysis showed that the more vigorous the host, the more pronounced were the external symptoms of the disease. In vigorous trees, resinosis was heavy at the base of the stem (Figure 1). The cortical tissues were heavily permeated with the mycelium of the fungus and large fans of white mycelium were spread over the surface of the wood, encroaching on the living cambium (Figure 2). The typical black rhizomorphs produced by Armillaria did not occur closer than 12 to 18 inches from the advancing margin of the mycelium. Crown symptoms in these vigorous trees were often pronounced with heavy crops of small cones in the upper branch whorls, frequently coupled with prolific production of For personal use only.

Investigations of decay in Thuja plicata D. Don. in British Columbia have shown that the major heart-rotting fungi of living western red cedar on the Coast, in decreasing order of importance, are Poria asiatica (Pilát) Overh. (brown cubical pocket and butt rot), Poria albipellucida Baxter (white ring rot), Fomes Pini (Thore) Lloyd (white pitted trunk rot), Merulius sp. (brown crumbly butt rot), and Poria subacida (Peck) Sacc. (spongy white rot). In the Interior of the Province they are Poria asiatica, P. Weirii Murr. (yellow ring rot), Fomes Pini, Polyporus balsameus Peck (brown cubical butt rot), Merulius sp., and Poria subacida. Other fungi attacking the heartwood of living trees less extensively are Fomes annosus (Fr.) Cke., F. nigrolimitatus (Romell) Egel., F. pinicola (Sw.) Cke., Armillaria mellea (Fr.) Quél., Omphalia campanella (Fr.) Quél., Polyporus Schweinitzii Fr., and Coniophora cerebella Pers.On the areas investigated, loss through decay in stands 50 to 450 years of age never exceeded growth increment. It was indicated that decay in younger stands was of importance. Loss through decay and incidence of infection was appreciably higher in the Interior than on the Coast. No reliable external indications of decay in the standing tree were found.Deterioration in felled trees was caused by Poria Weirii, P. albipellucida, P. subacida, Armillaria mellea, Omphalia campanella, Fomes annosus, F. nigrolimitatus, and F. pinicola. Polyporus cuneatus (Murr.) Overh., and Hymenochaete tabacina (Sow.) Lév. were the major decay organisms of cedar sapwood and slash. Polyporus abietinus (Dicks.) Fr., P. versicolor (L.) Fr., P. semipileatus Peck, P. hirsutus (Wulf.) Fr., and Poria isabellina (Fr.) Overh. were restricted in distribution or of irregular occurrence.To assist in the identification of cultures all the major heart-rotting organisms were grown on tannic and gallic acid media. Seventy-seven species of Basidiomycetes were collected on living and dead Thuja plicata in British Columbia from 1943 to 1945.

An investigation of decay in western hemlock (Tsuga heterophylla (Raf.) Sarg.) and fir (mainly Abies amabilis (Loud.) Forb.) in the Juan de Fuca forest region of British Columbia has shown that the major organisms causing root and butt rots are the same in both species. These are Poria subacida (Peck) Sacc., Fomes annosus (Fr.) Cke., Armillaria mellea Vahl ex Fr., Polyporus sulphureus Bull. ex Fr., and P. circinatus Fr. Those organisms causing trunk rots of western hemlock, in decreasing order of importance, are Fomes pinicola (Sw.) Cke., F. Pini (Thore) Lloyd, Stereum abietinum Pers., Fomes Hartigii (Allesch.) Sacc. and Trav., and Hydnum sp. (H. abietis). These same organisms causing trunk rots of fir, in decreasing order of importance, are Fomes pinicola, Stereum abietinum, Hydnum sp. (H. abietis), Fomes Pini, and Fomes Hartigii. The logs of 963 western hemlock were analyzed in detail. Maximum periodic volume increment was reached between 225 and 275 years of age. Maximum periodic volume increment was reached between 275 and 325 years of age in the 719 fir that were analyzed. Scars were the most frequent avenue of entrance for infection. In 59% of the cases of infection studied the fungus had entered through wounds.

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