Elytroderma deformans (Weir) Darker
(= Hypoderma deformans Weir)
Ascomycotina, Rhytismatales, Hypodermataceae
Hosts: This disease is restricted to "hard" or "two- and three-needle" pine species. In B.C., Elytroderma deformans has been eported on lodgepole and ponderosa pine. Elsewhere in North America it has also been found on big-cone, jack, Jeffrey, knobcone, Mexican stone, pinyon, and short-leaf pine.
Distribution: Most collections of this disease are from the central interior and Kootenays. Minor damage is reported for the coast and Yukon; little or none from the north central interior.
Identification: Infection takes place in the late summer but symptoms do not appear until early spring of the following year. Groups of needles turn red and die, forming conspicuous flags (Figs. 51a, 51b). The fungus is perennial in the twigs, often stimulating them to form relatively small, open and tufted witches brooms (Figs. 51c, 51d). Fruiting bodies develop as small dark streaks on the dead foliage (Fig. 51e).
Microscopic Characteristics: Ascomata appear as narrow, black lines of varying lengths, chiefly on the abaxial surface of the browned needles, up to 10 mm long; opening by a longitudinal slit to expose the pale brown hymenium. The subepidermal clypeus of black cells covers only the central part of the hymenium. The subhymenium is hyaline and thin. Asci saccate to fusiform-clavate, 8-spored, 140-240 x 30-45 µm. Ascospores hyaline, cylindric, 1-septate, 90-120 x 6-9 µm, with thick gelatinous sheath. Paraphyses filiform, simple, septate. Conidiomata concolorous with needle, subepidermal, up to 1.2 mm long, blister-like. Conidiophores 12-15 µm long, arising from a thin basal layer, ampuliform, simple. Conidia terminal, hyaline, bacillar, 6-8 x 1 µm.
Damage: Damage is caused by branch and stem deformation, and growth reduction resulting from defoliation. Although the impact of the disease is highest on young trees or trees with poor crowns, infected mature trees may be predisposed to root disease or bark beetle attack. Diseased trees are also considered to have negative visual impact in high-value recreation sites.
Remarks: The incidence of this disease is highest where moist environmental conditions prevail, often near lakes and streams.
Hunt, R. S. 1978. Elytroderma disease of pines. Can. For. Serv., Forest Pest Leaf. No. 27. Victoria, B.C.
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Figure 51a: Discoloured needles resulting from infection by Elytroderma deformans.