Larch Needle Diseases

Meria laricis Vuillemin (Larch needle cast)

Deuteromycotina, Hyphomycetes, Tuberculariales

Hypodermella laricis Tub. (Larch needle blight)

Ascomycotina, Rhytismatales, Hypodermataceae

Hosts: Meria laricis is found almost exclusively on western larch, and rarely on alpine larch Hypodermella laricis has been reported on western larch in B.C. and on alpine larch and tamarack elsewhere in North America.

Distribution: These fungi are found throughout the range of larch in B.C.; mainly the southern interior with some collections at the coast.

Identification: Needles affected by both of these diseases suddenly turn yellow and then red-brown in the spring and early summer (Figs. 56a, 56b). Meria laricis: Infected needles are generally shed soon after they turn brown. Clusters of spores (conidia) may be visible with a hand lens on the lower surface of needles, as white dots associated with stomata. These can be distinguished from stomatal structures by staining with cotton blue. Fallen needles should be examined as they are an important source of inoculum.

Hypodermella laricis: Fruiting bodies (hysterothecia) form soon after needles are killed and turn brown, appearing as elliptical black spots (Fig. 56c). In contrast with Meria laricis, diseased needles are retained after normal needle drop in the fall (Fig. 56d).

Microscopic Characteristics:Meria laricis: Conidiophores originating from substomatal mycelial masses and emerging from the stomates in dense tufts, simple or dichotomously branched, hyaline, septate, frequently curved, up to 45 µm long, 2-3 µm wide. Conidiogenous cells monophialidic, apical or intercalary, indeterminate, + cylindrical, apertures typically produced immediately below the septa on a short sterigma. Conidia hyaline, cylindrical with a median constriction (hence, peanut- or dumb-bell-shaped), non-septate but becoming 1-septate at germination, 9-13 x 3-4 µm.

Hypodermella laricis: Hysterothecia black, elliptical, subcuticular, more or less in a continuous row, 0.5-0.8 x 0.2-0.3 µm; a basal layer of brown pseudoparenchyma subtends a plectenchymatous layer 10-15 µm thick below the hymenium; covering layer dark without an evident opening mechanism. Asci clavate, usually 4-spored, acutely pointed at maturity, 80-112 x 20-24 µm. Ascospores clavate tapering to an acute base, hyaline, nonseptate, with a gelatinous sheath 5 µm thick, 70-105 x 6 µm. Paraphyses shorter than the asci, filiform, slightly swollen at the tips. Pycnidia black, numerous, 120-300 x 80-120 µm. Conidia hyaline, elongated pyriform, 4-5 x 1 µm.

Damage: Neither of these diseases kill large trees, but repeated infections can result in growth reduction. Significant mortality of nursery seedlings has been caused by Meria laricis.

Remarks: Both diseases may be present on the same needles. The rapid onset of disease symptoms could be confused with frost damage. Frost damage, however, tends to kill both needles and young stems, and no fruiting bodies are formed. [A related fungus, M. parkeri Sherwood, Stone & Carrol, could be confused with M. laricis on Douglas-fir.] Several rust fungi including Melampsora occidentalis, M. albertensis, and M. paradoxa Diet. & Holw. are also found on larch. These can be distinguished by their spore-producing fruiting structures (aecia).

References:

Funk, A. 1985. Foliar fungi of western trees. Can. For. Serv., Inf. Rep. BC-X-265.

Garbutt, R. W. 1995. Foliage diseases in western larch in British Columbia. Can. For. Serv., Forest Pest Leaf. No. 71. Victoria, B.C.

Figures

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Figure 56a: Discoloured foliage of western larch affected by Hypodermella laricis.

Figure 56b: Needle discoloration and defoliation of western larch infected by Meria laricis.

Figure 56c: Hysterothecia of Hypodermella laricis on dead western larch needles.

Figure 56d: Dead needles infected by Hypodermella laricis retained on western larch.

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Larch Needle Diseases

Figures