Fir needle cast (Isthmiella abietis)
- Latin name: Isthmiella abietis (Dearn.) Darker
- French name:
- Division: Ascomycota
- Class: Rhytismatales
Damage, symptoms and biologyNeedle and shoot blights are caused by a related group of fungi (Ascomycetes), which cause more damage to coniferous foliage in North America than any other group of fungi. Severe infection can result in significant growth reduction.
Only a few of the many blight diseases in British Columbia are known to cause serious damage which is limited to increment loss; tree mortality is not known. Seedlings may be severely damaged if a high percentage of the foliage is infected. Heavily infected trees have an unsightly appearance caused by needle discoloration.
The degree of damage can be influenced by the age of the host tree; older trees are more resistant to damage and infection of older needles is eventually harmless.
Isthmiella abietis causes discoloured needles with longitudinal fungus fruiting structures forming on 2-year old infected needles surface.
Climatic conditions influence spore dissemination and germination, and thus the frequency and severity of infection. Blights are more common following wet springs. Lower branches and understory trees are frequently the most seriously blighted as the more humid conditions favour infections.
Economic damage caused by the needle blights is conjectural.
Generally two types of fruiting bodies develop during the life cycle of blight fungi:
- the "asexual", which occurs like small dots on the upper surface of the needles, e.g., Lirula punctata.
- the "sexual" fruiting body, which is generally large, occurs along the mid-ribs of the lower needle surface e.g., Lirula punctata.
Each blight has a different life history and many are incompletely known; that of Isthmiella quadrispora is presented as an example. Wind disseminated sexual spores infect needles on the newest growth from June until August, and by the following spring, the needles turn red and die. Immature fruiting bodies appear as thin, dark brown lines on the underside of these reddened needles in late summer. The following spring, the infected needles turn pale and tawny; the fruiting bodies become very dark, large and conspicuous, and split open when mature. The sexual spores are wind-borne and can infect only the new needles, thus completing a 2-year life cycle. No asexual spores are produced by this fungus.
Canadian Forest Service Publications
Information on host(s)
There are three species of true fir, Abies spp., in the Pacific region: amabilis fir, occurs west of the Coast Mountains; alpine fir, occurs generally above 1200 m along the Coast and is scattered throughout the Interior into the Yukon Territory, and grand fir, occurs at lower elevations on Vancouver Island and the adjacent mainland coast, inland to the Hope area, and in the southern region of the southwest Kootenays. Some of the many true fir needle and shoot blights also cause damage to Sitka spruce, and white spruce foliage.
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