Plant Disease Management Handbook

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Fir, True (Abies spp.) - Shoot Blight

Cause Two fungi, Lirula abietis-concoloris and Virgella robusta, occur infrequently on white, grand, noble, Pacific silver, and California red fir. These fungi have a 2-year life cycle. Newly emerged needles are infected but persist through the first and second growing seasons. During the third growing season, fruiting bodies and spores are produced.

Cause Unknown. It is thought that it is due to the fungus Mycosphaerella sp.; however, several other fungi colonize the affected needles but are found less frequently. They include Phaeocryptopus nudus, Phyllosticta abietina, and Rhizosphaera pini. It is unknown whether one or more of these fungi are the primary cause or simply infect necrotic needles that have died from some other factor(s).

Cause The fungus Grovesiella abieticola can cause a canker and dieback on true fir. The fungus is found growing primarily on lower branches and stems. Young trees are attacked most often, making this a more serious disease in nurseries and Christmas tree plantations than in natural stands. White fir and shasta fir are more susceptible than noble fir or grand fir.

Cause Many conifers are susceptible to drought stress especially noble fir, grand fir, Pacific silver fir, subalpine fir, Alaska yellow cedar, Engelman spruce, Sitka spruce, western red cedar, and western hemlock. Douglas-fir and incense cedar are more tolerant of drought than noble or grand fir but can have similar problems on lower elevation, south-facing or marginal sites. Newly planted trees are most at risk to drought damage. Drought-stressed trees are highly susceptible to secondary attack from insects and canker-causing fungi.

Cause Sydowia polyspora (formerly Hormonema dematioides), a fungus, has been isolated from needles with current-season needle necrosis (CSNN) from a number of Abies spp., including noble and grand fir from the PNW. The exact role this fungus plays in disease development is unknown. It has become one of the most common needle diseases on these trees in the Pacific Northwest.

Cause The fungus Melampsorella caryophyllacearum causes large brooms on true firs (Abies sp) including A. concolor (white fir), A. magnifica (California red fir) A. amabilis (Cascade fir), A. balsamea (balsam fir), A. grandis (grand fir), and A. lasiocarpa (alpine fir).

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Fir, Douglas and True - Laminated Root Rot

Cause Unknown, possibly genetic. Generally not considered a major economic problem. Found throughout the Willamette Valley in Oregon.

Cause A binucleate Rhizoctonia-like fungus, but not the same one that causes root rot or damping-off of seedlings. The disease affects grand, noble, and Douglas-fir. Concerns about the disease in western Hemlock increased substantially in 2019. Some studies have shown balsam fir and Sitka spruce may also be susceptible. The disease is worse in Christmas tree plantations with restricted air flow, close tree spacing, and dense foliage.