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Plant NameTypeDescription 
Annosus root rotTrue FirDiseaseAnnosus root rot is caused by the fungus Heterobasidion annosum. This native soil pathogen is often in large old tree stumps. It can live several decades as a saprophyte on stumps and roots. Infection is mainly from airborne spores produced by conks on or in old stump hollows. Spores infect freshly cut stump surfaces or trunk wounds. Infection spreads from stumps to roots of healthy seedlings or trees that contact infected wood. Root infections may lead to root and lower bole decay, and trunk infections lead to stem decay. Infected roots may be covered by mycelium of the fungus, but usually no mycelium or conks are present. Decayed wood may be laminated or stringy with black flecks. In later stages of root infection, affected trees show crown yellowing and reduced branch growth. Trees often die as a result of windthrow. Bark beetles also often infest Annosus-infected trees. Newer trees growing between stumps of old trees are especially susceptible, and pockets of this disease increase in areas where the disease goes unnoticed and/or untreated.
Armillaria root rotTrue FirDiseaseArmillaria root rot is a fungal disease transmitted between plants by root contact. Armillaria is often found in newly cleared soils or soils which have been flooded. Symptoms typically include sudden or gradual slowing of growth, yellowish or undersized needles, needle loss, or dieback of branches. White thread-like masses of the fungus may be found beneath the bark near the crown of infected trees, and/or as shoestring-like rhizomorphs, which are dark strands of the fungus growing on or just beneath the soil surface. Honey-colored mushrooms often grow near the base of infected trees in the fall. Infected trees may also exhibit a dark black line in the infected area encircling the base of the plant. Young, stressed trees are most susceptible to infection. Armillaria-infected trees have damaged root systems and are more likely to fall in high winds. Armillaria may also make trees more susceptible to insect attack.
Current-season needle necrosisTrue FirDiseaseCurrent-season needle necrosis affects noble fir and grand fir. The cause is unknown, but appears to be a cultural problem due to a mineral deficiency. Shortly after growth begins, the current season's needles develop brown bands. These bands later turn dark or reddish-brown, and may expand to cover the whole needle. The reddish-brown needles drop from the tree. Current-season needle necrosis is not specific to a particular area on the tree. It does not spread between trees.
FlowersTrue FirDiseaseOld, spent flower parts remaining on twigs can be misinterpreted as a disease or insect problem or an unusual growth anomaly.
Grovesiella cankerTrue FirDiseaseGrovesiella canker is a fungal disease found mainly on the lower branches and stems of young trees or the lower branches of older trees. Sunken, dead areas develop on one-year-old and older branches or stems. The affected branch is swollen above the canker and twigs may die back. Young trees may die if a canker girdles the stem. The cankers continue to expand indefinitely. Cankers are not found on the crown or roots of affected trees. Grovesiella canker can be a concern on Christmas tree plantations. White fir and Shasta fir are more susceptible than Noble fir or grand fir.
Interior needle blightTrue FirDiseaseInterior needle blight is found primarily on noble fir in Christmas tree plantings, but may also occur in the landscape. While a fungus has been associated with the disease, other factors may also be involved. Needles on the lower branches turn brown, but remain attached to the branches. Affected needles are dropped by spring, resulting in minor to severe defoliation. Affected Christmas trees may be unmarketable, but damage to landscape trees is most likely only aesthetic unless the problem becomes very severe.
Needle castsTrue FirDiseaseNeedle casts on true fir are caused by several fungi. Infected trees develop brown or straw-colored needles which drop prematurely. Severely infected trees may have only current-season and one-year-old needles. The undersides of two-year-old and older needles develop elongate, dark brown to black fungal structures on either side of the midvein. The upper surface may display a single or double brown line of small dots in the midvein groove OR two distinct greenish or brown rows or wrinkles on either side of the midvein (not in the groove).
Phytophthora root rotTrue FirDiseasePhytophthora root rot is usually a problem only in areas with poor drainage or where flooding occurs. The fungus attacks the roots, which rot and die. The infection moves up into the crown, where the cambium (soft inner bark) turns reddish-brown or caramel in color instead of the normal white to greenish color. Older trees may develop cankers on the trunk, which are a dark reddish-brown when cut. The cankers may be accompanied by split bark and oozing pitch. Lower branches wilt, turn dark red, and die back. Younger trees are often killed outright, while infected mature trees may show wilting, branch dieback, and/or gradual decline.
Rust (Pucciniastrum)True FirDiseasePucciniastrum rusts are fungal diseases. Yellowish spots or blotches appear on the upper side of infected needles. White, tube-like structures are typically found on the underside of last season's needles in early summer or on current-season needles in late summer or fall. Yellow fungal spores are found inside these structures. Severely infected needles drop from the trees. Alternate hosts for Pucciniastrum goeppertianum include wild blueberry, cranberry, and huckleberry. The berry bushes develop witches' brooms with thickened stems and few leaves when infected. A reddish-brown layer forms around the infected stems. Alternate hosts for P. epilobii are fireweeds. Pucciniastrum rusts affect grand, Pacific silver, noble, balsam, white, red, and subalpine firs. Rust diseases are favored by cool, moist springs. This disease is often confused with Uredinopsis rust.
Rust (Uredinopsis)True FirDiseaseUredinopsis rust is a fungal disease. Yellowish spots or blotches appear on the upper side of infected needles. A slight discoloration may first be observed on current-season needles in fall or winter. White, tube-like structures are typically found on the underside of last season's needles in the spring and for one or more subsequent years. The white or colorless fungal spores are found inside these structures. Severely infected needles drop from the trees. All true firs can be infected by Uredinopsis rust. Brackenfern, the alternate host, shows discolored, yellowish markings on the upper side of fronds, and white fungal structures on the underside when infected. Rust diseases are favored by cool, moist springs. This disease is often confused with Pucciniastrum rust.
Balsam twig aphidTrue FirInsectBalsam twig aphids feed on needles and buds of firs. Three distinct forms of the balsam twig aphid occur. Aphids may be (1) small and yellow-green, (2) large and bluish-gray, or (3) have woolly white secretions which make them appear powdery. The aphids mat needles together and cause new growth to be deformed and stunted. Some needles are killed and drop from the tree, leaving rough twigs. A large amount of honeydew (a sticky material excreted by the insects) is produced, which may be covered with a black growth of sooty mold. Healthy trees will tolerate moderate infestations easily.
Balsam woolly adelgidTrue FirInsectThe balsam woolly adelgid feeds on the stems of true firs. White or grayish cotton-like masses, inside which are the purplish-black insects, can be found on the twigs, branches, or trunk. Heavy adelgid infestations may cover the entire trunk. The feeding insects cause the tree to form swollen, knob-like areas at nodes and tips of infested branches. Adelgid infestations weaken trees, cause foliage to become sparse, and can kill trees. This is a serious pest in the forest and the landscape on balsam, grand, subalpine, Pacific silver, and Frasier firs. Balsam fir and subalpine fir are particularly susceptible.
ConewormsTrue FirInsectConeworms attack trees by boring into shoot tips or stems, especially around wounds, and feeding on the soft bark tissues. Tip dieback may result from coneworm feeding. They may also bore into green cones, or feed on the soft bark of young growth or inside the bark on the trunk. The coneworms are small and light brown with a darker head. The adult coneworm is a mottled gray moth. Coneworms also attack pines, hemlocks, Douglas fir, and spruces.
Giant conifer aphidsTrue FirInsectGiant conifer aphids are large (up to 1/5") and dark brown to black in color. They overwinter as eggs on twigs or branches. Adults and nymphs begin feeding on stems in the spring. They excrete large amounts of honeydew (a sweet, sticky material), which may become covered with sooty mold, a black fungus.
Spruce budwormTrue FirInsectThese larvae feed on the buds and foliage and may tie shoot tips together with webbing to make a nest. They are typically green to brown in color with a darker head and grow to approximately 1" in length. The adult is a dark gray moth. Spruce budworms are mainly pests of balsam and subalpine firs. They also attack spruces and Douglas fir. This insect is an infrequent pest in the landscape.
Spruce spider miteTrue FirInsectThe presence of spruce spider mites is indicated by yellow or bronzish stippling beginning near the needle bases. Infestations usually begin on older needles of the lower branches and spread upwards as the mite population increases. Damaged needles eventually turn brown or reddish-brown. Fine webbing can cover the needles and twigs. The actual spider mites are very small and vary in color from greenish to orange, dark green, or black, with orange legs. Spruce spider mites attack many species of conifers. They are easily spread by wind and are often worse on dusty roadside trees.