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Plant NameTypeDescription 
Annosus root rotHemlockDiseaseAnnosus 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 oftentimes 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.
Phytophthora root rotHemlockDiseasePhytophthora 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. Phytophthora root rot decreases the number of lateral roots, especially on seedling trees, and causes the existing roots to turn red-brown inside. The infection moves into the crown, where the cambium (soft inner bark) turns reddish-brown instead of the normal greenish-white. Lower branches may wilt, turn brown, or die back. Young trees are often killed outright, while infected mature trees may show brown or yellow needles, wilting, branch dieback, or other signs of inhibited water and nutrient uptake. Western hemlock (Tsuga heterophylla) and mountain hemlock (T. mertensiana) are particularly susceptible.
ConewormsHemlockInsectConeworms attack trees by boring into green cones, shoot tips, stems, and trunks. They are particularly attracted to wound sites. Coneworm feeding results in the dieback of affected twigs. Injured twigs often can be distinguished by the presence of pitch and sawdust-like frass (excrement). These larvae are small (about 1/2" long) and light brown with a darker head. The adult coneworm is a mottled gray moth. Coneworms also attack pines, true firs, Douglas fir, and spruces.
Hemlock scaleHemlockInsectHemlock scales feed on the needles of Eastern hemlock (Tsuga canadensis) and spruces (especially Colorado blue). Adult scales are round to oval, dark gray or black in color, and about 2 mm (1/10") in diameter. Immature scales (crawlers) are green to yellow. Scales are typically found as small bumps on the underside of needles. As few as 4-6 scales per needle will cause the needle to drop. Colorado blue spruce in particular loses large numbers of needles. Severe infestations may weaken trees sufficiently to cause death. The hemlock scale is most common on stressed trees.
Hemlock woolly adelgidHemlockInsectHemlock adelgids are aphid-like insects. They appear as white, woolly tufts on the bark and needles. Trees with severe infestations may be stressed, predisposing them to other insect and disease problems. Needles drop prematurely, weakening the tree and sometimes leading to death. The adelgid overwinters as woolly adults, with reddish-brown crawlers similar to scale crawlers appearing in spring and early summer. Adults are black beneath the woolly material. Hemlock adelgids are sometimes known as hemlock chermes. The hemlock adelgid is especially a problem on hemlock hedges.