Korean fir (Abies koreana) is a slow-growing 15- to 30-foot-tall evergreen often planted alone as a specimen tree or in rows as a screen. Korean fir has dark green needles, and the cones on young trees are deep purple. Korean fir prefers full sun and moist, well-drained soil. Abies koreana "Aurea" has eye-catching golden foliage. Abies koreana "Green Carpet" is a dwarf variety that grows only 2 feet tall but 6 feet wide. Generally pest-free, Korean firs may occasionally suffer from two types of blight normally associated with pine trees.
Sphaeropsis Blight of Pine
The Sphaeropsis sapinea fungus, also called diplodia tip blight, prefers pine trees, but will make itself at home in Korean fir trees, causing tiny black, fruiting bodies (spores) in the needle tips. Found throughout North America, the fungus turns the needle tips brown and causes cankers on twigs. Dead branch tips may be scattered around the Korean fir's crown and become more numerous as the infection spreads. Weakened by the disease, the tree may suffer a secondary attack from insects or other diseases, and eventually die.
Phomopsis Twig Blight
Although primarily a disease of junipers, Phomopsis twig blight, caused by Phomopsis juniperovora, also attacks fir species, including Korean fir. The infection causes the ends of the needles to turn yellow, then brown. The fungus then advances into the stems and eventually kills the whole branch. Phomoposis spores from last year infect new growth this year. Unlike most fungal spores, drying does not kill this fungus. The spores reactivate as soon as wet, warm conditions return. Phomoposis is most active in warm, wet spring and summer weather.
Remove all dead wood and clean up all plant debris on the ground. For Sphaeropsis sapinea, apply a fungicide at budbreak, and then reapply two weeks later and two weeks after that. Remove cones from the tree and ground and dispose of them to eliminate fruiting bodies of fungus and take away the spores' overwintering site. To treat Phomoposis, prune infected parts of the plant, avoid overhead sprinklers and irrigate early in the day to give the foliage time to dry. Be careful pruning and mowing around the trees because the spores can infect the tree through wounds.
To protect Korean fir from Phomopsis, apply fungicides according to manufacturer's directions when the plants first show signs of producing new growth in spring. Repeat two weeks after budbreak. Continue applying the fungicide until the new growth has matured and is protected from this fungus. The best defence against Sphaeropsis is a healthy tree. Drought conditions leave Korean fir trees especially susceptible to attack. Keep the area around the tree clean, and provide proper levels of water and fertiliser. Too much of either can weaken the tree.