Why Does My Douglas Fir Looks Unhealthy?

Are the twigs and roots damaged?

Are there any chewed needles, branches could be defoliated?

Have the twigs turned brown and died back, small black fungal structures are present on dead tissue?

Are the needle tips yellowed?

Are there any orange, brown or yellow powdery masses on needles?

Strawberry root weevil and Douglas fir twig weevil are pests of Douglas fir. The latter attacks smaller branches on trees in the Pacific Northwest, sometimes killing them. Introduce parasitic nematodes into the soil to control the larvae. Spray leaves several times with pyrethrin for severe infestations of adults.

Needles chewed at their edges or devoured indicate caterpillars. Several kinds of moths are known to be attracted to Douglas firs to lay their eggs. When their hungry larvae, caterpillars, emerge to feed on tree foliage, they are capable of serious damage to the tree. Hand-picking makes a sizable dent on most caterpillar attacks if you catch the infestation right away.

Twig blight is a disease that causes these symptoms. Prune off affected parts back to live wood. Keep the tree growing vigorously with regular watering and fertilization.

Various fungi sometimes cause Douglas fir needles to develop yellow spots on their tips near fall. In spring the spots turn reddish-brown, spreading over the healthy green part of the needle so that it appears scorched. Moist conditions promote its spread.

Evergreens like Douglas fir sometimes fall victim to one of a variety of rusts caused by fungi. Some cause a powdery coating on needles, others form galls or swellings which release fungal spores to harm nearby apple trees. Usually, rusts are minor problems that do not require attention. However, a severe infection may defoliate the tree. All infected leaves should be removed. Spray leaves with sulfur prevent rust or to treat mild infections.

Sometimes soils lose their acidity over time which means the tree is then unable to take up iron from the soil. This deprivation is called chlorosis and is signaled by the yellowing of the foliage. Restore acidity to the soil by adding sulfur to it or fertilizing with a product that has iron chelates. For quick treatment, dilute this fertilizer in water and spray it directly on the foliage. To maintain soil acidity mulch with acid materials such as peat moss, pine needles, and oak leaves.