Forest Health -
insects and disease
Forest health is a major concern in eastern Washington. Overstocking, drought, and exploding populations of natural and exotic pathogens combine to put pressure on these forests. This section will discuss a few of the most common problems that you may encounter.
Bark Beetles
Bark beetles such as mountain pine beetle, western pine beetle, and Douglas-fir beetle attack stress-weakened trees by boring into the bark and killing them. Trees that are already infested cannot be saved. By learning to identify the signs and symptoms of beetle infestation you stand a greater chance of saving those trees which are not yet infected. The best way to reduce bark beetle damage is to thin forest stands to improve tree vigor and provide resistance to bark beetle attack.
For more information on identifying bark beetle infestations check out the following:
Major Bark Beetles of the Intermountain West
Defoliating Insects
Defoliating insects eat the foliage of certain host tree species. The two insects of greatest concern in eastern Washington are the western spruce budworm and the Douglas-fir tussock moth which feed primarily on Douglas-fir and grand fir, but may feed on other species as well. Direct control is often not practical. Retain less susceptible species, such as pine and larch.
For more information on identifying defoliating insect damage:
Major Defoliating Insects of the Intermountain West
Dwarf Mistletoe
Dwarf mistletoe is a parasitic plant which infects most coniferous species. It seldom kills the tree outright, but mistletoe does reduce tree vigor making the tree susceptible to other damaging agents. Look for dense abnormal “broom like” clumps of foliage—known as witches brooms—which may appear like a bird’s nest from a distance. Heavy infection will eventually kill the tree. Remove heavily infected trees and/or remove infected limbs from lightly infected trees. Mistletoe is a parasite so killing the tree also kills the mistletoe plant. Trees can be killed through girdling and left as a valuable wildlife snag.
For more information on dwarf mistletoe:
Root Diseases
Root diseases such as Armillaria, Annosus [link], and Laminated [link] root rots, are caused by fungi which attack the roots of Douglas-fir, grand-fir, and some pine species. Look for trees with crowns that have yellowing foliage, thinning foliage, or reduced height growth. Trees in pockets of root disease may show varying stages of decline. Remove infected trees along with neighboring trees which are likely to also be infected through root contact. Replant with root rot resistant species.
Photo by: G.W. Wallis, Bugwood.org
Environmental Stresses
Photo by: Minnesota Department of Natural Resources Archive, Minnesota Department of Natural Resources, Bugwood.org
Diagnose your sick trees with the following resources:
WSU Plant & Insect Diagnostic Laboratory – Puyallup R&E Center
WSU forest-health on-line diagnostic
OSU common insect and disease problems
On-line catalog of western forest insects and disease
A field guide to diseases and insect pests of Northern and Central Rocky Mountain Conifers
In this section:
- Bark Beetles
- Defoliating Insects
- Mistletoe
- Root Diseases
- Environmental Stresses
- Diagnostic Resources
Possible indications of bark beetle activity:
- Large amounts of pitching on the trunk, either popcorn-shaped masses or streaming.
- Reddish-brown boring dust within the bark crevices or on the ground at the tree’s base.
- Signs of heavy woodpecker activity, such as flaked bark on the tree bole and flakes of bark on the ground below.
- Yellow to reddish-brown foliage throughout the entire tree crown.
Photo by: Kenneth E. Gibson, US Forest service, Bugwood.org
Some signs to look for:
- Shriveled, reddish brown damaged needles that soon fall
- Bare branch tips
- Thin crowns and topkill
- Defoliation from top down and outside in
- Grayish-brown forest when viewed from a distance
Photo by: Jerald E. Dewey, USDA Forest Service, Bugwood.org
Photo by: Jane Taylor, USDA Forest Service, Bugwood.org
For more information on root diseases:
The Rotten Truth (streaming video)
Stress from long-term drought conditions or from overstocking can weaken trees and make them susceptible to attack by other agents, such as bark beetles. Thinning forest stands will improve tree vigor and help trees cope with environmental stresses.
Heading using the h3tag
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