You probably don't even think about it, but our forests get sick, too. But when the forest catches a "bug," it just might be a real bug!
Forest health problems also can be caused by parasitic plants and fungus infections. Insects, fungi, and parasites are all natural parts of the forest ecosystem. And just like the bacteria in our bodies, they only become a problem when something gets out of whack.

Some of the things that bug the Idaho forest are: Bark Beetles, Defoliators, Dwarf Mistletoes, and Root Diseases.

Bark Beetles

Bark beetles cause a lot of visible damage to the trees in the Idaho forest. They attack trees that are weakened by old age, drought, overcrowding, root disease, or weather damage. Bark beetles bore through the bark to eat the tasty nutrients in the inner bark ("phloem") and "cambium" layers. If they eat all the way around the tree, (called "girdling" the tree) the tree will die -- its food tube will have been cut and it will be unable to send nutrients up and down the trunk.

Idaho's bark beetle population includes the western pine beetle, mountain pine beetle, Douglas-fir beetle, and fir engraver.


Defoliators hurt trees by eating the green needles that take in carbon dioxide and release oxygen into the atmosphere. Damage to the needles impairs the tree's ability to "breathe" and to collect sunlight for manufacturing sugars, weakening it and making it more vulnerable to damage from other pests and diseases.

In Idaho's forests, most defoliators are moths, such as the Douglas-fir tussock moth and the western spruce budworm. The tussock moth has caused significant damage to the forest in recent years, affecting 15% of the forested area of the Boise National Forest.

Dwarf Mistletoes

These clumpy, parasitic growths rob nutrients from the host tree. By robbing nutrients, dwarf mistletoes impair the tree's ability to grow. Trees that are heavily infected by dwarf mistletoes can be permanently stunted and can die. Because of their scraggly looks, tree branches that have been infected with dwarf mistletoe are sometimes called "Witch's Brooms."

Root Diseases

Root diseases are the "hidden killers" of Idaho's forests, because they attack the underground roots of trees. Root diseases are caused by fungi that live in the soil. When a tree is healthy, its natural defenses prevent infection by these naturally occurring fungi. But when a tree is weak, damaged, or otherwise diseased, the fungi can attack the roots, and can quickly move up the tree causing a great deal of damage.

In Idaho's forests, root diseases include laminated, black stain, annosus, and armillaria -- the most widespread of all root diseases in the northwest.

More Information:


Idaho Forest Products Commission
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