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What’s bugging the forests: parasites, insects, fungus and more

| October 27, 2021 1:00 AM

BONNERS FERRY — If you look carefully, your trees are talking to you. Trees have marks and tell signs when they are sick.

Trees repair themselves when they have been damaged or are under stress. They use their sap as a barrier and where bark has been removed may turn red. Like humans they also fight fungal pathogens — Evergreens in particular when rooted in a moist environment.

According to the American Phytopathological Society some fungal pathogens can be life threatening to a tree, but they can adapt to many fungal pathogens overtime. Fungi can weaken a tree against other infections.

All trees make a pitch. Sometimes it forms in ball-like shapes. Survivalists have been known to use the pitch to keep fires going.

According to the Idaho Forest Products Commission, even the forests get sick — except when the trees get sick, it might just be because of a real bug.

Forest health problems also can be caused by parasitic plants and fungus infections, IDPC officials said on the group’s website. “Insects, fungi, and parasites are all natural parts of the forest ecosystem,” they note on the site. “And just like the bacteria in our bodies, they only become a problem when something gets out of whack.”

Those bugs can include everything from bark beetles, defoliators, dwarf mistletoe and root diseases.

Bark beetles

Bark beetles cause a lot of visible damage to the trees in the Idaho forest, IFPC officials said. Trees weakened by old age, drought, overcrowding, disease, or weather can make them vulnerable to bark beetles. The beetles bore through the bark to access 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 because it will be unable to send nutrients up and down the trunk, commission officials note.

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, IFPC officials said on the website. “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,” they said.

The most common defoliators found in the state’s forests 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, IFPC officials said.

Dwarf mistletoes

These clumpy, parasitic growths rob nutrients from the host tree, IFPC officials said of its inclusion on the list. “By robbing nutrients, dwarf mistletoes impair the tree’s ability to grow,” officials said. “Trees that are heavily infected by dwarf mistletoes can be permanently stunted and can die.”

Root diseases

Root diseases are the “hidden killers” of Idaho’s forests, because they attack the underground roots of trees, commission officials said. When a tree is healthy, its natural defenses prevent infection by naturally occurring fungi found in the soil. However, when a tree is weak or damaged, the fungi can attack the roots, and can quickly move up the tree causing extensive damage.