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Epidemic of spruce bark beetles means higher risk of fire danger

Posted: Saturday, March 04, 2000

The ever-present spruce bark beetle has undergone a major population surge on the Kenai Peninsula, especially throughout the southern part.

"They're always in the woods around us," said Janice Chumley, an integrated pest manager with the University of Alaska Fair-banks cooperative extension office in Soldotna.

"They're in your front yard now."

The beetles are reproducing faster and in greater numbers than at any other point since records began in the late 1800s.

Many beetle watchers -- foresters, entomologists and firefighters -- attribute the beetle baby boom to low rainfall and average summer temperatures nearly three degrees higher than normal.

Chumley said the beetles are part of a recurring cycle of birth, death and regeneration in the peninsula's forests.

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"It's part of a natural cycle to make sure trees don't get too large or too old," she said.

Although the beetles may be good news for the forests, they aren't for the people who live around them.

Spruce bark beetles infest -- as their name suggests -- the bark of spruce trees indigenous to the peninsula. Boring through the bark and into the soft vascular tissue just beneath, called cambium, females build large hollows to lay eggs, while males simply live in the sections they've eaten.

As the beetles burrow into the cambium, these tunnels and hollows prevent the trees from getting nutrients from the soil to the needles where it is converted to food.

In this fashion, spruce bark beetles effectively starve their host trees to death.

Trees killed by infestation are far drier and less stable than those that die a natural death.

Central Emergency Ser-vices fire chief Len Malm-quist said beetle-killed trees are a tremendous fire hazard.

"They burn much hotter and much faster," he said. "Because there is no moisture, it's going to burn hotter."

The best way to protect against a beetle infestation is to make sure trees are healthy by watering and fertilizing them, according to Jeff Graham, the state Division of Forestry's forest stewardship coordinator.

"A healthy, vigorous tree will produce more pitch. A tree uses pitch to force (insects) out," Graham said.

Another way to make a tree less attractive to predators is to avoid pruning before June, he said.

Young bark beetles leave the trees where they were born and fly off to find new hosts between the middle and end of May. Freshly pruned trees leak resin, which attracts beetles in flight, Graham said.

While insecticides are a viable option, Graham recommends they only be used on larger, older trees, which are more likely to be attacked, and only on a few.

"It's not recommended for more than a dozen or so trees, because of cost," he said.

In order to reduce fire risk, infested trees should be removed and healthy trees protected.

The first step is determining which trees beetles have already preyed upon.

If needles are green, and a dusty rust-colored pitch does not appear in bark crevices from eye level to the ground, the tree has not been attacked.

If needles are green, and a rusty brown dust appears at ground to eye level on bark, in bark crevices or on the ground, the tree has been attacked during the current season. Also, woodpecker activity may confirm an infestation.

If needles are a faded yellow, orange or red, and brown dust is present, the tree was attacked last season. At this stage beetle larvae, pupae and adults are present under the bark.

If twigs and limbs are bare of needles and bark appears reddish brown in overall color, the tree was attacked two to three seasons earlier. Further evidence would be bore holes in the bark with rust-colored dust. Some adult beetles may remain under bark.

If no needles or twigs remain on branches and the tree appears silver-gray in color, it was attacked three or more seasons prior. Remaining bark will be loose and beetle activity will be evident underneath. No spruce beetles will be present.

For healthy trees:

Once a spruce tree has been identified as healthy, there are ways to protect it from beetle attack.

Fertilize and water each tree early in the growing season and throughout the summer. Fertilizers high in phosphorous may help a tree's production of roots, which in turn helps it reach more water and nutrients. Trees should be given a pound of fertilizer for each inch of trunk circumference. Apply fertilizer to roots or drip zones -- the ground over which the tree's branches extend. Water very well.

Special insecticides have been registered for use against spruce beetles. These are carbaryl and lindane. Spray spruce trees before the end of May in order to protect them during the beetles' emergence and dispersal flight.

Thinning trees from crowded lots reduces competition and encourages vigorous growth.

For infested trees:

Once a spruce tree has been identified as infested, it should be removed from the area before the middle of May. Debark and split wood immediately for firewood to help it dry and to expose the cambium and phloem tissues in which the beetles live. Cut the trees as close to the ground as possible to get rid of the greatest number of beetles.

Both the integrated pest management scouts and forest stewards are available to help identify and deal with infestations. They can be contacted at the cooperative extension office, 262-5824, or the Alaska Division of Forestry, 262-4124.



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