The mountain pine beetle, a small insect that has killed millions of acres of pine trees in the western U.S. and portions of Canada, has shown up on trees in several western Nebraska communities.

Forest health experts with the Nebraska Forest Service said mountain pine beetle attacks have been reported in Scottsbluff, Gering, Minatare, Kimball, and areas of the Wildcat Hills.

Nebraska's first mountain pine beetle infestation was confirmed near Harrisburg this summer.

Mark Harrell, Nebraska Forest Service forest health program leader, said adult mountain pine beetles bore into pine trees from July through October, leaving small, marble-sized masses of resin, called pitch tubes, on the trunk.

"Adult beetles are black, about 1/4-inch long and lay eggs in the tunnels between the bark and wood," Harrell said. "Grub-like larvae hatch from the eggs and feed in the tree until July of the following year. The tunnels made by the larvae as they feed can kill a tree if enough larvae are present."

According to Harrell, Scotch pine is very susceptible to mountain pine beetle attacks, while Ponderosa and Austrian pines are susceptible to a lesser degree.

Trees heavily attacked by the mountain pine beetle have many pitch tubes on the trunk and usually die. To reduce the risk of the beetles spreading to nearby pines, these trees should be removed and either chipped, burned or moved at least 2 miles from other pines before the end of May.

Trees that are lightly attacked have only a few pitch tubes on the trunk and may not be killed by mountain pine beetle. These trees should be watched closely for any sign that the tree is dying and should be removed by the end of May if dying symptoms, such as yellowing needles, are seen in the spring.

Harrell said insecticide trunk sprays can be applied to prevent attacks on high-value trees and should be applied in the late spring but before mid-June.

"Carbaryl is the most effective insecticide for mountain pine beetle," said Harrell. "Bifenthrin and permethrin are also effective, but permethrin should be applied twice for better protection, first by mid-June and second by early August. Use only insecticides that have directions for mountain pine beetle on the label because similar products without mountain pine beetle on the label will not be as effective."

Harrell said insecticides will not control beetles that have already entered the tree.

Heavily attacked trees in forest stands also should be removed and either chipped, burned or moved at least 2 miles from other pines. Dense stands of trees are often stressed and more susceptible to attack. Thinning dense stands will improve tree health and will reduce the susceptibility of the trees to the beetle.

Improving tree health also will help pines in communities and residential landscapes to be less susceptible to the beetle. Timely supplemental watering can improve tree health during extended periods of drought. In average soils, trees can benefit from receiving 1 inch of water each week from rainfall or irrigation. During irrigation, however, water needs to drain from the soil before more water is applied.

The best way to water trees is to do it infrequently and let the water soak in deeply. Trees in soils with high levels of clay should receive not more than 1 inch per week, and those in soils with high levels of sand could use up to 2 inches of water each week. This is best if applied all at once or one half at a time. Daily or very frequent waterings can keep the soil too wet, or the soil may be moist on the surface but not moist enough a few inches below, depending on how much water is applied each time.

Harrell said mulching with wood chips or bark chips around the base of the tree, avoiding the use of weed killers around the tree and avoiding damage to the roots and trunk of the tree will also promote good tree health and reduce the susceptibility to the mountain pine beetle.

If you suspect a mountain pine beetle infestation or have questions about treating a tree or trees infested with mountain pine beetle, contact Harrell at (402) 472-6695.