Mountain pine beetle

What is mountain pine beetle?

Mountain pine beetle is a small bark beetle native to western North American forests. The Colorado State Forest Service notes it plays a natural role by killing diseased and dying pines, but in dense, drought-stressed forests during warm years it can explode into epidemics.

Beetles bore into the trunk and carry blue-stain fungi into the sapwood. A pine that is successfully attacked usually shows no change for months; then the whole crown turns yellowish to red, often 8 to 10 months later. Colorado State University says live beetles, eggs or larvae under the bark are the most certain sign.

For people in the East, the concern is moving firewood. Colorado State University says infested firewood can carry beetles to pines far from mountain forests, so don't bring pine firewood home from western trips.

Signs and damage

• Popcorn-shaped lumps of brown, pink or white resin (pitch tubes) on the trunk
• Boring dust in bark cracks and on the ground at the base
• Blue-gray stained sapwood
• Whole crown turning yellowish to reddish, usually 8 to 10 months after a successful attack

Mountain pine beetle identification: what to look for

• Adult: Small bark beetle about 1/8 to 1/3 inch long, with gradually curved rear wing covers (Ips beetles have sharp spines there).
• Signs: Pitch tubes (brown, pink or white), boring dust, blue-stained sapwood. A beetle stuck in a pitch tube can mean a failed attack.
• Damage: Crown turns yellowish to red, usually 8 to 10 months after a successful attack.
• Timing: In Colorado, adults fly mid-June through September, mostly late July (lodgepole) and mid-August (ponderosa).

Life cycle

One-year life cycle in Colorado. Larvae spend the winter under the bark and pupate in June and July. Adults emerge from mid-June through September, peaking in late July in lodgepole pine and mid-August in ponderosa pine, and attack new trees.

When to look: Flight is mid-June through September in Colorado. Fading crowns show 8 to 10 months after attack.

Mountain pine beetle look-alikes

A few things get mixed up with it:

• Ips engraver beetles: Also pine bark beetles, but the rear of the wing covers is sharply spined. Mountain pine beetle's is gradually curved.

How to control mountain pine beetle

Cultural control

• Thin dense, older stands to leave well-spaced, healthy trees, and keep a mix of tree ages.
• Treat infested logs before adults emerge in summer by peeling bark, burning or scorching, burying under at least 8 inches of soil, or chipping. Trees the beetles have already left need no treatment.
• The Colorado State Forest Service says the best practice is to remove an infested tree by the following spring, before beetles emerge, and not to move infested wood except to a secure drop-off site.
• Solar treatment works where the temperature under the bark reaches at least 110°F.
• Don't move pine firewood; see our firewood rules guide.

Chemical control

Colorado State University says preventive sprays can protect high-value green trees when applied each year between April 1 and July 1 (after June may be too late), with full coverage up and around the trunk; it names carbaryl, permethrin and bifenthrin. These sprays are preventive, for green trees that haven't been attacked; UC IPM says seriously infested trees can't be saved with insecticides and should be removed. The Colorado State Forest Service advises spraying only high-value trees and hiring a licensed pesticide applicator. Use only products labeled for this use; the label is the law. Tree spraying is a job for an ISA Certified Arborist or licensed applicator. Muthler Landscaping does not treat trees or apply pesticides; see our pesticide applicator license guide.

Use only products labeled for this pest and this site; the label is the law. For trees, work with an ISA Certified Arborist. If you hire someone to apply pesticides, make sure they hold your state’s pesticide applicator license; the rules for each state are in our pesticide applicator license guide.

Prevention

• Don't bring pine firewood back from western states.
• Keep pine stands thinned and healthy.

When to call a pro

In western states, call an ISA Certified Arborist or a state forester if high-value pines need preventive protection or show pitch tubes and fading crowns. In Pennsylvania, report any suspected western bark beetle find to DCNR's Division of Forest Health.

Related guides: Tree database: mature size and planting distance · Pennsylvania tree identification · Firewood rules by state · All pests and diseases

Questions about mountain pine beetle

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