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    • Insects and diseases are a natural part of forest ecology. They can become pests during outbreaks or when they interfere with management goals, such as timber production, wildlife habitat, water quality, recreation and views. 

    Identification Resources

    Western Montana Forest Insects & Diseases: A Guide to Identification and Mitigation covers common insects and diseases in western Montana. 

    Field Guide to the Diseases and Insect Pests of Northern and Central Rocky Mountain Conifers is a useful resource for identifying insects and diseases.

    USDA Forest Service Forest Insect and Disease Leaflets offer in-depth information on nearly any insect or disease you might encounter.

    Common Insects and Diseases

    Small black oval scale insects with raised centers on pine needles. Slight yellow halo around scale insects where feeding has occurred.

    Black Pineleaf Scale

    Diplodia fruiting bodies on pine cone. Fruiting bodies are small, swollen blue-black sacs.
    Diplodia Shoot and Tip Blight
    Douglas-fir beetle galleries. Main galleries are long and straight, with smaller larval feeding galleries on alternate sides.

    Douglas-fir Beetle

    Douglas-fir Tussock Moth Larvae. This caterpillar is covered in yellow-white hairs, has four yellow-orange tufts of hair on its back segments, has red dots and a large orange and black tuft of hair at its head.
    Douglas-fir Tussock Moth
    Dwarf mistletoe-infected trees in a wildflower meadow. Dwarf mistletoe brooms are round and bushy, with infected tees showing topkill (dead tree tops).
    Dwarf Mistletoe
    Elytroderma broom in lower pine tree canopy. Broom consists of clumpy red needles.
    Elytroderma
    Fir engraver galleries are horizontal along trunk of grand fir. Smaller larval galleries extend vertically from main horizontal gallery.
    Fir Engraver
    Lodgepole pine trunk covered with yellow, popcorn-shaped pitch tubes formed as a defense response by the tree against mountain pine beetle attack.
    Mountain Pine Beetle
    Dead tan-colored larch needles with small black irregular fruiting bodies, characteristic of larch needle blight, surrounded by healthy green live needles
    Needle Diseases
    Green and white pheromone bubble capsule stapled to trunk of Douglas-fir tree.
    Pheromones for Bark Beetles
    Ips pine engraver galleries are X and Y shaped.
    Pine Engraver (Ips)
    Red turpentine beetle stuck in red pitch tube where tree has pushed the beetle out with resin.
    Red Turpentine Beetle
    Fallen tree with suspected Heterobasidion root disease. Roots and base of tree are decaying and breaking apart.
    Root Diseases
    Sporulating western gall rust. Gall is a round swelling on branch, with red dead bark and orange rust spores.
    Western Gall Rust
    Western pine beetle galleries are circuitous, some adult beetles are present.
    Western Pine Beetle
    Western spruce budworm pupal case hanging from twig. Pupal case is striped bronze and black, with white webbing holding onto twig.
    Western Spruce Budworm
    Western sculptured pine borer, a type of flat-headed wood borer. Grey, bullet shaped body with short antennae and shiny black and silver markings.
    Wood Borers