Field Guide to Diseases and Insect Pests of Idaho and Montana Forests

Susan K. Hagle – Plant Pathologist,
Scott Tunnock – Entomologist (retired),
Kenneth E. Gibson – Entomologist, and
Carma J. Gilligan – Biological Technician.

U.S. Department of Agriculture, Forest Service, State and Private Forestry, Northern Region, P.O. Box 7669, Missoula, Montana 59807. 1987. Reprint 1990. Publication Number R1-89-54.

I.  Key to the Common Diseases and Insect Pests of Idaho and Montana
    Conifers

A.  Stem and Roots
	1.  Conks, punk knots, and/or stem decay – 2
	1'.  Other symptoms or signs – 10
	a.  Stem Decay
		2.  Heartrot in western redcedar – 3
		2'.  Heartrot in other species – 5
	3.  Decay with small holes(pits), separates into sheets at the annual rings		Laminated Butt Rot
	3'.  Brown, red-brown, or yellow-brown decay with tendency for cubical cracking – 4
		4.  Decay confined to large and small pockets within heartwood; no conks	Brown Pocket Rot
		4'.  Decay involving a central cylinder of heartwood; conk, if present, brown,      gold with green or brown underside usually produced on ground	Schweinitzii Butt Rot
	5.  Brown to yellow-brown decay cracked into cubes or crumbly – 6
	5'.  Pitted or stringy, rot not cubical – 8
		6.  Dead trees and stumps only; heartwood and sapwood decayed; thin     mycelium felts sometimes present in cracks of decay; conk, usually     present, has CORKY CONSISTENCY, globular toshelving, cream-colored     lower surface, has small pores, upper surface, if present, gray to brown     with red band near margin	Redbelt Fungus
		6'.  Decay restricted to heartwood; live and dead trees decayed; conk not as      above – 7
	7.  Decay with large cubical cracks with thick white felts      of mycelium in cracks; conk large, chalky, white, columnar, usually present      on stem		Brown Heartrot
	7'.  Decay crumbles or powders when rubbed; cubical cracking usually evident,      occasionally with thin sheets of dry resin in cracks. Conk, occasionally found,      brown or gold with green or brown pored underside, usually produced on ground		Schweinitzii Butt Rot
		8.  In true firs, hemlock, occasionally spruce; yellow to orange or brown     stringy decay; conks with orange interior often present on bark	Indian Paint Fungus
		8'.  In all species; not as above – 9
	9.  Obvious white spots (pockets) with dark red or yellow-brown wood between;      pockets up to about one-half centimeter in diameter with bleached contents;      brown to gold conks on bark may be present; punk knots may be present		Pini Rot
	9'.  Decay in sapwood only and white or tan, spongy conk small (1-2 inches),      round, hollow with pink pore layer inside when fresh, hole in bottom when      mature		Pouch Fungus
	b.  Cankers and Miscellaneous Cambium Damaging Insects
		10.  On pines; swollen, resinous, or discolored areas of stem which may have        definite canker margins – 11
		10'.  Not as above – 14
	11.  Black stain under resinous patch of bark; lodgepole pine or ponderosa pine		Atropellis Canker
	11'.  Wood under bark not stained black – 12
		12.  On western white pine, whitebark pine, or limber pine	White Pine Blister Rust
		12'.  On lodgepole pine or ponderosa pine – 13
	13.  Globose swelling or canker flared broadly at edges		Western Gall Rust
	13'.  Swelling absent or not broad; in young stems, bark roughened, may be        slightly resinous, white to orange spores may be present; in older stems, oval        to oblong canker with barkiess center usually very resinous (often associated        with top kill in lodgepole pines)		Comandra Blister Rust, Stalactiform Blister Rust
		14.  True firs or Douglas-fir, sunken, discolored area on bark of sapling or        smaller tree; distinct line between live and dead cambium	Cytospora Canker
		14'.  On other species or not as described above – 15
	15.  On western larch; sunken discolored area on bark of sapling or smaller tree;        top of trees may be killed; distinct margin between live and dead cambium		Lachnellula Canker
	15'.  On other species or not as described above – 16
		16.  On true firs; bark covered with whitish spots of "waxy wool" from 1-2 mm        wide	Balsam Woolly Adelgid
		16'.  On other species or not as described above – 17
	c.  Bark Beetles and Wood Borers
	17.  Pitch tubes or masses of pitch on outside of bark – 18
	17'.  No pitch tubes or masses of pitch on bark. Orange, red, or whitish boring        'dust' in bark crevices. Pitch streamers (drips) sometimes present on bark        surface – 22
		18.  Under pitch mass, insect tunnel and, sometimes larvae within the outer        bark and phloem on Douglas-fir, ponderosa pine, and todgepole pine	Sequoia Pitch Moth
		18'.  Bark beetle gallery or adult beetles in tunnel (starting to build galleries)        under bark in cambium beneath pitch knot or mass – 19
	19.  On Engelmann spruce, boring 'dust', if present is red-brown; gallery pattern as        in figure 1E; larvae, if present, in groups		Spruce Beetle
	19'.  On ponderosa pine, lodgepole pine, western white pine, or whitebark pine – 20
		20.  On ponderosa pine or lodgepole pine; very large yellow-orange pitch        tubes generally restricted to lower 3 feet of stem. (See also Item 31 in        this key: Root Disease). Gallery as in figure 1H.	Red Turpentine Beetle
		20'.  Pitch tubes less than one-half inch in diameter, orange-red boring 'dust'        may be on bark; generally occurring above 3 feet on stem – 21
	21.  Ponderosa pine; gallery as in figure 1B. (See also Item 31 in this key: Root        Disease)		Western Pine Beetle
	21'.  In all pines; pitch tubes prominent; galler as in figure 1D		Mountain Pine Beetle
		22.  Pitch streamers or drips on bark surface at tree base or high on        stem – 23
		22'.  Pitch streamers not observed – 24
	23.  On Douglas-fir; pitch streamers high on stem with red-orange boring dust on        bark; galleries under bark as in figure 1F.		Douglas-Fir Beetle
	23'.  On any tree species; pitch flowing on outer bark near root collar up to 6 feet        on stem; under bark, white to cream-colored fans or felts of mycelium (often        throughout bark). (See also Item 31 in this key: Root Disease).		Armillaria Root Rot
		24.  Beetle entrance holes evident or red, orange or white boring dust on bark        surface or on ground around tree – 25
		24'.  Neither beetle entrance holes nor boring dust present – Root        Disease – 31
	25.  Boring dust on bark is white and powdery; under bark, "pinholes" surrounded        with brown or black stain go straight into sapwood		Ambrosia Beetles
	25'.  Boring dust on bark or ground orange or red – 26
		26.  On Engelmann spruce, boring dust dark red; bark flakes may be removed        from stem by woodpeckers; gallery pattern as in figure 1E.	Spruce Beetle
		26'.  On other tree species – 27
	27.  On pines – 28
	27'.  On Douglas-fir, true firs, or western larch – 29
		28.  Boring dust orange to red-brown; pitch tubes present; gallery patterns as        in figure 1D; tunnels packed with frass.	Mountain Pine Beetle
		28'.  Gallery pattern as in figure 1G; boring dust yellow-orange. (See also        Item 31 in this key: Root Disease).	Engraver Beetles
	29.  Douglas-fir or western larch; boring dust red-orange galleries as in figure 1F.        (See also Item 31 in this key: Root Disease).		Douglas-Fir Beetle
	29'.  On true firs; beetle entrance holes evident – 30
		30.  Mostly in grand fir; gallery pattern as in figure 1A. (See also Item 31 in        this key: Root Disease).	Fir Engraver Beetle
		30'.  Mostly in subalpine fir; gallery pattern as in figure 1C	Western Balsam Bark Beetle
	d.  Root Disease
	31.  Under bark of root collar or of roots, white or cream-colored mycelium fans or        felts, may also be found throughout bark, basal resinosus usually present		Armillaria Root Rot
	31'.  No mycelium fans or felts under bark – 32
		32.  On Douglas-fir, true firs, or western hemlock; cream-colored to rusty        brown mycelium on outside of root collar or root bark If decayed, root        sapwood or butt heartwood with pitted (small holes) decay that        separates easily into sheets at the annual rings	Laminated Root Rot
		32'.  Not as above – 33
	33.  Primarily on Douglas-fir, ponderosa pine, or lodgepole pine; in sapwood at root        collar or in roots, black stain in concentric crescents within annual rings		Black Stain Root Disease
	33'.  No black stain, or black stain not in concentric rings – 34
		34.  Sapwood of roots with white or yellow decay; brown or tan conks with        white underside (pore layer) found on surface of roots or within hollow        stump. Firm, small (2 ern or smaller), white mounds (button conks) on        bark of roots or root crown (especially of seedlings)	Annosus Root Rot
		34'.  Douglas-fir, seldom other species, center of roots with brown rot, or dark        red and heavily resinosus; roots sometimes have large galls with        decayed interior; conk, when present, brown to gold with green or brown        underside produced on ground near tree	Schweinitzii Root Rot

B.  Branch or Terminal
	1.  Witches broom formed – 2
	1'.  No witches broom – 5
		2.  Needles remaining green; on Douglas-fir, western larch, ponderosa pine, or      lodgepole pine	Dwarf Mistletoes
		2'.  Needles Yellow, tan, or brown; on true firs, spruce, or ponderosa pine – 3
	3.  On ponderosa pine		Elytroderma Needle Cast
	3'.  On true firs or spruce – 4
		4.  On true firs	Fir Broom Rust
		4'.  On spruce	Spruce Broom Rust
	5.  Soft-bodied, wingless insects often on succulent tissues of shoots, may also be      on foliage, stems, and roots; usually feed in groups; often associated with ants		Aphids
	5'.  Not as above – 6
		6.  On branches or terminals 1 or more years old – 7
		6'.  On current year's shoots – 12
	7.  Swelling on branch, nodes, or buds – 8
	7'.  No swelling, or only minor, not pronounced swelling, yellow to orange spores      sometimes present – 9
		8.  On ponderosa pine or lodgepole pine globose swelling, yellow to orange      spores may be present	Western Gall Rust
		8'.  On true firs only; outer branch nodes and terminal buds swollen, growth      stunted or stopped, red needles on dead branches, spots of white 'waxy      wool' on bark	Balsam Woolly Adelgid
	9.  On true firs, Douglas-fir, or spruce; branch dead, often with slight swelling      between dead and live tissue		Cytospora Canker
	9'.  On pines or western larch – 10
		10.  On larch; sunken, or discolored portion of bark or dead branch or        terminal tip; distinct line between live and dead cambium at margin of        sunken area	Lachnellula Canker
		10'.  On pines; somewhat swollen, roughened area on branch; yellow to        orange spores may be present – 11
	11.  On ponderosa or lodgepole pine		Cohmndra Blister Rust Stalactiform Blister Rust
	11'.  On western white pine, limber pine, or whitebark pine		White Pine Bliste Rust
		12.  On western larch – 13
		12'.  On spruce, ponderosa pine, or lodgepole pine – 14
	13.  Shoots wilted or withered, abundant hypodermelia needle blight evident in        stand		Hypoderm- ella Blight
	13'.  Shoots severed and abundant budworm defoliation (new needles webbed        and chewed) evident in stand		Western Spruce Budworm
		14.  Needles killed on tip only of new shoot of ponderosa pine or lodgepole        pine; needles not webbed; shoots wilted or crooked (curled down);        resinous lumps on bark on top of crook; red maggots sometimes        visible in pitch pockets under bark	Gouty Pitch Midge
		14'.  Entire new shoot killed or stunted – 15
	15.  On spruce or lodgepole pines 1-30 feet in height; mainly terminal shoots;        tunnels under bark of shoot and in wood		Terminal Weevils
	15'.  On ponderosa pine – 16
		16.  Tunnels in pith, packed with brown frass, terminal shoot usually        stunted. Terminal and lateral shoots can be killed; restricted to new        growth; usually in trees less than 15 feet tall	Western Pine Shoot Borer
		16'.  Lateral shoots killed, no tunnels in pith, dead needles on new and 1        year-old shoots	Diplodia Tip Blight

C.  Foliage
	1.  Damage on Douglas-fir, true firs, Engelmann spruce, or western hemlock – 2
	1'.  Damage on pines or larch – 15
		2.  Needles chewed: severed, chunks removed, stubs or midribs remaining      (defoliating insects) – 3
		2'.  Needles are not chewed but are discolored, spotted, or have mold on their      surface – 6
	3.  New needles chewed and webbed together to form ,nest' around larva; larvae      have brown heads, white spots on bodies		Western Spruce Budworm
	3'.  No webbing or sparse webbing – 4
		4.  Tussocks of hair on back of larvae; hairy cocoons sometimes visible on      foliage, limbs, or bark	Douglas-Fir Tussock Moth
		4'.  Larvae hairless – 5
	5.  On Douglas-fir only; larvae are a deep tan color and have a yellow, broad stripe      bordered by several darker strips on their underside; mainly in western Montana		Western False Hemlock Looper
	5'.  On most species of conifers, mainly in northern Idaho; larvae green to brown in      color with diamond-shaped markings on their backs		Western Hemlock Looper
		6.  Foliage covered with black or brown mold, matting needles together	Snow Mold
		6'.  Foliage without snow mold – 7
	7.  On Douglas-fir – 8
	7'.  On true firs or spruce – 11
		8.  Waxy white tufts	Cooley Spruce Gall Adelgid
		8'.  Spots, bands, or uniformly chlorotic; some needles may be shed – 9
	9.  Swelling on needles; orange maggots may be inside "gall"		Douglas-Fir Needle Midge
	9'.  No needle swelling – 10
		10.  Red or brown spots or bands	Rhabdocline Needle Cast
		10'.  Uniformly chlorotic or with tiny yellow fleeks. Tiny black spots emerging        from stomata on underside of needles	Swiss Needle Cast
	11.  Branches forming witches broom – 12
	11'.  No witches broom formed – 13
		12.  On true firs	Fir Broom Rust
		12'.  On spruce	Spruce Broom Rust
	13.  On spruce, waxy white tufts on needles or with yellow-purple galls on new        shoots		Cooley Spruce Gall Adelgid
	13'.  On true firs – 14
		14.  Needles discolored yellow, red, brown, or gray; or with black lines or        spots on underside; or with white to orange pustules protruding from the        undersides	Fir Needle Cast or Rust
		14'.  New shoot wilted, turning red from tip back, black fruiting bodies on        needles and new shoots	Delphinella Shoot Blight
	15.  On larch – 16
	15'.  On Pines – 22
		16.  Needles not chewed – 17
		16'.  Needles chewed – 19
	17.  Needles red or brown, drooping, remaining attached to spur; oblong black        spots may be present		Larch Needle Blight
	17'.  Needles yellow to brown in spots or bands especially toward tips – 18
		18.  Needles hollowed especially toward tips; dried straw-colored pieces of        needles (cases) may be sticking up on needle, hollowed needle tips        crooked or wilted	Larch Casebearer
		18'.  Needles not hollow or wilted, no casebearer	Larch Needle Cast
	19.  Webbed needles; needles pulled together in clusters forming tubes – 20
	19'.  No webbing or sparse webbing – 21
		20.  Nests tube-like and lined with silk; larvae have dark brown to black        heads and no white spots on body	Larch Bud Moth
		20'.  "Loose" webbed nest; larvae are light tan with white spots on body	Western Spruce Budworm
	21.  Chunks are eaten out of needles; larvae are gray-green with black shiny        heads		Larch Sawfly
	21'.  Needles partially eaten or cut off- larvae green to brown with diamond-shaped        markings on their backs		Western Hemlock Looper
		22.  Needles not chewed but are discolored, spotted, or have organisms on        surface – 23
		22'.  Needles chewed; severed, chunks removed, stubs or midribs remain        (defoliating insects) – 31
	23.  New shoots with white webbing, needles uniformly tan, stunted and easily        removed from sheath		Pine Needle Sheathminer
	23'.  White webbing absent – 24
		24.  Black or brown mold binding needles together in mass	Snow Mold
		24'.  Without black or brown mold – 25
	25.  On western white pine, whitebark pine or limber pine – 26
	25'.  On lodgepole pine or ponderosa pine – 27
		26.  Western white pine; I- and 2-year-old needles brown to gray; drooping on        branch	Dothistroma Needle Blight
		26'.  Whitebark or limber pine; I- and 2-year-old needles yellow, tan, red, or        grey; needles missing from branches	Lophoderm- ella Needle Cast
	27.  Needles with many white or black scales about 2 mm long – 28
	27'.  Needles without scales – 29
		28.  White scales	Pine Needle Scale
		28'.  Black scales	Black Pineleaf Scale
	29.  On ponderosa pine only; needles tan to yellow with red-brown transverse        bands		Dothistroma Needle Blight
	29'.  On ponderosa pine or lodgepole pine, needles tan to yellow or brown        especially toward tips – 30
		30.  On lodgepole pine; yellow to brown banded of progressing from tip	Lodgepole Pine Needle Cast
		30'.  On ponderosa pine; tan to brown needles - discoloration progressing        from tip; may be brooms, may be black lines of fruiting bodies at base of        needle	Elytroderma Needle Cast
	31.  Webbing nests		Sugar Pine Tortrix
	31'.  No webbing or sparse webbing – 32
		32.  Chunks removed randomly over needle or holes in needle; ponderosa        pine	Defoliating Weevil
		32'.  Large portions or entire needle consumed – 33
	33.  Looper (figure C) – 34
	33'.  Not looper (figure A or B) – 35
		34.  Mainly on ponderosa in eastern Montana; young larvae light brown with        yellow stripes; older larvae have tubercles and look like pine twigs	Pine Looper
		34'.  On white pines; larvae green to brown with diamond-shaped markings on        "backs"	Western Hemlock Looper
	35.  Larvae feed on all but current needles and are yellow-green with shiny black        heads; six or more pairs of "legs" on midportion of body as in (figure B)		Pine Sawfly
	35'.  Larvae are caterpillars as in (figure A); young larvae pale green with black        heads; older larvae have two white lateral stripes and green heads; older        foliage consumed; adults are white with black markings around edges of        wings		Pine Butterfly

D.  Seed and Cone
	1.  Damage WITHIN cones; boring dust, frass, or pitch evident on exterior of cone – 2
	1'.  Damage on EXTERIOR of cone; puncture holes present; may have pitch at      puncture – 3
		2.  Larva within cone has evident legs	Cone Worm
		2'.  Larva within cone is legless grub	Pine Cone Beetle
	3.  Adult or immature (nymph) true bug; body longer than wide; may be brightly      colored; hind leg flattened, adults strong fliers		Seed Bugs
	3'.  Not as described above. May be less important cone feeders or predaceous      insects not covered in this guide

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