Tree Symptom Decoder



Apple


Powdery Mildew: White powder-like substance on the upper and lower areas of the leaf

Chlorosis: Pale green to yellowish leaves

Fire Blight: Light brown to black leaves; dried fruit; water logged blossoms; dead 'shephards crook' twigs and branches
 

Ash


Leafcurl Ash Aphid: Leaves tightly rolled and thickened; white/waxy insects may be evident

Lilac/Ash Borer: Exit holes the size of a pencil eraser; usually found along branch crotches, branches, or the main stem; die-back may be evident

Ash Flower Gall Mite: Infested flowers become deformed and remain on trees as green masses until fall

Ash Twig Borer: Exit holes the size of a pencil led tip; usually found along smaller twigs

Aspen


Shoot Blight: Irregular brown/black spots form on leaf; infected shoots turn black and resemble a 'shephards crook'

Leaf Spots: Tan to black spots that develop on the leaf surface

Aphids: Leaf curling, presence of ants or a sticky honeydew-like substance on the leaf

Powdery Mildew: White powder-like substance on the upper and lower areas of the leaf

Chlorosis: Pale green to yellowish leaves

Poplar Twiggall Fly: Presence of smooth, knot-like gall on tip of aspen twig; Cytospora Canker may develop around the gall

Oystershell Scale: A cluster of grey scales resembling rice along the bark and branches; sometimes settling near buds

Cytospora Canker: Orange oozing spores form along the main stems; girdling occurs on section of tree above the canker

Bacterial Wetwood: Oozing liquid from wounds; yellow-brown discoloration of bark

Birch


Bronze Birch Borer: Bronze colored insect borer; D-shaped exit holes along main stem and branches; Dieback of terminal branches

Black Locust


Locust Borer: Insect is an inch long and very colorful (black body, yellow stripes, red legs); Dieback and knotty swelling may be evident

Boxelder


Aphids: Insects sucking on leaf surface, sticky leaf surface, flying insects around the canopy

Boxelder Bugs: Black 1/2" insects with red lines on thorax, orange/red eggs in clusters on leaf surface, usually found surrounding homes near south-facing windows

Buckeye


Leaf Scorch: Burn appearance along margin of the leaf; can resemble leaf spots

Catalpa


Verticillium Wilt: Rapid dieback or wilting of individual branches on tree; usually not the entire tree

Cherry


Peach Tree Borer: Presence of a wet spot or oozing, gummy sap along lower trunk

Cytospora Canker: Orange oozing spores form along the main stems; girdling occurs on section of tree above the canker

Aphids: Leaf curling, presence of ants or a sticky honeydew-like substance on the leaf

Chokecherry


Black Knot Disease: Black, swollen growths form along the branches and stems; galls may be covered with olive-green spores

Fall Webworm: White webbing present in the branches and crown of the tree

Cottonwood


Cytospora Canker: Orange oozing spores form along the main stems; girdling occurs on section of tree above the canker

Shoot Blight: Irregular brown/black spots form on leaf; infected shoots turn black and resemble a 'shephards crook'

Leaf Spots: Tan to black spots that develop on the leaf surface

Powdery Mildew: White powder-like substance on the upper and lower areas of the leaf

Petiole-Gall Aphid: Swelling/thickening of the petiole which results in the formation of round galls

Bacterial Wetwood: Oozing liquid from wounds; yellow-brown discoloration of bark

Crabapple


Powdery Mildew: White powder-like substance on the upper and lower areas of the leaf

Fire Blight: Light brown to black leaves; dried fruit; water logged blossoms; dead 'shephards crook' twigs and branches

Chlorosis: Pale green to yellowish leaves

Elm


Elm Leaf Beetle: Leaves are skeletonized; holes throughout leaves

Elm Leaf Miner: Tunnels made throughout the leaf surface

European Elm Scale: Scales group together on crotch of branches; scales are dark-red, purple, or brown surrounded by white wax fringe

Squirrel Damage: Squirrels tend to chew on buds and tree bark during winter months; may cause girdling around wounds

Bacterial Wetwood: Oozing liquid from wounds; yellow-brown discoloration of bark

Hackberry


Hackberry Nipplegall: Leaves with large, raised bumps

Eriophyid Mites: Branches/twigs deformed into a dense mass called "Witches Broom"

Hawthorn


Fire Blight: Light brown to black leaves; dried fruit; water logged blossoms; dead 'shephards crook' twigs and branches

Chlorosis: Pale green to yellowish leaves

Pear Slug: Chewing/holes in leaves

Rusts: Orange/yellow spots on leaf surfaces

Honeylocust


Honeylocust Plant Bug: Dieback/twisted leaves; usually occurs on new growth

Honeylocust Podgall Midge: Leaflets swell to form galls; When maggots emerge, galls drop leaving bare branches

Honeylocust Leafhopper: Spotty yellow foliage; can occur alongside Plant Bug infestation in late spring

Honeylocust Spidermite: Orange 1 mm mites usually found under bud scales/in bark cracks; Bronze dieback within foliage

Thyronectria Canker: Rust to Black colored fruiting bodies along dead areas of bark; Premature leaf drop

Juniper


Cedar Apple Rust: Large galls develop on ends of branches; orange telial thorns form during rainy weather; dieback throughout tree

Juniper Spittlebug: White, frothy masses develop on needles

Spider Mites: Speckled leaf surface; plant appearance becomes bronze/gray; leaf scorch

Linden


Leaf Scorch: Leaf spots; burn along margin of the leaf

Maple


Chlorosis: Pale green to yellowish leaves

Aphids: Leaf curling, presence of ants or a sticky honeydew-like substance on the leaf

Winter Sunscald: Sunken/discolored bark; cracked or sloughed off bark

Mountain Ash


Fire Blight: Light brown to black leaves; dried fruit; water logged blossoms; dead 'shephards crook' twigs and branches

Oak


Bullet Gall: Woody, round gall on branches

Squirrel Damage: Squirrels tend to chew on buds and tree bark during winter months; may cause girdling around wounds

Chlorosis: Pale green to yellowish leaves

Pine


Ips Beetle: Tunnels underneath bark; severe dieback present

Diplodia Blight: Needle kill at tips of branches; needles yellow/brown in color

Dothistroma Blight: Needle drop/browning of needles; bare branches

Mountain Pine Beetle: Popcorn-like "pitch tubes" of resin along main trunk; flakes of bark lie on ground below tree canopy; yellow/red foliage

Spruce


Spider Mites: Speckled leaf surface; plant appearance becomes bronze/gray; leaf scorch

Cytospora Canker: Orange oozing spores form along the main stems; girdling occurs on section of tree above the canker

Rhizosphaera Needle Cast: Loss of needles on innermost branches towards the bottom of the spruce; black spots on surface of needle

Walnut


Thousand Cankers Disease: *** Not yet in Wyoming ***

Willow


Bacterial Wetwood: Oozing liquid from wounds; yellow-brown discoloration of bark

Cytospora Canker: Orange oozing spores form along the main stems; girdling occurs on section of tree above the canker