Tree Symptom Decoder

To use the Tree Symptom Decoder:

1) Correctly identify your tree (to the general type - genus if possible).

2) Click on the tree name in the content list to the right.

3) Look through the list of general signs and symptoms for the best description of the health issues for guidance from reputable resources.

*This is not an exhaustive list of pest and disease issues.

Hint: Make sure to correctly identify your tree! Some trees are cultivated for specific genetic traits that display aesthetically pleasing or desirable physical appearances from the typical or straight species. This is known as a "cultivar" or [culti]vated [var]iety.

Remember it is always best to get a professional opinion from a certified or licensed professional before applying any chemicals or performing any large mechanical treatments that could potentially lead to injury or safety issues. Check out our Find Professional Tree Care Services page for more information on finding local professional services.

Apple (Malus)

Chlorosis: Pale green to yellowish leaves

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

Japanese Beetle: Brown to bronze and metallic green beetle with six white tufts of hair along hind sides of abdomen.

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

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

Ash (Fraxinus)

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

Emerald Ash Borer: Adult is 1/2 inch long, narrow, metallic green beetle, D shaped exit hole (1/8" diameter) found on trunk or branches *this insect has not been officially detected in Wyoming*

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

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

Wood Boring Insects of Ash Trees: Major and minor wood boring insects of ash trees.


Aspen (Populus)

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

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

Chlorosis: Pale green to yellowish leaves

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

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

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

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

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

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


Birch (Betula)

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

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


Black Locust (Robinia)

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


Boxelder (Acer negundo)

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/Horsechestnut (Aesculus)

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


Catalpa (Catalpa)

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


Cherry (Prunus)

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

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

Japanese Beetle: Brown to bronze and metallic green beetle with six white tufts of hair along hind sides of abdomen.

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


Chokecherry (Prunus)

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

Eastern Tent Caterpillar: White webbing present is thickly constructed in the forks and crotches of trees; the larvae do not feed within their webs, but congregate there at night and during rainy weather.

Eriophyid Mites: Leaves have finger-like protrusions growing on surface.

Fall Webworm: White webbing present in the branches and crown of the tree, and occur in summer and fall, whereas eastern tent caterpillars appear in spring.


Cottonwood/Poplar (Populus)

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

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

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

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

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

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


Crabapple (Malus)

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

Chlorosis: Pale green to yellowish leaves

Japanese Beetle: Brown to bronze and metallic green beetle with six white tufts of hair along hind sides of abdomen.

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

Elm (Ulmus)

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

Elm Leaf Beetle: Leaves are skeletonized; holes throughout leaves

Elm Leafminer: 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

Japanese Beetle: Brown to bronze and metallic green beetle with six white tufts of hair along hind sides of abdomen.

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

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


Hackberry (Celtis)

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

Hackberry Nipplegall: Leaves with large, raised bumps


Hawthorn (Crataegus)

Chlorosis: Pale green to yellowish leaves

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

Pear Slug: Chewing/holes in leaves

Rusts: Orange/yellow spots on leaf surfaces


Honeylocust (Gleditsia)

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

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 Spider Mite: 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 (Juniperus)

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/Basswood (Tilia)

Japanese Beetle: Brown to bronze and metallic green beetle with six white tufts of hair along hind sides of abdomen. Primarily littleleaf lindens are of concern.

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

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


Maple (Acer)

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

Chlorosis: Pale green to yellowish leaves

Eriophyid Mites: Leaves display masses of pinkish patches

Japanese Beetle: Brown to bronze and metallic green beetle with six white tufts of hair along hind sides of abdomen.

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


Mountainash (Sorbus)

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

Japanese Beetle: Brown to bronze and metallic green beetle with six white tufts of hair along hind sides of abdomen.

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


Oak (Quercus)

Bullet Gall: Woody, round gall on branches

Chlorosis: Pale green to yellowish leaves

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


Pine (Pinus)

Chlorosis: Pale green to yellowish needles

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

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

Ips Beetle: Tunnels underneath bark; severe dieback present

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

Pine Wilt Disease/Nematode: Primarily seen in exotic species, quick fading of color in leaves/needles within a few weeks to a couple of months leading to mortality of the tree.


Spruce (Picea)

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

Ips Beetle: Tunnels underneath bark; severe dieback present typically from the top of the tree downward.

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

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


Walnut (Juglans)

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


Willow (Salix)

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