Colorado's Common Insects and Diseases

Mountain Pine Beetle . Ips Beetle . Dwarf Mistletoe . Aspen Insects & Diseases
Spruce Bark Beetle . Western Spruce Budworm . Insect & Disease Publications

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Check out USDA Forest Service's Forest Insect & Disease Aerial Survey of the Rocky Mountain Region

Colorado's Primary Forest Insects and Diseases in 2007

Click on the map for a larger PDF (8.1 MB PDF)

Mountain Pine Beetle

Mountain pine Beetle (MPB) is an insect native to the forests of western North America and is also known as the Black Hills beetle or the Rocky Mountain pine beetle. MBP primarily develop in pines such as ponderosa, lodgepole, Scotch & limber pines, and less commonly affect bristlecone and piñon pines. These outbreaks can be devastating and have resulted in the loss of millions of trees.

Colorado Mountain Pine Beetle Infestation Map for All Species (as of 2007)

Right: MPB infestation map showing all species 1996-2007 Click on the map for a larger version (13 MB PDF)

Symptoms of Infestation

Popcorn-shaped masses of resin, called “pitch-tubes,” (which may be brown, pink, or white in color) will be found on the trunk where the beetle began tunneling. Boring dust may be found in bark crevices or on the ground immediately adjacent to the tree base. Evidence of woodpeckers feeding on the trunk may indicate MPB infestation. Patches of bark may be missing where the woodpecker was feeding, and bark flakes found on the ground below the tree. These symptoms are very similar to the ips beetle; be sure to properly identify the beetles you find associated with your tree.

Management Options

Logs infested with MPB larvae can be treated in various ways to kill developing beetles before they emerge as adults in summer. Treatments include:

1. Burning, burying, or removing infested logs.
2. Chemically treating logs with “borer spray.” (Always carefully read and follow all label precautions before applying insecticides.)
3. Solar treatments.

Want to learn more about MPB? Please check out the following documents:

Bark Beetles. Are Your Trees At Risk? (2.4 MB PDF)
Mountain Pine Beetle (281 KB PDF)
Mountain Pine Beetle Poster (313 KB PDF)
Mountain Pine Beetle Management Poster (1.3 MB PDF)
Solar Treatment of Mountain Pine Beetle Trees (14 KB PDF)
Preventive Spraying for Mountian Pine Beetle (17 KB PDF)
Pages 3 through 12 of the 2005 Report on the Health of Colorado's Forests (7.52 MB PDF)

This section didn't quite descibe your tree's ailments? Check out our Sick Tree ID Guide to find out what's actually wrong.

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Ips Beetle

Ips beetles, sometimes known as “engraver beetles,” are bark beetles that develop under the bark and tunnel through the tree, damaging and killing pine and spruce trees. Two factors that contribute to ips beetle problems in Colorado include prolonged drought stress and the creation of freshly-cut wood (preferred breeding site). Ips beetles are 1/8 to 3/8 inch long and reddish brown to black. They are similar in appearance to the mountain pine beetle and it is important to correctly identify the species in order to prescribe an effective management strategy.

Symptoms of Infestation

Mature ips beetles enter trees and tunnel, producing a yellowish- or reddish-brown boring dust. This accumulates in bark crevices or around the base of the tree and effected parts of the tree discolor and die. Small round holes in the bark of infested trees indicate the beetles have completed development in that part of the tree and have exited. The presence of woodpeckers, a common predator of the ips beetles, may indicate infestation. These symptoms are very similar to mountain pine beetle; be sure to properly identify the beetles you find associated with your tree.

1. To prevent attacks, use practices that promote vigorous tree growth. Maintain health and ensure adequate water supply.
2. Remove all freshly cut materials that result from pruning or thinning trees, as these attract ips beetles.
3. Do not stack infested wood next to living trees.
4. Insecticides can be used to prevent infestations, but must be applied prior to an attack. (Always carefully read and follow all label precautions before applying insecticides.)

Want to learn more about Ips Beetle? Please check out the following documents:

Ips Beetles (298 KB PDF)
Ips Beetle Poster (946 KB PDF)
Pages 3 through 12 of the 2005 Report on the Health of Colorado's Forests (7.52 MB PDF)

This section didn't quite descibe your tree's ailments? Check out our Sick Tree ID Guide to find out what's actually wrong.

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Dwarf Mistletoe

Dwarf mistletoe, a common problem in Colorado Forests, predominantly affects ponderosa and lodgepole pines, although they can attack Douglas-fir, piñon and limber pines. Dwarf mistletoes are small, leafless, parasitic, flowering plants which kill by slowly robbing the tree of food and water. Damages include growth reduction, loss of wood quality, poor tree form, predisposition to insect infestation and diseases, premature death, and reduction in seed crops.

Symptoms of Infestation

The first symptom of dwarf mistletoe infection is a slight swelling of the bark at the infection site. The parasite is identifiable when the yellow to green or brownish-green segmented shoots protrude from the infected part of the tree, which form about 2-3 years after the infection. Because dwarf mistletoes are slow killers, long-term management options are feasible.

Management Options

1. Pruning and removing infected trees is the best management measure available to reduce or eliminate dwarf mistletoe infestations.
2. Plant resistant trees under infected ones to replenish forest after infected ones are removed.
3. If planting same species as infected tree, use approved sprays to reduce the risk of infestation. (Always carefully read and follow all label precautions before applying insecticides.)

Want to learn more about dwarf mistletoe? Please check out the following documents:

Dwarf Mistletoe Management (127 KB PDF)
Dwarf Mistletoe Poster (232 KB PDF)
Pages 3 through 12 of the 2005 Report on the Health of Colorado's Forests (7.52 MB PDF)

This section didn't quite descibe your tree's ailments? Check out our Sick Tree ID Guide to find out what's actually wrong.

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Common Insects and Diseases of Aspen

Aphids
Aphids are small insects that feed by sucking plant sap from leaves and excrete a sweet sticky substance called honeydew. The damage is mostly unsightly but, in the long-term, may kill the branches they feed on.
Aphids on Shade Trees and Ornamentals Fact Sheet (43 KB PDF)

Ink Spot Disease
Ink spots are a result of the fungus Ciborinia and are commonly found in dense aspen stands. This disease causes leaf discoloration and early leaf drop which may reduce tree growth.
Aspen and Poplar Leaf Spots Fact Sheet (203 KB PDF)

Marssonina Blight
The Marssonina fungus causes this most common disease on aspen foliage. Although there is leaf discoloration, this condition usually is not damaging. Heavy infestations cause early leaf drop.
Aspen and Poplar Leaf Spots Fact Sheet (203 KB PDF)

Aspen Leaf Miners
Adult leaf miners cut tiny slits on aspen leaves and lay their eggs inside. The larvae live inside the leaf and feed by “mining” chlorophyll from plant cells; this is not harmful to the tree's health.
Leaf Miners Fact Sheet (128 KB PDF)

Sawflies
Sawflies are closely related to wasps. The larvae are plant feeders and look like hairless caterpillars. Sawflies often feed in groups and can quickly defoliate portions of their host plant.

Elk Scarring
Elk browse on the shoots and stems of aspen trees, creating wounds which allows for the introduction of diseases.

Western Tent Caterpillar
This defoliating caterpillar feeds on the leaves of aspen, causing aesthetic damage. Consecutive years of defoliation, however, may kill the tree.
Tent Catepillar Fact Sheet (88 KB PDF)

Oystershell Scale
Scale, a common and destructive pest, overwinter on trees and harm them by sucking sap. Branch and tree death are possible with long-running infestation.
Oystershell Fact Sheet (78 KB PDF)

Poplar Twiggall Fly
These common galls are caused by tiny black flies. While they will continue to grow years after they are produced, they do not threaten the health of the tree.
Poplar Twiggall Fly Fact Sheet (144 KB PDF)

Blank Canker
This slowly developing canker is caused by the fungus Ceratocystis fimbriata and is easily recognized. The canker rarely kills the tree due to its slow development.

Sooty Bark Canker
Sooty bark canker is caused by the fungus Encoelia pruinosa and is the most lethal canker on aspen in Colorado. The dead bark falls off and exposes the crumbly black, sooty inner bark.

Epidermal Bark-Mining Fly
This curious spider-shaped track is made by the larvae of a fly and is not harmful to the health of the tree.

Trunk Rot
Phellinus igniarius decay fungus enters through old branch stubs or other wounds. Affected trees often are used by hole-nesting birds.

Poplar Borer
This wood-boring beetle lays eggs on the bark of the aspen. The larvae then tunnel, weakening the wood. Entry and exit holes of the beetle invite fungi, which can result in limb breakage.
Shade Tree Borers Fact Sheet (244 KB PDF)

Keeping Your Aspen Healthy

•   Maintain a proper watering schedule – aspen will suffer if over- or under-watered.
•   Prevent direct sprinkling of leaves by lawn watering systems.
•   Unwanted aspen sprouts that appear in the lawn may be mowed. DO NOT spray the
    sprouts; these are connected to the mother tree.
•   Avoid wounding the main trunk with movers or weed wackers.
•   Trim out cankers that are less than half the circumference of the aspen.
•   Clean up heavy scale insect infestations.

What's Wrong With Your Aspen? Poster (935 KB PDF)
Pages 13 through 19 of the 2005 Report on the Health of Colorado's Forests (7.52 MB PDF)
Aspen and Poplar Leaf Spots (203 KB PDF)

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Spruce Bark Beetle

The spruce bark beetle has caused extensive tree damage to all species of spruce throughout the West. These infestations are usually found in large diameter trees that have been felled by wind or stressed by natural factors such as flooding, drought, or old age.

Symptoms of Infestation

Needles on infested trees tend to drop to the ground after high winds. This can happen the second summer after the tree has been infested. On other trees, the needles fade to an orange-red. Trees that have been killed by the spruce bark beetle are very dry and may create a severe fire hazard. Wood products can be lost and watershed function impaired.

Management Options

Large outbreaks of the spruce bark beetle are very difficult to control. Small infestations can be eliminated by quick action such as removal of infested trees. Contact a professional forester about the silvicultural, physical, and chemical management practices available.

Want to learn more about spruce bark beetle? Please check out the following document:

Spruce Bark Beetle Poster (270 KB PDF)
Pages 3 through 12 of the 2005 Report on the Health of Colorado's Forests (7.52 MB PDF)

This section didn't quite descibe your tree's ailments? Check out our Sick Tree ID Guide to find out what's actually wrong.

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Western Spruce Budworm

Western spruce budworm is the most widely distributed forest defoliator in western North America. The budworms have a one-year life cycle and are actually a small moth at full maturity. Here in the west there can be severe infestations in healthy Douglas-fir, white fir, and spruce.

Symptoms of Infestation

Evidence of western spruce budworm can be observed all year-round. Dead branches or sparse foliage may indicate feeding during previous years. Budworms have the potential to consume all new growth on the host tree. During outbreaks of three or more successive years, trees may die. Budworms create ideal conditions for other insect and disease invasions.

Management Options

1. Budworm populations can be substantially reduced with chemical insecticides. Large forested areas can be aerially sprayed for short-term protection and individual trees can be sprayed using ground equipment. (Always carefully read and follow all label precautions before applying insecticides.)
2. Promoting tree vigor through silvicultural methods such as thinning or promoting mixed-tree stands will help reduce the risks of an infestation.
3. Generally, budworm populations are usually kept under control by a combination of predators, parasites, climatic conditions, or insufficient food supplies.

Want to learn more about western spruce budworm? Please check out the following documents:

Western Spruce Budworm (136 KB PDF)
Western Spruce Budworm Poster (253 KB PDF)
Pages 3 through 12 of the 2005 Report on the Health of Colorado's Forests (7.52 MB PDF)

This section didn't quite descibe your tree's ailments? Check out our Sick Tree ID Guide to find out what's actually wrong.

You might also like to visit Colorado State Cooperative Extension's Horticulture Online.

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Insect and Disease Publications

Aphids on Shade Trees and Ornamentals (43 KB PDF)
Aspen and Poplar Leaf Spots (203 KB PDF)
Bacterial Wetwood (176 KB PDF)
Cytospora Canker (87 KB PDF)
Diagnosing Tree Disorders (146 KB PDF)
Dwarf Mistletoe Management (127 KB PDF)
Fire Blight (125 KB PDF)
Honeylocust Diseases (100 KB PDF)
Insects and Diseases Associated with Forest Fires (260 KB PDF)
Ips Beetles (298 KB PDF)
Juniper-Hawthorn Rust (48 KB PDF)
Leafmining Insects (128 KB PDF)
Mountain Pine Beetle (281 KB PDF)
Oystershell Scale (78 KB PDF)
Pinyon Pine Diseases and Insects (297 KB PDF)
Poplar Twiggall Fly (144 KB PDF)
Preventive Spraying for Mountian Pine Beetle (17 KB PDF)
Protecting Trees During Construction (84 KB PDF)
Shade Tree Borers (244 KB PDF)
Solar Treatment of Mountain Pine Beetle Trees (14 KB PDF)
Tent-Making Caterpillars (88 KB PDF)
Western Cedar Bark Beetles (62 KB PDF)
Western Spruce Budworm (136 KB PDF)

Use of Verbenone for Mountain Pine Beetle (47 KB PDF)
Product YEA for use on Mountain Pine Beetle (57 KB PDF)
Spraying Trees to protect against Mountain Pine Beetle (50 KB PDF)
Tree injections for Mountain Pine Beetle (48 KB PDF)

USFS Forest Insect and Disease Leaflets (FIDL)
FIDL Mountain Pine Beetle
FIDL Spruce Beetle

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