Insect & Disease Control

Our experienced, trained Arborists know what insects affect what trees and can prescribe the safest and most effective treatments for controlling damaging levels of insects and diseases. We do not attempt to control all insects all the time, but instead, address only those pests that are likely to cause health issues with your landscape plants.

When our applicator teams arrive at your property you can be assured that their knowledge and training is among the best in the industry, which facilitates a safe, thorough and professional application for your property. Call us to learn about all the ways a PHC program can benefit your Colorado landscape.
Learn more about our Natural Control Options »

Insect & Disease Calendar>
The chart below shows some of the more common insects and diseases that attack and damage our trees, shrubs and lawn in this area along with a brief description of each. These are just a few of the more damaging insects and diseases.

Download our printable Bug and Disease Calendar >>

Timing can vary depending on weather, location, pest emergence and other variables. We hope this will assist you in becoming more aware of these potential problems. Insect and disease control is only one tool of overall landscape care. A complete maintenance program is the key to healthy trees, shrubs and turf. Please call us if you have questions on any specific problem or for general Plant Health Care information.

Questions? Call our Denver Office: 303.232.0666
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Aphids Sap sucking insects causing foliage to become sticky and distorted on many trees, shrubs and evergreens. A sooty mold often develops that may discolor the area below. APRIL – OCTOBER
Ash / Lilac Borer Larvae burrow into trunks and excavate galleries in young and stressed Ash trees, causing severe limb die back and possible death. APRIL – MAY
Ash Sawfly
Green larval worms feed on the leaves of Ash trees, potentially defoliating the entire tree. MAY – JUNE
Boxelder Bug This insect is primarily a nuisance that does little harm to the Boxelder trees. Very difficult to control effectively. Control can be applied any time adults are present. MARCH – JULY
Bronze Birch Borer Larval feeding destroys tissue of trunks and branches. Preventative treatments are effective for control. APRIL – JULY
Codling Moth Frequently referred to as “The worm in apples”. Treatments are most effective just after full blossom, but can extend through harvest when maximum control is required. APRIL – JULY
Cottony Maple Scale Large cotton-like egg masses. Can be found on Maple, Locust, Cotoneaster, Viburnum and other trees and shrubs. APRIL – SEPTEMBER
Cottonwood / Poplar Borer Affects weakened Cottonwood, Poplar and Aspen trees, causing drill like holes in trunk. Death of affected tree is common. JULY – AUGUST
Crown Borer Attacks the lower trunk of Peach and Plum trees, causing jelly-like masses. Can cause decline or death of tree. APRIL – MAY
Elm Bark Beetle The carrier of Dutch Elm Disease; also destroys the tissue under the bark. Mostly affects American and English Elms. APRIL – JULY
Elm Leaf Beetle The larvae feeds in between the veins, skeletonizing the leaves and the adult beetle chew holes in the leaves. Heavy feeding can cause defoliation. JUNE
Elm Leaf Miner Larvae appear inside new leaves as they develop appearing as brown and transparent pockets in the leaf. Can also cause premature leaf drop. Can affect many trees including Elm, Birch, Boxwood, Hawthorn and Roses. MAY
Emerald Ash Borer Attacks all Ash species. Early symptoms of an infestation include dead branches near the top of the tree, or leafy shoots growing out from the base of the trunk. There will be “D” shaped exit holes and bark will split exposing serpentine like tunnels. Learn more & view photos here » Best controls are achieved with preventative treatments from MARCH –MAY
European Elm Scale Immature stage will secrete large amounts of sticky honeydew and cause sooty mold that will discolor branches and the ground under them. Will cause twig and branch die back. MARCH – SEPTEMBER
Honeylocust Plant Bug /
These two insects together will feed on new Honeylocust leaves as they emerge and will cause distorted looking leaves. MAY- JUNE
IPS Engraver Beetle Beetles make small holes into the bark and create galleries underneath. Saw dust like frass is emitted. Often starts at
the top. This small beetle mass attacks stressed Pine and Spruce trees causing them to die quickly. FEBRUARY – SEPTEMBER
Japanese Beetle A newcomer to Colorado. Can feed on almost any plant including turf roots. Seems to prefer certain vines, roses and berry plants. Best controls requires monitoring and a full plant health care program. MARCH – SEPTEMBER
Kermes Scale This insect will cause tufts of Oak leaves to fall. Heavy infestations will cause branch die back and tree death. MARCH – SEPTEMBER
Mites Many species that can damage almost any plant including turf. Best controls are achieved with a Plant Health Care
Mountain Pine Beetle Primarily a mountain problem but has migrated to the front range, attacking and killing Scotch, Ponderosa, Mugo Pine and Lodgepole Pine trees. MAY – JUNE
Oak Leafroller This defoliator periodically builds up to high populations in the spring, defoliating many groups of Gambel Oak trees. MAY – JUNE
Oystershell Scale Affects Aspen, Ash, Lilac, Cotoneaster and other plants. Best treated in crawler stage. JUNE
Pine / Juniper Needle Scale Visible as small white specks on some Pine, Spruce and Juniper needles causing severe tissue damage to those needles.
Not to be confused with the natural resin specks on Bristlecone Pine trees. APRIL – SEPTEMBER
Poplar Scale This scale is becoming a serious problem on many Aspen trees requiring special control. JUNE – JULY
Red Headed Ash Borer Relatively new to the Front Range. Drill holes evident in trunk. Can severely damage younger Ash trees. APRIL – SEPTEMBER
Spruce Gall Adelgid Causes a brown cone like growth on the tips of Spruce trees. Damage is mostly cosmetic. APRIL – MAY & AUGUST – SEPTEMBER
Striped Pine Scale A soft scale causing obvious thinning and decline of Scotch and Mugo Pine trees. MARCH – MAY
Tussock Moth This serious defoliator of Spruce and Fir trees can kill a tree if it is repeatedly hit. MAY – JUNE
Turpentine Beetle Attacks the lower 8′ of stressed Pine tree trunks causing obvious saw dust like frass filled pitch tubes. APRIL – JULY
Walnut Twig Beetle Attacks twigs and branches of Walnut trees, plus carries a deadly fungus known as 1000 Canker disease. Effective preventative controls have not yet been established. APRIL – JULY
White Pine Weevil This beetle with a snout hits the top terminal of Spruce trees and causes the top to die and crook over. Repeated attacks cause the top of a Spruce to be deformed. MARCH – APRIL
Zimmerman Pine Moth Larvae feed on and cause distressed tissue around Pine tree branches where they connect to trunks, causing weakened branch attachment and failure. APRIL – AUGUST
Powdery Mildew A fungal disease which infects leaves of trees and shrubs such as Apple, Lilac and Roses. Leaves will have a light powdery look. Fungicide applications can help. APRIL – AUGUST
Anthracnose Several species attack trees such as Sycamore, Ash, and Maple causing significant stress and potential death. MARCH – JUNE
Cytospora Canker Some of the more aggressive species infect and kill Aspen, Cottonwood, and Mountain Ash. MARCH – APRIL & JUNE – JULY
Dutch Elm Disease This disease has been killing American Elm trees in Denver since 1970. Preventative programs can be very effective for control. MARCH – APRIL & JUNE – JULY
Fireblight Aggressive bacterial disease of Apple, Crab-apple, Pear, Peach, Mountain Ash and Hawthorn. MARCH – JULY
Leaf Spot Leaf spot is often the cause of discolored leaves falling from Aspen and Cottonwood trees in July and August. MAY
1000 Canker Disease This disease is vectored by the Walnut Twig Beetle and is killing Walnut trees at an alarming rate. APRIL – SEPTEMBER
Ash Aphids, Ash Borer, Red headed Ash Borer, Oyster Shell Scale and Ash Sawfly
Apple / Crab-apple Aphids, Mites, Fireblight, Powdery Mildew and Codling Moth
Aspen / Cottonwood / Poplar Aphids, Leaf Spot, Cytospora Canker and Cottonwood / Poplar borer
Boxelder Aphids and Box Elder Bug
Birch Aphids and Birch Borer
Elms Aphids, Mites, Elm Leaf Beetle, Elm Scale, Elm Leaf Miner, Dutch Elm Disease and Elm Bark Beetle
Hawthorn Aphids, Mites, Leaf Miner and Mealy Bug
Linden Aphids and Mites
Locust Mites and Leaf Hopper
Maple Aphids, Cottony Maple Scale and Anthracnose
Pear Fireblight * Some species are more susceptible to fireblight than others
Peach / Plum Aphids and Crown Borer
Juniper Aphids, Mites and Needle Scale
Pines Aphids, Mites, IPS Engraver Beetle, Pine needle scale, Zimmerman Pine Moth, Striped Pine Scale, Pine Bark Adelgid, Mountain Pine Beetle, Turpentine Beetle, Aphids and Mites
Oaks Aphids, Mites, Kermes Scale and Oak Borer
Spruce Aphids, Mites, IPS Engraver Beetle, Tussock Moth, Aphid Gall, Mites and Cytospora Canker
Walnut Aphids, Walnut Twig Beetle and 1000 Canker Disease
Willow Aphids, Cytospora Canker and Aphids
Ascochyta Symptoms of this leaf blight may appear very quickly (less than 12 hours) as bleached leaf tissue during periods of hot, dry weather that is preceded by cool, rainy conditions. Large patches of infected tissue can quickly consume a lawn.
Dollar Spot This fungal disease develops throughout the season and is most active during periods of warm days and cool nights in the spring, early summer and fall. Close examination may reveal a cobweb-like mycelium that forms as the fungus develops. Dollar spot may be spread into new areas by mowers, water and foot traffic.
Grubs The white colored larvae that feed on turf roots causing major turf damage throughout Colorado. This group of insects develops in various adults such as Chafer Beetles, Japanese Beetles and June Beetles, among others. Many of these insects damage turf areas in both the larval and adult life stage.
Mites There are thousands of species of mites in the environment and many feed on turf areas. Damage can occur during the entire year because some species favor cool temperatures while others enjoy warmer temperatures.
Necrotic Ring Spot This is the most destructive disease of bluegrass in Colorado. Distinctive circular patches of straw colored grass develops from June to August. This disease will intensify and spread if left untreated.
Sod Webworm Several species of caterpillars feed on turf roots causing significant die back in turf areas. Damage will often begin to show up in the early spring.
Weeds The most prevalent and problematic weeds in our lawns include Clover, Spurge, Tall Fescue, Thistle, Wild Violet and Bindweed.

For more information on plant health care, visit the
Colorado State University Extension’s Website »