Tree Insect Calendar

Got bugs on your trees? Please use the tree insect calendar below to identify the bugs that might be affecting your trees.

The Denver area is home to many tree insects — some harmful, some beneficial. Understanding each insect’s lifecycle is essential in treatment timing. Control product applications that are not well-timed waste money and time. Wet springs support the growth of many of the insects listed below. On the other hand, hot late summer days support the development of other pests. So it is best to pick a tree company, like Ross Tree, that has accredited professionals who know how to control tree pests and protect helpful tree insects and the environment.

Ross Tree Company abides by our motto, Integrity in Action, which means residential and commercial property owners can expect the correct use of tree insect control products needed for the job. Ross Tree has three International Society of Arboriculture Certified Arborists on staff to help identify tree pests and four Qualified Supervisors licensed by the Colorado Department of Agriculture to handle pesticide products. Check out our tree insect calendar below,  if one of these tree pests looks familiar, please fill out a request service form or call 303-871-9121 to make an appointment.

Tree Insects Found in Denver

SPRING

Emerald Ash Borer

The EAB arrived in Colorado and is here to stay. City foresters across the metro area expect residential and commercial property owners to manage the Ash on their property. EAB treatment is less expensive than removing a large tree, so act now to save your Ash.

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Lilac Ash Borer

The Lilac Ash Borer is native to Colorado and attacks White and Green Ash trees. Larvae damage the trees by tunneling into the trunk and lower branches, leaving ¼-inch holes in the trunk or lower branches of an infected Ash tree.

Ips Beetle

Ips Beetles are common in Colorado and are also known as Engraver Beetles. They damage Pine and Spruce trees. Ips Beetles grow under bark and eat girdling tunnels that cause dieback and kill trees. 

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Kermes Scale

Kermes scale is an oak tree pest. They grow over winter as nymphs and, in the spring, molt and become immobile scales. We use oil sprays in early spring when Oak trees are dormant and before they leaf out to treat Kermes Scale. 

Tree Aphids

Aphids produce honeydew when feeding on trees. Large infestations make copious amounts of this sticky substance which can be a nuisance. Call Ross Tree to find out the best way to control these pests in the spring.

Spruce Beetle Calendar

Spruce Bark Beetle

Large outbreaks of the Spruce Bark Beetle are challenging to control. All infested trees should be treated before beetle emergence in the spring.

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Tussock moth caterpillar

Douglas-Fir Tussock Moth

Individual, the upper crowns of high-value Douglas Firs trees are treated to control Douglas-Fir Tussock Moths. The best time to apply insecticides is early spring to protect new needle growth.

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Ponderosa Pine Sawfly Denver

Ponderosa Pine Sawfly

Direct control occurs in early spring when Pine Sawfly eggs begin to hatch, and their larvae begin to feed on the pine needles. 

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Pine Needle scale treatment Denver

Pine Needle Scale

Pine Needle Scale has several natural predators which check their spread. For treatment, we use crawler sprays in the spring to control this insect. Winter dormant oils work in the winter, too.

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Striped Pine Scale treatment Denver

Striped Pine Scale

For outbreaks, the management of this Scale is similar to those for Pine Needle Scale. 

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Zimmerman pine moth treatment

Zimmerman Pine Moth

Direct control occurs in early spring when Pine Sawfly eggs begin to hatch, and their larvae begin to feed on the pine needles.

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Elm Leaf beetle treatment Denver

Elm Leaf Beetle

Wet springs support large populations of Elm Leaf Beetles. In early spring, female beetles begin laying masses of yellow eggs on the undersides of leaves. They hatch, producing tiny, black larvae that chew little holes in the leaves.

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Elm- Leaf Miner treatment

Elm Leaf Miner

The miner emerges in the spring and slits an opening to lays eggs on the leaves’ upper surface. Eggs hatch about a week later, producing brown-headed white larvae that tunnel into the leaves’ soft tissues.

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European Elm Flea Weevil treatment Denver

European Elm Flea Weevil

These tiny reddish insects create pinhead-sized, round holes in the foliage. As the insects eat, these holes enlarge, forming more noticeable holes. These holes show this weevil’s presence. They get their name when disturbed since they jump like fleas.

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Fireblight Treatment in the Spring

Fireblight

Fireblight infection will make leaves and twigs appear burned or scorched and will cause blossoms to turn brown and appear water-soaked. Spring is a great time to treat with PHOSPHO-jet, which will help promote tree defense responses.  

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SUMMER

Japanese Beetle

Adult Japanese Beetles attack Linden, Horsechestnut, apple, American Elm and Norway Maples. Japanese Beetle leave a characteristic skeletonizing pattern on leaves when feeding. They lay their eggs in turfgrass and their grubs damage lawns. Mid-summer is the best time to treat for Japanese Beetles. Homeowners should use a treatment method that lowers the risks to bees. Call Ross Tree to find out the best way to control these pests.

Mountain Pine Beetle

The Mountain Pine Beetle is ubiquitous to the Colorado mountains. This beetle has killed millions of pine trees in the mountains. They can also attack trees in mountain yards of urban areas. The Mountain Pine Beetle develops in Ponderosa, Lodgepole, Scotch, and Limber Pine Trees. Homeowners who see popcorn-shaped masses of resin on their trees should give us a call.

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European Elm Scale

European Elm Scale is a soft scale insect that attacks Elm and Hackberry trees. Heavy infestations produce large amounts of honeydew which turns into a grayish/black-colored sooty mold. Homeowners should call us when honeydew falls from affected trees onto patios, decks, and vehicles. We’ll apply soil products to treat European Elm Scale in early summer.

Honeylocust spider mite treatment Denver

Honey Locust Spider Mites

Hot summers support large populations of Honey Locust Spider Mites. Signs of Mites include discoloration of leaves, leaf curling, and premature dropping of leaves or needles.

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FALL

Walnut Twig Beetle

The Walnut Twig Beetle is a carrier of a fungus that causes Thousand Cankers Disease (TCD) in Walnut Trees. The fungus causes small, dead areas in the bark called cankers that girdles the branches until the tree dies. There are no effective treatments. The best course is tree removal and it is important that the tree debris be processed professionally to avoid the spread of TCD.

WINTER

Oystershell Scale

We use horticultural oils when trees are dormant to kill scale eggs. We recommend using other control products during scale outbreaks. Dormant oils effectively treat this insect. 

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Fireblight Canker

Fire Blight Treatment

Winter is a good time for Fire Blight treatment because there is no need to sterilize the tools between cuts. For more information about Fire Blight, check out Ross Tree’s Fire Blight Handbook.

Pine Needle Scale Treatment Denver

Pine Needle Scale

Heavy infestations cause premature needle drop and can kill branches and even young trees. Pine Needle Scale targets Mugho Pines in Denver. Dormant oils effectively treat this insect. 

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Giant Conifer aphid treatment Denver

Giant Conifer Aphids

These aphids usually feed in large groups on the sap of twigs and branches. Heavy infestations cause foliage to yellow and produce large deposits of honeydew. Dormant oils effectively treat this insect. 

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Leaf Curl Ash aphid treatment Denver

Leaf Curl Ash Aphid

Feeding by this aphid causes Ash leaves to curl and thicken. Some adults form wings in July and fly around in the fall to other trees. Dormant oils effectively treat this insect. 

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Honeylocust spider mite treatment Denver

Honeylocust Spider Mite

Heavy infestations of Honeylocust Spider Mites turn Honeylocustleaves an off-yellow color and causing premature leaf shed. Dormant oils effectively treat this insect. 

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Leaf Curl Ash aphid treatment Denver

Leaf Curl Ash Aphid

Feeding by this aphid causes Ash leaves to curl and thicken. Some adults form wings in July and fly around in the fall to other trees. Dormant oils effectively treat this insect. 

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Maple aphid treatment Denver

Boxelder And Maple Aphids

These aphids are about 1/10 inch long, with yellowish-green marked brown bodies with spine-like hairs and hairy antennae. They overwinter as eggs so we apply dormant oils to treat this insect. 

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