303-378-8000‬ info@dlcarbor.com

Tree Insect Calendar

Check out what is bugging your trees!

Tree Insect Calendar

This handy tree insect calendar will help you identify what’s bugging your trees. DLC Arbor Services has one of the few ISA Certified Master Arborist in Denver. We are constantly monitoring new or re-emerging insects and diseases and will advise action when necessary.

Got a tree insect problem and need it treated? Click here to fill out a tree service request form, or give us a call at 303-378-8000.

Japanese Beetle

This insect is now radiating out of Cherry Hills Village into the entire Denver-metro area. It is a lawn insect in the grub stage. In the summer, when it becomes an adult, it damages plants, trees, vines and potted flowers. DLC Arbor Services will recommend a treatment based on the type of plant that’s infected.

Emerald Ash Borer

The time to treat for the Emerald Ash Borer is now. Ash trees have no natural defense against the EAB. Since it can take three to five years for an untrained eye to detect the EAB, by the time you notice the bug, it is too late to save the tree. DLC Arbor’s experts can provide you with treatment options.

Ash/Lilac Borer

This common parasitic wasp has plagued Ash trees with trunks less than 12 inches in diameter. It can be difficult to find an Ash tree without it. Although fatal if left untreated, it can be controlled with a combination of insecticide and fertilizer.

Ips Beetle

After several years of without problems, the Ips Beetle is killing Colorado Blue Spruce again. Prevention is the only treatment. Once Ips Beetles attack a tree, they are unstoppable and eventually kill the tree. Ips only affect Colorado Blue Spruce in the Denver area at this time. This insect spreads to other trees when the temperature is above 50°. Treatment consists of two sprays per year.

Kermes Scale

Kermes Scale is a large insect that attacks the twigs of certain oak trees. Symptoms of infestation are most obvious when branch tips fall off in great numbers during May and September.Kermes Scale is often confused with squirrel damage. DLC Arbor has great success treating this tenacious insect with a combination of systemic insecticides.

Oystershell Scale

Oystershell Scale is a tiny insect that lives under a protective cover on the leaves or bark of its host plant. It can infest a variety of plants but frequently lives on aspen trees. It’s common to find them on only one stem of a tree and not on any other part of the tree. Their shell (scale) protects them from insecticide sprays, so the best control method is systemic insecticide injections or difficult-to-time trunk sprays during their “crawler stage” from May to June. If left untreated, oystershell scale can eventually kill the tree.

Elm Leaf Beetle

The Elm Leaf Beetle is a very common insect plaguing Elm trees in Denver. The beetle and its larvae eat the leaves of a tree. DLC Arbor has the newest treatment options available.

European Elm Scale

The European Elm Scale is a very common insect plaguing American Elms that is now resistant to the typical insecticide used to control it – neonicotinoids. This soft scale pest secretes honeydew that covers cars parked beneath the infested trees, and causes black “sooty mold” that turns the bark black. Branch die-back is typical. There are new treatment options available.

Pine Borers

Pine Borers include Mountain Pine Beetle, Zimmerman Pine Moth, Piñon Pitch Mass Borer and Turpentine Beetle. They all dig tunnels into the tree and can cause damage from limb breakage to tree death. Most cause pitch to ooze from the hole and are treatable if detected early.

Peach (Fruit) Tree Borer

The Peach Tree Borer is the most damaging pest of peach, cherry, plum and stone fruit trees. It can weaken or kill trees. Adults bore holes in the base of the tree and roots. Symptoms include a jelly-like ooze at the base of the trunk. Spring is the best season to start controlling and will not affect the fruit.

Boxelder Bugs

If you have a boxelder tree, you have Boxelder Bugs. In the fall, this species congregates in large numbers on the south side of trees, buildings and rocks exposed to the sun. It is during this period that you may become aware of the insects. Adult Boxelder Bugs will frequently attempt to enter cracks and crevices in the walls to secure an over-wintering site in homes. Systemic insecticide application in the spring will help control the bug.


Aphids are soft bodied insects that suck sap from the leaves and live on almost any type of plant. Their damage ranges from the nuisance of a sticky substance called honeydew and the curling of leaves to branch dieback. In rare cases, Aphids can kill the tree. Control methods are based on the plant species.

Fire Blight

Fire Blight is a bacteria that infects pome fruit trees such as apples or pears. Luckily, stone fruit trees, like cherry, plum or peach, do not get fire blight. Fire Blight, unfortunately, has spread across Denver and has infected most crabapple trees to some degree. It can be hard to treat, but DLC Arbor has had great success treating fire blight with a combination of treatments.

Mountain Pine Beetle

The Mountain Pine Beetle (MBP) has returned to pre-outbreak levels and is no longer an issue. The MPB and their larvae disrupt the movement of food and water throughout the tree. Additionally, the adult beetles carry a blue stain fungus that harms the tree. The only treatment is preventative, which kills the beetles before they infest the tree. 

Ladybugs - The More the Merrier

The only nice bug on this list! Ladybugs are very beneficial for your yard and trees. We love them so much, in fact, they’re our mascot! Look for them on our trucks. In the spring, buy several packages of live ladybugs and let them loose in your yard.


DLC Arbor Services

123 Vallejo St.

Denver, CO 80223