How to Beat Evergreen Borer Beetles Before They Attack Your Property

Evergreen Borer Beetles are on the rise in Denver, attacking some of your favorite pine and spruce trees. Rather than describing one species of insect, Evergreen Borer Beetles (EBB) refer to various species of tree boring beetles that afflict evergreen trees. Follow our guide below to learn more about how to spot EBB, the dangers borer beetles pose to your trees, and how to prevent an infestation on your property.

Before we jump into what you need to know about EBB, it’s important to know which types of trees are at a high risk of infestation. And more importantly, to determine if you have these types of trees on your property.

The Trees Most Affected by Evergreen Borer Beetles

Evergreen Borer Beetles have an appetite for more than a handful of Denver’s most lush and ornamental pine and spruce varieties. Below is a list of the pests’ absolute favorites and some key identifiers for each one if you’re trying to ID your property’s trees.

Ponderosa Pine 

With tall, straight, thick trunks, textured in scaled, rusty-orange bark that has split into big plates, the Ponderosa Pine is pretty easy to spot. Think you found one? Sniff around, their bark smells like vanilla or butterscotch! Examine and feel the needles. They are approximately 4-8 inches long and should feel thick and flexible. Typically there are three to a bundle, and the needles hang gently from their branches.

Austrian Pine

The first thing you’ll notice about the Austrian Pine is its shape. Young trees are pyramidal in shape, but become oval with age and, on some sites, flat-topped. Its rich green needles are dark and eye-catching. They contrast most of the other foliage around them. Austrian pine needles feel stiff to the touch. They have very little bend and are usually 2 to 4 inches long growing in groups of 2. 


Most fir and pine trees have downturned branches. In contrast, you’ll notice right away that Spruce trees have upturned branches. They also grow in a uniquely full and bushy shape. Another identifying feature is its vibrant and sought-after blue-green color.

Scotch Pine

Scotch Pines can range from bluish-green to medium green to yellow-green in color. They feature relatively short needles that are firm to the touch and grow in bundles of two. The needles stand out because of their strange twisted shape and bluish color. The entire tree itself is known to grow at contorted or odd angles.

Even with a handy guide, tree identification can sometimes be tricky. Our friendly and expert arborists can conduct a quick consultation on your property to identify your tree species and inspect for any signs of beetle infestation.

Types of Tree Borer Beetles Local to Denver

The next step in fighting off Denver’s local EBBs is to know how to identify them. Generally, you are going to identify which beetle you are up against by both the physical presentation of the insect and the appearance of the injuries they cause to the tree. 

Mountain Pine Beetle

Historically one of the most dangerous insects to trees on Denver’s front range, the Mountain Pine Beetle’s impact has lessened only slightly over the past 5-8 years. It has been recently overshadowed by the IPS beetle, but the Mountain Pine Beetle (MPB) is not to be underestimated. They are found in every corner of the state, lurking in the background, and a large outbreak of Mountain Pine Beetles is difficult to control.

Mountain Pine Beetle Identification:

  • Mountain Pine Beetles are just a quarter of an inch long.
  • Their tiny white larvae are the size of a grain of rice.
  • Adult beetles are rusty brown or black in color.

Fast Facts About Mountain Pine Beetles:

  • Native Colorado bark beetles that predominantly infest ponderosa pine, lodgepole pine, and limber pine.
  • Adults typically fly to seek new hosts in July through August.
  • MPB completes a generation within one year from egg to adult.
  • Attacking females initially prefer large-diameter trees until they are depleted from the forest.

Signs of Mountain Pine Beetle Infestation:

  • Needles on infested trees typically turn rust-colored.
  • Needles typically drop from branches the second summer after the tree has been infested.
  • Boring dust in bark crevices and on the ground immediately adjacent to the tree base is also a sign of bark beetles.
  • Popcorn-shaped masses of resin called “pitch tubes,” are caused by beetle tunneling and often found on the trunk.
  • Pitch tubes may be brown, pink or white.
  • Larvae on infested trees attract woodpeckers.
  • Check for woodpecker damage: stripped portions of the bark and accumulations of bark at the base of trees.
  • You will see small exit holes on the bark’s surface when an adult beetle emerges from an infested tree.

Pine Sawyer Beetle

This evergreen boring beetle is the primary carrier of the highly damaging Pine Wilt Disease. They are not very picky and will seek out and attack all sorts of Denver evergreen trees.

Pine Sawyer Beetle Identification: 

  • Adult beetles can grow to be 14-24 mm in length.
  • Pine Sawyer Beetles are black or brownish gray with white markings.
  • Spines on the exterior form a sort of armor.
  • Many Pine Sawyer Beetle varieties have horns.

Fast Facts About Pine Sawyer Beetles:

  • Pine Sawyer Beetle is notorious for spreading Pine Wilt Disease.
  • The Pine Sawyer Beetle is a carrier for the native strain of nematode during the hot summer months.
  • This beetle variety loves high altitudes.
  • Ponderosa Pines and Douglas Firs are its preferred habitat.
  • Beetles feed on the sapwood and heartwood of recently killed trees.

Pine Sawyer Beetle and Pine Wilt Disease

  • Infection and colonization of pines by Pine Wilt Disease start in June or July but observable symptoms don’t normally appear until late summer or fall.
  • Needles to initially turn grayish turn from gray-green to tan and eventually brown due to lack of water.
  • Dead needles remain attached to the tree through the winter.
  • On Scots pine, the entire tree usually wilts and dies within a few months.
  • Wilting on Austrian pines may at first only be a portion of the tree, but the wilting process may continue to prolong.
  • When cut, diseased wood is very dry to the touch.
  • Trees killed by pine wilt also develop blue staining in the wood.

White Pine Weevil

These overwhelming pests typically target spruce trees, and unlike most Evergreen Borer Beetles, they are active during winter months. Timing is everything when trying to stop the White Pine Weevil from infesting your trees.

White Pine Weevil Identification:

  • Adult beetles have a very distinct snout and are about .2 inches in length.
  • The larvae are long, with no legs, and are yellowish-white in color.
  • The beetle’s exterior is brown and scaly with white spots and wings.

Fast Facts About White Pine Weevils:

  • Injury by white pine weevil is almost entirely limited to higher elevation areas of the state and foothill areas.
  • The standard approach to manage white pine weevil is to spray insecticides in spring
  • A closely related species, Pissodes terminalis, causes similar injury to lodgepole pine in Colorado. This insect is sometimes called the lodgepole pine terminal weevil.

Signs of White Pine Weevil Infestation:

  • The white pine weevil causes visible injury in late spring.
  • Visible signs include new growth wilts and dieback.
  • The affected shoots wilt into a ‘shepherd’s crook’ form.
  • Needles often become lighter-colored before they ultimately die and drop.
  • Affected trees have stunted growth and develop a bushy appearance with multiple leaders.

Zimmerman Pine Moth

The Zimmerman Pine Moth does not discriminate between Denver evergreen species but deals serious damage to all trees in its path.

Zimmerman Pine Moth Identification:

  • Larvae are approximately an inch long and are an off-white color.
  • Adult moths are medium-sized.
  • Adults have gray and reddish wings with a zigzag design.
  • Adult moths are rarely sighted.

Fast Facts About Zimmerman Pine Moths:

  • Caterpillars of the Zimmerman pine moth damage pine trees by tunneling into the trunks and branches, often causing branches to break.
  • Scotch and Austrian pines are particularly susceptible to injury.
  • Evidence of injury are pale yellow, popcorn-like masses of sap that develop in response to feeding wounds.
  • Preventive insecticide sprays are effective when applied during periods when the caterpillars are exposed on the surface of the tree.

Signs of Zimmerman Pine Moth Infestation:

  • Damage is from an injury made by caterpillars who tunnel into the trunk and branches.
  • Tunneling produces irregular gouging wounds under the bark. 
  • Popcorn-like masses of sap ooze and collect on the surface where these wounds occur.
  • Sap is soft and will easily pull away from a recent injury.
  • Underneath an injury, you’ll find the tunnel of the feeding caterpillar. 
  • Damage usually occurs in the upper part of the tree.
  • Feeding is in the area where branches meet the trunk. 
  • Injury may result in limbs dying or breaking from the tree.

If you observe any of these warning signs it is critical that you reach out to our tree health experts. The life of your tree could depend on it!

Get An Accurate Diagnosis From An Arborist You Can Trust

With more information than ever online and at our fingertips, we’ve become accustomed to diagnosing all kinds of things – our failing AC unit, a hot water problem, even the rash that developed from yesterday’s yard work.

But tree health is not something that the average homeowner can diagnose on their own. In fact, timing is everything and if you waste precious time and misdiagnose your tree it can mean the difference between life and death for that plant.

Let our expert arborists evaluate your trees with a trained eye and make an educated recommendation for an effective treatment plan!

Preventative Action Denver Homeowners Can Take 

Unfortunately, a tree with an established borer beetle infestation is incredibly difficult to treat. In many cases, the tree will never fully restore to its original healthy condition.

Safeguarding a tree is the best course of action for tree species beetles love. Preventative measures include:

Soil injection 

Soil injection promotes overall tree health and limits stress drought. Beetles find an attraction with stressed trees, but strong well-cared-for trees can effectively fight off an attack by pests. Fielding Tree Care recommends repeating soil injection treatment twice per year, in the spring and fall. 

Regular Watering and Fertilization

Beetles like trees that are dry or without energy. One of the best ways to keep your trees safe is to schedule routine watering and fertilization throughout the year. Our experts can help recommend appropriate watering levels and the right combination of fertilizer to keep your trees happy and healthy.

Treatment For Infected Trees 

  • Trunk injection: 

Inject a trunk insecticide into a tree with an established infestation every two years to treat trees. Trunk injection can repel the beetles and prevent further harm to the tree.

  • Insecticide spray:

A bi-annual application of insecticide spray is a great treatment option depending on the size and condition of the tree. If the beetles are only just arriving and are topical, the spray can be very effective.

  • Tree removal:

If an infestation is too far along, we recommend you remove the tree. This is for the safety of all your other trees and your neighborhood. Beetles spread rapidly from one tree to the next. If you can’t get a threat under control, remove the tree ASAP so it does not further spread infestation and disease.

Hopefully you learned some new things about Evergreen Borer Beetles and can implement some of these tips to keep your evergreen trees happy! Get ahead of the borer beetles this spring and team up with expert arborists to fight off infestation before it begins.