Ross Tree has noticed infestations of tree borers in the field this spring in both conifers and hardwoods. Our certified arborists believe that winter droughts in the Denver area create stress making trees easy targets for these insects. It is extremely dry in Denver this season. The City’s lack of snow in 2021 is now in the record books. A local news program reported it finally snowed on December 10, equating to 232 days without measurable snowfall.

Proper maintenance goes a long way to help trees ward off these borers. We strongly recommend that all yard trees be watered and fertilized during the winter months to keep them healthy. Winter pruning discourages harmful insects in the spring. Thriving trees produce defensive chemicals in response to borer wounding, weakening, or killing borer grubs. They also stimulate callus wound tissue growth that can encapsulate young borers. Well-hydrated conifers produce large amounts of resin that drowns invading insects. Also, proper tree maintenance sets trees up for a robust growing season.

Pine borers in Denver

What Tree Borers are Active in Denver this Spring?

After the eggs hatch in early spring, the larvae burrow into the inner bark and sapwood to grow. If the tree is weak, the larvae can do a considerable amount of damage to its vascular systems, eventually girdling the plant. During large infestations, bores attack healthy trees, too. We are finding the following borers in large numbers:

  1. Banded Ash Borer

    Banded ash borer denver
    The Banded Ash Borer (Neoclytus caprea) is among the first Longhorned beetles to emerge in the spring. Ash is the most common tree the borer attacks, but the insect is also found on Oaks, Elms, and Lindens. The borers favor trees that are in decline or have died. The Banded Ash Borer is a close relative to the Redheaded Ash Borer. Both are native to North America.

  2. Lilac And Ash Borers

    Lilac-ash borer Denver
    Lilac/Ash Borer (Podosesia syringae ) is native to Colorado. Its larvae tunnel into the trunks and lower branches of Ash trees. Feeding damage is often found in the mid and upper crown of trees above areas treated with contact insecticides. So, it is best to use systemics to treat the whole tree.

  3. Peach Tree Borer

    Peach tree borer Denver
    Peachtree Borer (Synanthedon exitiosa) is the most destructive insect pest of stone fruit trees such as Peach, Cherry, and Plum. Their grubs chew underneath the bark at the tree’s base, leaving wet or oozy sap spots. Insecticides applied to the lower trunk target the eggs and early larval stages on the tree’s bark. 

  4. Mountain Pine Beetle (MPB)

    .Mountain Pine Beetle Denver
    The MPB (Dendroctonus ponderosae) has killed millions of trees across Colorado. These small native Colorado bark beetles predominately infest Ponderosa, Lodgepole, and Limber pines. However, they will attack other pines species when beetle populations explode, including ornamental trees. Preventive insecticide sprays are effective, but timing is critical to protect high-value yard pines

  5. Pinon Pitch Mass Borers 

    Pinon Pitch Mass Borers in Denver
    The Piñon Pitch Mass Borer (Dioryctria ponderosae) attacks Piñons across the State. However, occasionally they do infest other pines. In landscapes, overwatering and crowding make trees susceptible to attack. Preventive trunk sprays can reduce attacks but must be repeated over time to be effective.

  6. Zimmerman Pine Moth

    Zimmerman Pine Moth in Denver
    Scotch and Austrian pines are particularly susceptible to injury by the Zimmerman Pine Moth (Dioryctria zimmermani). Affected trees form popcorn-like masses of sap on feeding wounds. Preventive insecticide sprays are effective when applied before the caterpillars burrow.

  7. Ips Beetle

    Ips Beetle in Denver
    There are eleven Ips Beetle species in Colorado, and all can kill Pines and Spruces growing in the Denver area. Once the beetle attacks a tree, the tree must be removed because there is no cure. The Ips attack drought-stressed evergreens. So, the key to preventing this insect from attacking yard trees is to follow sound tree maintenance practices (watering, fertilizing, and pruning) that promote healthy growth. Sprays and systemics provide year-long protection.


Other Tree Insect and Disease Concerns

Thyronectria Cankers

Consecutive winter droughts have brought on an onslaught of Thyronectria Cankers (Thyronectria austroamericana), found on Honeylocusts across Denver. If found on the main trunk, the tree needs to be removed. To learn more about protecting Honeylocusts trees against this canker, please check out our blog titled “How To Deal With Cankers On My Honeylocust Trees?

Emerald Ash Borer (EAB)

The EAB (Agrilus planipennis) broke out of its quarantine in Boulder two years ago and is now found in many cities along the Front Range. City foresters do expect homeowners to manage their yard Ash. For more information about this highly destructive borer, check out our EAB Handbook

Healthy trees can resist all the insects and diseases mentioned above. Young trees should be wrapped from November to April to prevent sunscald. Pruning out any dieback discourages tree pests. Call Ross Tree at 303-871-9121 or click here to fill out a tree service request form to start a tree management program today.