Pests in the Pines: Identifying and Managing Tree Pests in Fort Collins

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Identifying and Managing Tree Pests in the Pines

Pinon pitch mass borer attacks weakened evergreen trees. It usually kills the terminal leader but can disfigure other branches. Preventing injury and promoting rapid growth will help trees resist attack.

Symptoms include twisted and distorted new growth on fir; needles defoliating early; bark thinning with a rough appearance; and spindle-shaped galls on branches and trunks.


Often mistaken for leafhoppers, plant bugs or caterpillars, aphids are soft-bodied pear-shaped insects that can be green, black, red, yellow, or gray. Adult aphids are usually wingless but may develop wings when populations become too high or in spring and fall.

Aphids damage plants by sucking sap from the stems and leaves. This drains the plant of vital nutrients and water. Infested leaves wilt, curl or twist and may turn yellow. Younger plants that are heavily infested with aphids may produce deformed flowers or fruit and experience stunted growth.

Early detection of aphids is crucial for managing them effectively. Fort Collins CO tree service providers recognize that small and localized infestations can be addressed by employing measures such as spraying with high-pressure water. However, when infestations become widespread or are growing rapidly, it is advisable to resort to systemic insecticides like Safari or Criterion. Systemic pesticides, as recommended by Fort Collins CO tree service experts, are absorbed by the plant and travel throughout the entire system. When used according to instructions, these systemic insecticides can efficiently eliminate aphids and other damaging insects, ensuring the health and well-being of trees.

Pine Bark Beetles

Pine bark beetles (Dendroctonus frontalis) are a native species that attack the outer bark of ponderosa and coulter pine trees. They are particularly active in years with warm fall temperatures and drought.

Once beetles mate they tunnel under the bark to lay eggs, which hatch into larvae that feed in the phloem tissue. This damages the tree, girdles it, and allows fungus to block the phloem transporting sugars downward from the crown and starve the tree of moisture.

The beetles can be controlled by timely removal of infested trees for salvage and by spraying unmerchantable infested material with an insecticide. Symptoms of infestation include a general decline in the tree, discoloration of needles or leaves, and piles of boring dust in bark crevices and on the ground around the base of the tree.

Pine Weevils

White pine weevils (Pinus strobus) are indigenous to Colorado and typically attack trees that are stressed by drought, other insects, or human activities. The weevil is one of the most important forest insect pests in North America. In a mature spruce or pine forest, outbreaks are usually caused by natural causes such as wildfire or windthrow, or by human activities such as clearing, logging, and planting.

Weevils overwinter in the litter of the ground, and emerge in spring to infest hosts. Infested branches wilt and die, with feeding cavities visible in the bark. Females lay eggs in the bark, and larvae feed in the cortex until they pupate. Adults chew their way out of the tree, leaving exit holes. One generation is produced each year.

Preventative spruce tree treatments include regular watering (at least 10 gallons per inch of trunk diameter) and spray applications of the weevil-specific insecticides bifenthrin (Talstar, Onyx), permethrin, or cyfluthrin. Arborists with State pesticide applicator licenses can apply these products, as directed, in spring to infested trees.

Spruce Ips Beetle

Spruce ips beetles attack and kill conifer trees (including spruce) by tunneling under the bark. They are especially damaging in dry and stressed spruce stands and can kill individual trees and whole stands. Symptoms of an ips infestation include yellowing or browning needles and small, round emergence holes that are surrounded by reddish dust.

Ips beetle attacks depend on a number of factors, including weather conditions and availability of new breeding sites. Like other bark beetles, spruce ips beetles prefer to breed in felled host trees with low defenses and rely on pheromone-mediated behaviors to increase attacks until attack densities overwhelm tree defenses.

Adult spruce ips beetles are 1/8 to 3/8 inch long, reddish-brown to black and have a pronounced cavity at the rear end of the body. They can be distinguished from dendroctonus beetles by their gradually curved wings and smaller, more rounded appearance. Ips beetles also have a broader shaped head and less distinct spines.