Evergreen plants, such as pines, spruces, firs, junipers, and cedars, provide year-round structure and color to the landscape. Despite their hardy appearance, these conifers are frequently targeted by insects that feed on their needles, sap, or bark. Infestations often proceed unnoticed until damage becomes widespread, leading to a decline in plant health. Understanding the specific signs and implementing timely, targeted treatments is the most effective approach to protecting these assets. This guide provides methods for identifying and managing the most common pests that affect evergreen trees and shrubs.
Recognizing Signs of Infestation
The initial evidence of a pest problem often appears as a change in the color or density of the needles. Needles may show discoloration, turning yellowish, grayish, or bronzed, indicating that sap-sucking insects are active and drawing nutrients from the foliage.
Premature shedding of older needles, particularly those on the interior of the branch, is another common symptom. While evergreens naturally shed some interior needles annually, excessive drop suggests stress caused by feeding activity. A general lack of vigor, stunted new growth, or thin foliage signals that the plant is struggling with an infestation.
Visible residues also signal pest presence. These include sooty mold, which grows on honeydew—a sugary waste product excreted by sap-feeding pests like aphids or scale insects. Honeydew leaves a sticky film on the needles and branches. Additionally, fine, silky webbing stretched between needles or small bumps on the bark can indicate specific types of insects.
Identifying the Most Common Evergreen Pests
The three most frequently encountered groups of evergreen pests are mites, scale/adelgids, and sawflies. Each leaves behind a distinct signature of damage.
Mites
Mites, such as the Spruce Spider Mite, thrive in the cooler temperatures of spring and fall. Their feeding causes a characteristic “stippling” effect, where needles develop tiny bleached or yellowish spots from the removal of chlorophyll. Heavy infestations create fine, silken webbing that covers the needles and small twigs, especially on lower branches. To test for mites, shake a suspected branch over white paper; if small specks move rapidly across the surface, mites are present.
Scale and Adelgids
Unlike mites, scale insects and adelgids are stationary pests in their adult stage, appearing as small, waxy bumps or cottony masses on the needles or bark. The Pine Needle Scale manifests as tiny, white, oyster-shell-shaped specks directly on the needles, making the foliage look whitewashed from a distance. Balsam Woolly Adelgids attack true firs, appearing as small, white, woolly tufts primarily on the lower trunk and branch nodes. Their toxic saliva causes a defensive swelling of the nodes, known as “gouting,” which restricts nutrient flow.
Sawflies
Sawflies are defoliators whose larvae resemble caterpillars with distinct black heads. They feed in groups, quickly stripping the older needles from a branch while often leaving the current season’s new growth untouched. The European Pine Sawfly typically feeds in the spring, initially skeletonizing the needles before consuming them entirely. This results in branches with a sparse, “lion’s tail” appearance.
Immediate Non-Chemical Control Solutions
Initial pest control efforts should focus on non-chemical methods to immediately reduce pest populations. One simple physical control is using a strong jet of water to dislodge pests from the foliage. This method is particularly useful against mites and aphids, which are physically knocked off the plant and often cannot climb back up.
Horticultural Oils and Soaps
Horticultural oils and insecticidal soaps offer low-impact solutions that work through physical action rather than internal poisoning. Oils smother soft-bodied pests like mites, scale crawlers, and adelgids by blocking their breathing pores. Soaps contain potassium salts of fatty acids that disrupt the pest’s cell membranes, causing dehydration. Both oils and soaps must thoroughly coat the pest to be effective, requiring complete coverage of all plant surfaces, including the undersides of needles. Apply these products when temperatures are moderate and the plant is not under drought stress to prevent foliage burn.
Manual Removal
Manual removal and pruning can significantly impact localized infestations, especially for pests like scale and sawflies. Heavily infested branches should be selectively pruned and removed to eliminate egg masses and clustered feeding populations. For large, visible pests such as sawfly larvae, hand-picking and dropping them into soapy water provides instant, targeted control.
Targeted Chemical Treatments and Preventative Care
When non-chemical methods fail to manage a severe infestation, targeted chemical treatments are necessary. These treatments focus on the pest’s most vulnerable life stage.
Chemical Treatments
Systemic insecticides are absorbed by the plant’s roots and transported throughout its vascular system. They are highly effective against internal feeders and stationary sap-suckers like scale and adelgids. Applying a systemic soil drench in early spring allows the chemical to circulate, poisoning pests that feed on the sap for up to a year. Contact insecticides, such as those containing pyrethrins, are best used when pests are actively moving, like scale crawlers or young sawfly larvae. Timing is crucial, as applying them when the pest is protected or the plant is dormant is ineffective. Always consult product labels to ensure the chemical is appropriate for the specific pest and to avoid harming beneficial insects.
Preventative Care
Long-term preventative care enhances the evergreen’s natural defenses and reduces susceptibility to outbreaks. Ensure the plant receives proper water, especially during dry periods in late fall and winter, to mitigate drought stress. Applying mulch around the base helps regulate soil temperature and moisture, promoting root health. Correct pruning techniques improve air circulation within the canopy, creating a less favorable environment for pests. Maintaining the overall health of the evergreen makes it more resilient and better equipped to withstand minor pest pressure.