A number of insect pests can threaten the aesthetics and functionality of conifers in the landscape. Successful management of these pests depends on early detection before they reach injurious levels. This can best be accomplished through frequent inspections, proper pest identification and an understanding of insects’ biology and behavior.
Depending on the size of the tree, count on it taking at least 15 minutes per tree to do an inspection. Comparing the tree in question to nearby trees of the same species is helpful in spotting problems. Fortunately, it doesn’t require complex or expensive tools, mostly just your eyes in combination with experience and training.
There are several ways of approaching a systematic inspection of conifers. Perhaps the one most logical involves first looking at buds and stems. On most conifers, buds are at the periphery, making them the first plant part the inspector comes into contact with. As such, they are also the easiest to inspect for insect damage, disease or other abnormalities. From the buds, the next step is to direct your attention along the stems. Insects can be found just about anywhere on a conifer, but the past three years of growth are where active infestations are likely to occur.
Next, take a step back and examine the needles. It’s best to start at the top of the tree or shrub then work your way down (or vice versa), rather than letting your eyes meander around. Finally, check out the trunk. Trunk inspection is the most difficult in terms of spotting problematic areas, because several benign or non-insect-related maladies are likely to be similar in appearance and cause confusion. External sap flow from wind damage and birds hunting for insect prey are good examples.
Frequent inspections are a hallmark of IPM and are critical to the effective control of insect pests of pines and other conifers. Regardless of whether you end up scheduling a pest control application, frequent and regular inspections should be part of your overall service plan.
Buds and stems
Pine tip moth — If you’ve done a good job inspecting the buds and stems, you may have seen evidence of pine tip moth feeding. All species of two and three-needle pines are potential hosts, with most severely injured including Austrian, pondersosa, Scotch and mugho pines. Initially, pine tip moth caterpillars bore into needles, but later bore into the buds and shoots as they grow. Symptoms include brown bud tissue, a small hole in the adjacent stem and soft, sticky exudates from feeding activity. Infested tips readily crumble when handled. Because conifers primarily grow from terminal buds, this pest is particularly injurious.
Control of pine tip moth is dependent on proper timing of insecticidal spray applications. In most locations, two to three generations occur each season, with the appropriate application tim frame being mid spring and midsummer. South of the transition zone, a third generation often occurs, and late-summer applications may be required. Acephate, bifenthrin, carbaryl, deltamethrin, permethrin and tebofenozide are among the products labeled for pine tip moth control.
Bagworms — Easy to spot because they use the needles of spruce and juniper to construct their outer woven “bag,” some homeowners have mistaken them for fruit or pine cones. Unfortunately, this case also prevents insecticide applications from effectively contacting the insect.
Bagworms overwinter as eggs within bags fastened to twigs. Eggs hatch late May through mid-June. After hatching, some caterpillars release a streamer of silk and are blown by the wind, establishing new infestations on nearby trees. Others begin to spin their tiny (l/8-inch) protective cases. Bags can grow up to 2 inches in length by the end of the summer.
Bagworm infestations on small trees and shrubs can be controlled by removing bags during the winter and spring before eggs begin to hatch in late spring. Destroy bags by burning, immersing in kerosene or by crushing. If bags containing larvae are discarded on the ground, the larvae can return to host plants.
Chemical controls are most effective if applied while bagworms are still small, usually from mid to late June. A midsummer cleanup application may also be required. Reduced-risk options for controlling bagworms include insecticides containing Bacillus thuringiensis (Bt), spinosad or neem oil (azadirachtin). Insecticidal soaps are also quite effective against young bagworm larvae, but may require repeated applications. These products generally have minimal impact on beneficial insects. Additional insecticide options for bagworm control on ornamental plants include acephate, bifenthrin, chlorantraniliprole, carbaryl, cyfluthrin, dimethoate, esfenvalerate, fluvalinate, lambda-cyhalothrin, permethrin and tebufenozide.
Pine needle scale — Needles of pine are the obvious locations for pine needle scale, which can also infest spruce and fir. Close inspection reveals slender, chalky white flecks about 1/16-inch long. Pine needle scales overwinter as eggs under the old scale of the females. Hatching begins late May or early June, or when new needles begin to appear. Crawlers move to green needles to feed. Scales possess piercing-sucking mouthparts that extract cell sap and desiccate needles.
There are two pine needle scale generations in most locations. When fledgling crawlers emerge from under the waxy covering, they are vulnerable to spray applications. Well-timed applications in late spring and midsummer with horticultural oil (not spruce or fir), insecticidal soap, acephate carbaryl, cyfluthrin, esfenvalerate, fluvalinate, lambda-cyhalothrin or permethrin should achieve good control. Horticultural oil applications can disfigure spruce and fir trees by removing the desirable blue color on the needles.
Pine sawflies — Sawfly larvae resemble caterpillars, but are actually the larvae of primitive wasps. They take on the green to bluish green color of the needles they consume, making them harder to detect. Sawflies have a “herd-like” behavior, feeding gregariously in numbers ranging from 20 to 50 or more, and feeding almost exclusively on one or two-year-old needles.
Tending to be early-season pests, applications are best timed as soon as young larvae appear in early to midspring. Smaller infestations can be controlled simply by using a short stick to knock them off the needles. Once fallen, sawflies do not possess the capacity to reinfest the tree. Heavier infestations can be sprayed with acephate, bifenthrin, carbaryl, cyfluthrin, esfenvalerate, fluvalinate, lambda-cyhalothrin or permethrin.
Spider mites — Even though most of your customers think they are insects, it doesn’t change the fact that mites can cause lots of damage. The first sign of mites is a lackluster appearance of the needles. Spruce and fir tend to be favored hosts. Spruce mites develop in cool, moist weather, building large numbers rapidly. As the stress of summer begins, damage becomes more evident, as they continue to feed.
Once well-established, a fine webbing becomes apparent, which mites use for transport from one needle to another, as well as to protect themselves from predators. As with other needle feeding pests, applications made early in the life cycle are more effective, as extensive webbing can interfere with pesticide contact. The presence of spider mites can be detected by tapping branches over a white piece of paper. Insecticidal soaps, abamectin, acephate, bifenthrin, bifenazate, dicofol, etoxazole and hexythiazox are possible control agents.
Aphids — Both bark and needles are possible locations for pine aphids. Aphids can have multiple generations per year, requiring as little as 35 days each. They are soft-bodied insects with the ability to extract large quantities of cell sap by way of their feeding. Because they are active throughout the growing season, aphids are most certainly a “spray when you see them” insect. Thorough coverage, as well as follow-up treatments, are usually required for acceptable control. Insecticidal soaps, acephate, bifenthrin, cyfluthrin, esfenvalerate, fluvalinate, lambda-cyhalothrin and permethrin are labeled for control of pine aphids. If a serious problem is expected due to past feeding history, imidacloprid soil treatments can also be considered.
Zimmerman pine moth — Easy to see once you know what you’re looking for, Zimmerman pine moth damage is almost always first seen as large masses of whitish, possibly pinkish, pitch. Pine trees grow in whorls, meaning all branches arise from the same location on the stem at various intervals above ground. Pine moth damage is usually located just under the whorls, where the branches attach to the trunk.
In early spring, female moths lay eggs in bark crevices. Soon afterward, young larvae hatch and burrow into the trunk to begin feeding. Once inside, they act like other borer species, creating galleries and tunnels that interfere with water and nutrient transport in the tree. Damaged branches and tops may die or be broken by winds.
The key to Zimmerman pine moth control is timing. It is essential to prevent larvae from boring into the trunk after egg hatch. Because pine moths typically have two generations per year, early spring and late summer applications of bifenthrin or permethrin will help to keep damage to a minimum.