As a group, pines are versatile and appealing, and as such can become important plants in the landscape. Unfortunately, pines are often plagued by a number of damaging insects and related pests. Several insect species have great capacity to cause harm and limit the function and aesthetics of pines, while others are much less damaging.

As tree care providers, your job is to sift through all available information and design a control program that is soft on the environment yet effective at achieving the goal of limiting infestations sufficiently to keep plants thriving in the landscape. Strategies for best landscape management practices follow.

Regardless of which insect pest species is being considered, thorough inspection must be at the heart of any management effort. A hallmark of integrated pest management (IPM), regular and thorough inspection provides at least two significant benefits for the tree service provider.

The first involves the facilitation and implementation of the best tree care available, at least from a pest control standpoint. Trees under the care of a provider who employs regular inspections as a central tenet of their IPM program treat only when it’s needed. The authors are aware of several recent instances where pines, spruce and fir have been treated on a predetermined “just because they’re a conifer” basis, rather than on a justified need for control. Spray applications made under these circumstances border on fraud.

The second benefit involves the creation of an enhanced profit center and income stream based on the individual arborist’s training, experience and knowledge instead of how much product was sprayed on a tree. Approaches to insect control based on reputation or “guilt by association” are profitable because property owners can be convinced that previously noninfested trees must be protected. Sure, these applications are effective, but the same application using only water would also be effective if insect pests are not actually present at the time of application or a history of previous infestation has not been established.

The arborist should develop a protocol whereby a customer’s property is thoroughly inspected (monthly is a good time frame) for the presence of insect and mite pests and their symptoms of damage. Here’s the good part — after each inspection, just like after each spray application, send the customer an invoice for the time spent examining trees. Of course, if insect pests are detected, appropriate applications can be scheduled according to the most efficacious product and timing for each species.

There are two approaches that can be used for conducting landscape inspections. The first is a “walk and talk” with the customer. These tend to be more time consuming, but provide a great opportunity to schmooze with the customer and stress the importance of your services. The second method is to inspect on your own and report the findings later in a simple report format. The second approach is usually faster and better for training new employees, but tends to leave interested clients out of the loop. Certainly, a bit of discretion is a key consideration for each approach.

The following are some of the more important pests of conifers:

1. Mountain pine beetle

A major pest of pines in the western U.S., mountain pine beetles commonly damage ponderosa, lodgepole, Scotch and limber pines. As with many other insect pests, damage during the early stages of an infestation tends to be limited to trees already under stress from poorly developed root systems, drought, competition or other injuries. As infestations become larger and larger, damage often becomes apparent in trees in close proximity to the initial infestation.

Damage from mountain pine beetles. Photo: James A. Kalisch

The signs and symptoms of an infestation are characterized by irregularly shaped, marble-sized masses of resin, or “pitch tubes,” which may be white, brown or pink in color. These masses are caused by insects tunneling under the bark. In many cases, woodpeckers can be seen foraging on infested trees. After a tree has been attacked and beetles have been feeding for a growing season, the tree crown becomes visibly affected, turning reddish or yellow in color. The most reliable indicator of a mountain pine beetle infestation is the presence of live insects in their various life stages: eggs, larvae, pupae or adults. A small axe or hatchet is useful when examining trees.

Control of mountain pine beetles is largely preventive in nature. Once an infestation is present, control attempts usually fail. Because dense plantings of pine are more susceptible to mountain pine beetle than properly spaced stands or landscapes, removal of weak trees will improve the effectiveness of control attempts. Additionally, timely applications of carbaryl, bifenthrin or permethrin to individual trees of high value may provide some level of control. These sprays must be applied before the flight of the beetles begins.

Mountain pine beetles. Photo: USDA Forest Service

2. Pine sawyer beetle

Known for its role in facilitating the spread of pine wilt disease, pine sawyer beetles are best thought of as carriers or vectors. During feeding on healthy pine trees, nematodes carried in the beetle’s respiratory system enter the tree via wounds created by beetle feeding activity.

This mode of transmission of the killing agent (nematodes) is not dissimilar from how another devastating tree malady, Dutch elm disease, which is caused by a fungus is spread.

Mature larva of the pine sawyer beetle. Photo: James A. Kalisch

Adults (beetles) are attracted to recently dead or dying trees. Egg laying takes place in crevices in the bark after feeding. After eggs hatch, the larvae feed for several weeks in the cambium layer before boring into the sapwood of the tree branches and trunk. While larval feeding is certainly damaging to pine trees, it is not nearly as disruptive of the nutrient and water flow as the damage caused by the presence of the transferred nematodes.

Effective control of pine sawyer beetles and the associated pine wilt disease is difficult and necessitates multiple strategies. The first involves not planting susceptible pine species such as Scotch, and red and black Japanese. Secondly, removal of symptomatic trees will usually help limit the spread of the disease. Burning the wood from infested trees is also recommended. A third strategy involves landscape and windbreak designs that include a variety of pine and other conifer species instead of monocultures. This approach improves the genetic resistance of the overall landscape and should be implemented wherever feasible. Finally, in certain instances, especially where high-value or sentimental trees are in place, limited success has been achieved with frequent applications of bifenthrin or permethrin applied to the foliage and bark of susceptible specimens. Four to five applications per year are usually required in these situations. Research is underway to determine if insecticide injections are effective as well.

Pine sawyer damage on ponderosa pine. Photo: James A. Kalisch

3. 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 in length. Pine needle scales overwinter as eggs under the old scale of the females. Hatching begins in late spring or early summer when new needles begin to appear. Crawlers move to green needles to feed. Scales possess piercing-sucking mouthparts used to extract cell sap, which desiccates the needles.

There are two pine needle scale generations per year 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 on spruce or fir), insecticidal soap, acephate, carbaryl, cyfluthrin, esfenvalerate, fluvalinate, lambda-cyhalothrin or permethrin should provide excellent control. Use caution when applying horticultural oils because they can blemish spruce and fir trees by removing the needles’ desirable blue color.

4. Pine sawflies

Sawfly larvae resemble caterpillars, but are actually the larvae of primitive wasps. Sawflies 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. Most species feed almost exclusively on one or two-year-old needles.

Pine sawflies are generally early-season pests, so insecticide applications are best timed to control young larvae in early to midspring. Smaller infestations can be controlled simply by using a short stick to knock them off needles. Once on the ground, sawflies do not possess the capacity to re-infest the tree. Heavier infestations can be sprayed with products containing acephate, bifenthrin, carbaryl, cyfluthrin, esfenvalerate, fluvalinate, lambda-cyhalothrin or permethrin.

5. Zimmerman pine moth

Zimmerman pine moth damage is usually spotted first as large masses of whitish or 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.

Zimmerman pine moth. Photo: James A. Kalisch

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 any 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 newly hatched 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 should help to keep damage to a minimum.