Forest Pests: Insects, Diseases & Other Damage Agents

Pine Bark Beetles Forest Health Guide for Georgia Foresters Written by Terry Price, Georgia Forestry Commission Adapted for the web by the Bugwood Network

(Coleoptera: Dendroctonus species)

The genus Dendroctonus contains the most damaging pine bark beetles in North America. The name Dendroctonus is Latin for “tree killer.” The southern species are listed from top to bottom in Figure 6 - Ips avulsus, Ips grandicollis, Ips calligraphus, Dendroctonus frontalis, and Dendroctonus terebrans. The pine engraver, I. pini (not pictured), occurs in the northern tip of Georgia. It breeds in all species of pine and spruce throughout its range in North America. The southern pine beetle is the most destructive pine bark beetle in the South. Randomly flying females locate susceptible trees, which are called focus trees. Focus trees then become the source of an attracting pheromone called frontalin that attracts other flying beetles. As the focus trees become less attractive due to the male pheromone verbenone, incoming beetles begin to attack neighboring trees. This switching

Figure 6 photo by Gerald J. Lenhard

The SPB attacks all species of southern yellow pines including eastern white pine. It is particularly destructive in overmature and overcrowded stands. Outbreaks are cyclic and are usually preceded by drought or flooding. In non-outbreak years individual spots are often associated with lightning and man caused disturbances.

Trees are killed when thousands of adult beetles bore underneath the bark to feed and lay eggs. The female beetles construct winding S-shaped galleries in the cambium while feeding and laying eggs (Figure 7). Adult beetles carry blue stain fungi and these fungi once introduced into trees will proliferate into the sapwood stopping water movement within the tree. This causes the needles to dry more rapidly. Blue stain can also interfere with southern pine beetle development (Figure 8 - Note the larval galleries terminating at the blue stain border).

Figure 7 photo by Terry Price

Figure 8 photo by Terry Price

The usual signs of attack on the outside of trees will be pitch tubes (in bark crevices when formed) (Figure 9). Other secondary insects such as the southern pine sawyer (Figure 10) and ambrosia beetles will leave their marks behind (Figure 2). Needles will turn pale to yellow green, then red, and then brown. The time required for the needles to fade depends on many factors. Trees attacked during the summer will begin to fade in about two weeks or less, whereas, those attacked in early spring or late fall may not fade for several weeks to months or green needles may shed before they fade in color.

Figure 9 photo by Terry Price

Figure 10 - Pine sawyer egg pit photo by Ronald F. Billings

Several broods are produced per year. Approximately 30-40 days are required for the completion of one brood during the warmer months. During winter all stages (eggs, larvae, pupae, and adults) can be found in trees.

The removal of all infested trees by salvage is the best means of controlling southern pine beetle spots. Another method of control is cut-and-leave. This method involves felling infested trees along with a buffer of uninfested trees and leaving them in the forest. Cut-and-leave disrupts spot growth by interfering with pheromone synchrony. Cut-and-leave should only be considered when salvage removal is prohibited and only during the summer months. Chemical control is used on a very limited basis and is recommended only for spots having fewer than 20 trees. Pile and burn is effective for small spots and for pre-commercial sized trees.

Figure 11 photo by Terry Price

There are two new tactics for controlling southern pine beetles. Phero Tech Inc. has registered a beetle-produced inhibitor, verbenone for use in disrupting spot growth. One tactic uses the verbenone-only and the second includes verbenone-plus-felling.

Southern pine beetle populations can be monitored effectively by deploying pheromone traps in the spring. Traps are baited with the chemical attractant frontalin and gum turpentine (Figure 11). When southern pine beetle catches outnumber those of the predator clerid beetle Thanasimus dubius, southern pine beetle populations are often predicted to increase. The larger the ratio of southern pine beetles to clerids the greater the likelihood of southern pine beetle population growth (Figure 12).

Figure 12 - Adult clerid beetle photo from USDA Forest Service Archives

Aerial detection of southern pine beetle spots is the most effective means of locating spots for salvage. State forestry agencies across the South conduct annual southern pine beetle surveys in order to detect and record spot size and location. Data gathered from the aerial surveys are compiled into a south wide report every 5-6 years. This information is used for regionwide planning and assessment of beetle trends and impacts on timber supply (See Table 1 in Appendix).

Isolated southern pine beetle outbreaks in the Coastal Plain of Georgia historically have been associated with dense, old-growth loblolly and shortleaf pines and less frequently, old-growth slash and longleaf pines on poorly drained sites or in association with flooding. These outbreaks, although local, build rapidly and result in catastrophic losses. Historical information documents the absence of detectable southern pine beetle from many of the Coastal Plain counties in Georgia. However, the current trend to favor loblolly over other less susceptible species in these counties is providing desired habitats for southern pine beetle expansion. Further, with the advent of intensive plantation forestry, the practice of pushing loblolly pine to the limit by increasing stand densities and investing in herbaceous control and fertilization increases the economic losses in the event of a southern pine beetle attack. The spatial rearrangement and enumeration of loblolly pine and the displacement of slash pine in the Coastal Plain may ultimately result in more frequent southern pine beetle outbreaks with greater intensities (See Table 2 in Appendix).

Land managers in the Coastal Plain should consider integrated pest management (IPM) practices aimed at preventing southern pine beetle attacks, especially on marginal sites. These are (1) planting less susceptible species such as slash and/or longleaf pine, (2) reducing planting densities, (3) ripping or subsoiling where appropriate prior to planting, (4) minimizing root deformations at planting, (5) controlling understory competition with prescribe fire and/or herbicides, and (6) accurately timing thinnings to avoid density-related mortality.

Southern pine beetle outbreaks in the Piedmont and Mountain regions of the state are usually preceded by droughts. Piedmont outbreaks occur at 6-10 year intervals and those in the mountains every 12 years. However, many changes in forest structure are occurring in and around urban communities in the state particularly in the Atlanta area and vicinity. Georgia loses about 75,000 acres of forests every year to urban sprawl. The fragmentation of the forest and increased land values has resulted in fewer acres of contiguous pine forests. People are reluctant to invest in forestry when land is valued more for commercial development. Southern pine beetle outbreaks will certainly be impacted by the declining acreage of pine forests. Ips beetles can be distinguished from southern pine beetles by the scooped out shape of their rear ends (Figure 13). I. avulsus completes its life cycle in

Figure 13 - Ips-bottom, southern pine beetle-top photo from USDA Forest Service Archives

Figure 14 - Ips boring dust photo by Terry Price

Figure 15 photo by G. Keith Douce

The small southern pine engraver I. avulsus, prefers the upper portions of trees and is often found in logging slash. The five-spined engraver I. grandicollis, is found more often above mid-bole and will attack logging slash. The six-spined engraver I. calligraphus, is the most aggressive and is found most often in the bottom ½ of trees but during outbreaks can be found in 4” diameter tops. Ips beetles often infest pine stands infected with annosum root rot disease.

Maintaining tree vigor can minimize damage from Ips beetles and salvaging storm damaged trees.

Ips spots are difficult to salvage because they are usually small and scattered making them uneconomical for salvage. Ips outbreaks usually subside after the first season and require no treatment. Exceptions would be places such as yards, golf courses, parks and arboretums.

The black turpentine beetle Dendroctonus terebrans prefers trees damaged by logging and landscaping equipment, naval stores operations and lightning. Outbreaks are also preceded by droughts. During droughts infestations often begin in sawtimber-sized trees in low-lying areas. Attacks are confined to the lower bole and are seldom found more than ten feet off the ground (Figure 16). Pitch tubes are about the size of a quarter and occur in the bark crevices.

Figure 16 photo by Terry Price

Trees damaged during skidding and road building should be treated with a recommended insecticide or removed along with harvest trees. The black turpentine beetle is strongly attracted to the odor of resin that emanates from wounds. Naval stores producers must use insecticides to protect crop trees.

The southern pine coneworm, Dioryctria amatella, produces a pitch tube very similar to the black turpentine beetle but only occurs in conjunction with fusiform rust cankers (Figure 17).

Trees attacked by the black turpentine beetle can be treated effectively with an approved insecticide because it only infests the lower six feet of trunk.

Figure 17 photo by Larry R. Barber

“Frequently Asked Questions About Pine Bark Beetles” How do I know if my trees are currently infested with bark beetles? Trees that still harbor beetles will be characterized by green to yellow needles, tight fitting bark (hard to remove from the tree when struck by a hatchet or ax) and soft gummy pitch tubes. There are exceptions to these and homeowners should seek the advice of a forester to be sure trees are still infested. What are my options for controlling an “active infestation” of Ips and southern pine beetles?

Removal of infested trees is the surest way to get rid of Ips and southern pine beetles. Other options include complete saturation of the entire tree trunk with a recommended insecticide. Trees can be sprayed standing or after being cut and sectioned on the ground. The entire bark area must be sprayed to the point of runoff. Spraying standing trees in urban areas is not generally recommended due to the possibility of pesticide contamination to nearby bird feeders and baths, swimming pools etc.

Another option is to fell trees and chip them on site and spread the chips for mulch. Infested trees should never be cut and stored on site for firewood unless the wood is covered with a plastic or vinyl tarp and sealed along the edges. From April to October infested firewood should be covered for at least 35 days to insure the death of the beetles.

During the cooler months from October to March, infested firewood should remain covered until after dogwoods have bloomed in the spring. Remember, Ips and southern pine beetles can complete a life cycle within 22-30 days respectively and control efforts must be done within this time frame.

What are my options for controlling black turpentine beetle infestations?

The black turpentine beetle is the only pine bark beetle that is confined to the lower six to ten feet of tree trunk. Except in extreme situations, the beetles do not mass attack trees as do the Ips and southern pine beetles. Rather, they tend to build up over a period of weeks thus allowing time for control by homeowners and landowners. Spraying the lower ten feet of trunk with a recommended insecticide can effectively control black turpentine beetles.

Do I need to remove trees that are already dead? (Those with brown needles or no needles.)

Dead trees from which bark beetles have emerged may harbor beneficial insects such as the checkered beetle. If dead trees are no threat to property, humans, or pets, they can be left standing to provide homes for checkered beetles and cavity nesting birds. Be sure dead trees are away from property lines, powerlines, houses, cars and children’s play areas. Stay away from dead trees on windy days as they often lose branches and upper trunk sections from the swaying.

Can I protect my healthy trees with an insecticide before pine beetles get them?

Healthy trees that are near an Ips or southern pine beetle infestation can be protected if the entire trunk area (bottom to top) is treated with a recommended insecticide. This requires expensive equipment capable of thrusting the insecticide up to tree top level. In urban areas where bird baths and feeders, swimming pools, cars and people are often present, spraying standing trees is not a good idea. Although it’s effective in preventing bark beetle attacks, it is often impractical.

Many tree companies offer to spray standing pines up to a height of about ten feet. This is only effective against the black turpentine beetle and will not provide protection against Ips and southern pine beetles. Also, many tree companies advertise the injection of systemic chemicals to control or prevent bark beetles. Although the Environmental Protection Agency (EPA) has allowed the registration of systemic insecticides for control of pine bark beetles, their effectiveness is often contraindicated. Stay with the proven methods even though they may be more costly and labor intensive.

Will chips from recently ground pine trees attract pine beetles to my yard?

Yes and no! The black turpentine beetle is justly named because it is highly attracted to the odor of fresh pine tree resin. Sometimes green pine chips may heighten the possibility of a black turpentine beetle attack and to a lesser extent attacks from the other bark beetles. To be safe, pine chips should be used only in and around hardwood areas.

Must I have the stumps ground when I remove an infested tree?

Black turpentine beetles like the smell of fresh pine resin and a green stump is a prime target for them. Stump grinding is preferred when green pines are cut. If not, the stumps should be sprayed with a recommended insecticide unless there are no more pines left in the yard.

Does pruning attract pine bark beetles?

It is best to prune pine trees when pine beetles are inactive. Pruning trees between November and February is preferred to spring and summer pruning. If pruning can’t be postponed, the pruning wounds should be coated with a tree wound dressing to reduce the possibility of a bark beetle attack.

Climbing spurs used by many tree surgeons and arborists when pruning can attract pine beetles. If pine beetles are on the rampage it is best to delay any pruning until the outbreak subsides. This would apply to powerline pruning as well.

What should I do if my neighbor has trees infested with pine bark beetles?

It is always a good practice to be aware of bark beetle activity or tree lightning strikes in your neighborhood or area. Pine bark beetles can devastate neighborhoods or woodlands and do not respect property lines. Quick action to rid an area of beetles is a must. Be sure your neighbors are aware of the situation.

What are my responsibilities toward my neighbors if I have an active bark beetle infestation on my property?

Once you have been educated to the potential hazard of your infestation spreading to nearby properties, you may be liable for negligence by failing to remove the beetle hazard(s). Neighbors need to work together to solve a community problem.

Are there any federal and state tax relief options for homeowners and timber owners plagued by pine bark beetles?

Yes! The IRS recognizes the southern pine beetle as a casualty agent. This means homeowners can minimize losses provided they document and report the losses in an appropriate manner approved by the IRS. Generally, homeowners can have the property appraised with and without the trees (those killed by beetles). The depreciation in property value due to missing trees is the amount of the casualty allowed by the IRS. Timber growers may qualify for an involuntary conversion. Under this rule, landowners who salvage killed trees may be able to reinvest the income into “like-kind” property within 3 years and postpone taxes.

Homeowners and timber owners need to refer to IRS publication 547, Casualties, Disasters and Thefts. This publication is available free of charge by calling 1-800-TAX-FORM.

What type of assistance does the Georgia Forestry Commission provide to homeowners in dealing with pine bark beetles?

The Georgia Forestry Commission provides technical assistance to any homeowner/landowner or neighborhood association upon request. During community wide or statewide beetle outbreaks, a GFC representative can provide a program to citizens about how to recognize and control pine bark beetles. It can also publicize and coordinate community wide suppression activities by training various tree companies, arborists and timber harvesters on proper control procedures. As a state agency the GFC does not remove trees nor provide financial assistance to citizens for tree removal. Contact the Georgia Forestry Commission by calling your local county office or 1-800-GA TREES or go online at www.gatrees.org

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