A Guide to Common Forest Pests in Georgia

Terry Price, Forest Health Specialist, Georgia Forestry Commission

Pine Bark Beetles

Pine bark beetles are the most destructive insects of pines in Georgia. They occur across all land ownership patterns and geographic regions of the State. Since 1962 annual losses from outbreaks have exceeded five million dollars in the State. Six species occur in Georgia but only five are of economic importance (Figure 1).

Records of southern pine beetle (SPB) outbreaks in Georgia go back as early as the 1700's. Statewide outbreaks occur every 5-10 years with local, less intense infestations occuring annually.

Ips and black turpentine beetle (BTB) outbreaks seem to coincide with droughts, logging activities, naval stores, or wildfires. It is not uncommon for these insects to increase as SPB outbreaks decline.

Aerial detection is the most efficient method of locating hark beetle spots. Large forested areas can be surveyed in a relatively short period of time. From the airspots can be classified by size and type, which will aid entomologists in predicting future trends. Many small (5-10 trees) scattered spots usually indicate the beginning of a serious outbreak. As the outbreak progresses, spot size may increase 10-50 fold (Figure 2). Aerial detection and suppression surveys are an important aspect of a bark beetle prevention and control program.

Southern Pine Beetle - This beetle attacks all species of southern yellow pines of sapling, pulpwood and sawtimber size. It is particularly destructive in overmature and overcrowded stands. Infestations are often caused by extended droughts, flooding, lightning strikes, and man caused disturbances. Adult beetles are about 3/32" in length and reddish brown to black (Figure 1). Trees are killed when thousands of adult beetles bore underneath the bark to feed and lay eggs (Figure 3). Blue staining fungi are carried on the beetles' bodies from tree to tree. These fungi once introduced into trees will proliferate into the water conducting tissues stopping sap movement within the tree (Figure 4). This causes the needles to dry more rapidly.

Signs of attacks on the outside of the tree will be pitch tubes and boring dust (Figure 5 and 6). Needles will turn a pale to yellow green, then red, then brown (Figure 7). The time required for the needles to begin fading after an attack depends on many factors. Trees attacked during the summer will begin to fade in about two weeks, whereas, those attacked in early spring or late fall may not turn color for several weeks to months.

The SPR produces several broods per year. Approximately 30-40 days are required for the completion of one brood during the warmer months. During the winter all stages (eggs, larvae, pupae, and adults) can be found under or in the bark of infested trees.

Control In Forest Stands - After an SPB spot has been detected from the air, it must be ground checked. Recently attacked trees will have green needles and cannot be seen from the air, therefore, a spot may appear from the air to consist of only a few affected trees. A closer examination on the ground may reveal 10 or more green topped, infested trees for every discolored tree.

Currently four methods of control are being recommended in Georgia. These are salvage, cut and leave, cut and spray, and pile and burn. Another method which involves the use of behavioral chemicals is being tested throughout the south. Based on preliminary results this method may prove to be an alternative in controlling small isolated spots.

Salvage is the removal of all infested trees along with a buffer strip of green uninfested trees. It is the most practical and effective method of control when the demand for timber is good. Salvage is not effective when:

  •   Spots are inaccessible to logging equipment.
  •   Spots are too small to be harvested economically.
  •   Wood quotas restrain the movement of wood.
  •   There is a shortage of wood producers.
  •   When salvage is impractical cut and leave is   recommended as an alternative.

Cut and leave is the felling of all infested trees, plus a buffer of uninfested trees toward the spot center and leaving them. This method has been shown to disrupt spot growth during the warmer months (May-September) but should not be used on spots having over 50-100 infested trees.

Chemical control is used on a very limited basis and is recommended only for spots having fewer than 20 trees. The chemicals that are registered for bark beetle control are restricted use pesticides and can be applied only by licensed pesticide applicators (see appendix).

Pile and burn is an effective control method for small spots but is seldom used because of the time and expense involved in doing it.

If pre-commercial stands become infested, good control can be achieved by knocking all the trees down and burning.

Figure 1 - The Southern pine bark beetles. Top to bottom:. Ips avulsus, Ips grandicollis, Ips calligraphus, Dendroctonus frontalis (SPB) and Dendroctonus terebrans (BTB).
Photo by Gerald Lenhard, LSU

Figure 2 - A Southern Pine Beetle infestation
Photo by Terry Price, GFC

Figure 3 - Southern Pine Beetle egg galleries and larvae
Photo by Terry Price, GFC

Figure 4 - Cross-section of a blue stain infested log
Photo by James McGraw, NC State

Figure 5 - Southern Pine Beetle pitch tubes
Photo by Terry Price, GFC

Figure 6 - Bark beetle boring dust
Photo by Terry Price, GFC

Figure 7 - Southern Pine Beetle infestation showing the different stages of needle fade
Photo by Terry Price, GFC

Figure 8 - Attacks from SPB and Ips engravers can be prevented in standing trees by applying the insecticide to the entire outer bark surface. However, trees already infested cannot be saved by spraying and should be removed/
Photo by UGA Archives

Figure 9a - Ips larvae feed out in a fan pattern away from the adult gallery
Photo by USFS Archives

Figure 9b - Adult Ips egg galleries
Photo by USFS Archives

Control In Lawn and Shade Trees - Trees that have been mass attacked by southern pine beetles cannot be saved by the application of an insecticide to the outside bark or by injecting it into the tree. Homeowners need to be aware of unscrupulous persons advocating the use of systemic chemicals for the control of any pine bark beetle. Research has yet to prove the efficacy of these compounds.

The most important step in stopping a beetle infestation in a yard is to remove all infested trees. Residual healthy trees can be protected by the application of an approved insecticide to the entire outer bark surface of the trunk (Figure 8). Tree companies are often limited by their spray equipment and can only spray up the tree about 15 feet. This will not be effective in preventing attacks from the southern pine beetle or Ips engravers.

Lightning struck pines should he removed as soon as possible to avoid a southern pine beetle or any other bark beetle problem.

Preventing Beetle Attacks In Pine Stands - Dense stocking results in reduced diameter growth and creates conditions favorable to beetle infestations. Thinning stimulates growth and vigor in young stands and reduces the chances of a beetle infestation. Stands should he thinned at the onset of competition. Thinning intensity will depend upon the age of the stand, site index, total stand density, management obiectives andl the area of the state. In Georgia basal areas of 80 to 100 feet square per acre are recommended to reduce the potential for a beetle attack. Pine stands in the northern half of Georgia are susceptible to ice damage if thinned too heavily. Spacing trees around 600 per acre at establishment will reduce the number of thinnings required thus lessening the effects of ice.

Damage from recent logging activities favors all of the bark beetles. Skinned trees next to skid trails, logging roads and loading decks should be removed.

Susceptibility of trees to beetle attacks increases with age and causesa marked decline in diameter growth. Mature and overmature trees seldom respond to thinnings and should be replaced with the most resistant pine species or a species mixture suited to the site. Pine rotations should be shortened in areas where beetles have historically caused considerable timber losses.

Ips Engraver Beetles

These beetles can multiply rapidly in fire or storm damaged timber, in logging slash or along powerlines in recently pruned pines. Duration of Ips outbreaks is usually short-lived (3-6 months), and they are not as widespread as SPB outbreaks. Trees attacked by SPB are often attacked by one or more species of Ips. The Ips engravers tunnel underneath the bark of living trees producing galleries that are characteristic of each species (Figure 9). Blue staining fungi are also introduced into trees by the Ips.

The small southern pine engraver prefers the upper portions of trees such as limbs and tops and is often found in logging slash. The five-spined southern pine engraver is found more often above mid-hole and will also attack logging slash. The six-spined engraver is found most frequently in the bottom 1/2 of trees but during outbreaks it can be found in 4" diameter tops.

Ips beetles can be distinguished from other bark beetles by the shape of their rear ends, which are scooped out and surrounded by blunt spines (Figure 1).

The smallest Ips completes its life cycle in about 20 days during warm weather and may produce ten or more generations per year. The 5- and 6-spined engravers develop over a 20-25 day period producing 6 or more generations per year.

Trees attacked by Ips beetles don't always produce pitch tubes. Reddish-brown boring dust is produced and will be sprinkled up and down the tree in the bark crevices (Figure 6).

Damage from Ips beetles can be minimized in forest stands by maintaining tree vigor, delaying thinnings during droughts and/or outbreak years, and rapidly salvaging storm damaged trees. All thinnings should be continuous with as much of the tops being utilized as possible. If thinning operations are started and then delayed, the beetles emerging from the logging slash will be more likely to attack standing trees. A continuous thinning provides fresh slash that tends to keep the beetles away from standing trees. Limbgating operations tend to favor Ips' buildups. The limbs are piled in heaps and do not dry out as fast as they should. The piles should be scattered periodically to allow for drying.

During droughts, aerial surveys should be intensified in areas where Ips have historically been a problem.

Ips outbreaks in recreational and urban areas can be devastating in overmature trees. During the summer of 1980 the 4 and 6 spined Ips killed over 30,000 board feet of shortleaf and loblolly pines along the fairways of an 18-hole golf course. This particular local outbreak was started by a few lightning strikes. It was intensified by drought. Statewide, Ips outbreaks accounted for 12,000 cords and over 490,000 bd. ft. of timber being salvaged during 1980.

Trees can be protected from Ips attacks by spraying the entire trunks of trees (Figure 8). The same insecticides that are recommended for the SPB are also registered for use against Ips beetles (see appendix).

Black Turpentine Beetle

This beetle is found most frequently in trees damaged by logging and landscaping equipment, naval stores operations, and lightning. Outbreaks are also triggered by droughts. During droughts, infestations often appear in sawtimber sized trees in low lying areas. Pulpwood and sawtimber sized trees of all ages are attacked.

Trees attacked by black turpentine beetles will have pinkish-white globs of gum on the bottom 6 feet of trunk (Figure 10). Pinkish-white boring particles also accumulate at the base of trees. Kicking back the duff layer from around the trees base will expose the boring particles.

The adult beetles tunnel underneath the bark and construct a broad vertical gallery in the cambium. Eggs are laid in clusters along the sides of the gallery (Figure 11). Development is completed over a 70-80 day period during the warmer months.

Trees damaged during skidding and road building should be removed along with scheduled removals. Black turpentine beetles are highly attracted to the turpentine odor that emanates from tree wounds. Wounded trees are almost certain to be attacked.

Figure 10 - Black Turpentine Beetle pitch tubes
Photo by Terry Price, GFC

Figure 11 - Black Turpentine Beetle adults with egg mass
Photo by Terry Price, GFC

Insecticides can be used to prevent or control attacks by this beetle. In naval stores operations trees should be sprayed prior to being chipped. Field experiments have demonstrated the effectiveness of lindane/water emulsion sprays in preventing beetle attacks on naval stores trees. Yard trees damaged by bulldozers or other heavy equipment should be sprayed soon after the damage occurs to prevent these beetles from attacking. Prevention is always a better approach than control.

Ambrosia Beetles

There are many species of ambrosia beetles that attack hardwood and coniferous trees. Ambrosia beetles are so named because they cultivate a mold type fungus in their galleries, upon which they feed. Some species attack green logs, dying trees, or twigs and branches of living trees (Figure 12).

The species that attack logs and dying trees can cause considerable degradation in lumber. The beetles damage the wood by boring uniform circular pin holes through the wood. The fungus they cultivate causes black stains throughout the wood which further causes degradation (Figure 13). Ambrosia beetle tunnels also provide entrances for certain wood rot fungi which can do serious damage in untreated wood. Logs should be removed from the forest and utilized as soon as possible to prevent attacks from the pin hole borers.

The species attacking twigs and branches of living trees can cause extensive dieback, particularly in weakened trees. These beetles carry species of fungi on their bodies that are capable of causing tree mortality. The black twig borer, Xylosandrus compactus, has recently been associated with branch dieback on transplanted laurel and live oaks. A Fusarium spp. was isolated from dead and dying twigs and branches taken from trees that had been attacked by the beetles. This beetle is expected to become a serious pest of hardwood trees in areas where it becomes established. In Georgia it has been associated with dieback on holly, magnolia and various oak species.

Attacked twigs and branches should be pruned and destroyed. Trees should be watered during dry periods. Recently transplanted trees are very susceptible to black twig borer attacks. To minimize susceptibility don't transplant stock over 3-4 inches in diameter at the ground. Severe damage and death has occurred when larger trees are transplanted.

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