A Guide to Common Forest Pests in Georgia
Pine Bark Beetles
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).
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.
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.