Forest Pests: Insects, Diseases & Other Damage Agents

Southern Pine Beetle - Dendroctonus frontalis Georgia Forestry Commission Forest Health Monitoring Factsheets Written by Terry Price, Georgia Forestry Commission Adapted for the web by the Bugwood Network

The southern pine beetle is the most destructive pine bark beetle in the South. In Georgia alone, it kills an estimated $7.5 million worth of trees each year. Widespread outbreaks occur at predictable intervals and are preceded by drought or flooding depending on the region of the State. Spots of killed trees may range in size from a few trees to several thousand (Figure 1). It has been estimated that a single pine tree eight inches in diameter and 50 feet tall can produce over 125,000 beetles.

Figure 1 photo by Ronald F. Billings

All species of southern pines are attacked during outbreaks but shortleaf and loblolly are preferred when populations are low and scattered. When beetle numbers are low, weakened trees are preferred because vigorous, fast growing trees can oftentimes "pitch out" attacking beetles. Trees weakened or damaged by lightning or overcrowding, root diseases caused by Heterobasidion annosum or Leptographium spp. serve as focal points for new infestations. A relatively new phenomenon known as loblolly pine decline (LPD) is stimulating a lot of interest into hazard rating stands for susceptibility to southern pine beetles. LPD results from the debilitation of the tree's root system by Leptographium spp. High Leptographium incidence has been statistically related to decreased resin flow, poor root condition, reduced radial growth and thin crowns all of which increases the susceptibility to southern pine beetle attack.

The southern pine beetle kills the tree by girdling in the cambium layer (Figure 2) and by introducing blue-stain fungi that clog water-conducting tissues within the tree (Figure 3). Pitch tubes and boring dust are formed on the tree trunk indicating the points of entry of attacking females (Figure 4). Other signs indicating a southern pine beetle attack will be sawdust around the tree's base caused by ambrosia beetles (Figure 5), fading treetops (Figure 6) and egg laying pits caused by a secondary insect known as the southern pine sawyer (Figure 7).

Figure 2 photo by Ronald F. Billings	Figure 3 photo by Ronald F. Billings
Figure 4 photo by Erich G. Vallery	Figure 5 photo by Ronald F. Billings
Figure 6 photo by Andrew J. Boone	Figure 7 photo by Lacy L. Hyche

Southern pine beetles are very small (Figure 8) but are capable of flying good distances and will attack trees from as low as 5 feet upward to mid crown. The first attacks occur usually at 10 feet to mid bole with subsequent attacks concentrating on other portions of the stem. After about a week, most of the main stem is infested. Southern pine beetles are dormant during the winter months, except for warm periods, and become active in the spring at about the time dogwoods are blooming. From this point on, a new brood of beetles is produced at 30-day intervals until the weather begins to cool in late October to early November.

Figure 8 photo by Erich G. Vallery

Preventing southern pine beetle infestations can be accomplished by reducing those factors that weaken trees. Pine stands should not be allowed to stagnate. Stands should be thinned before crown closure and stand densities should be maintained at or below 80 sq. ft. of basal area per acre. Planting densities should be kept to a minimum (< 550 trees per acre) to prevent overcrowding early on.

Loblolly, shortleaf and Virginia pines are the most susceptible species to southern pine beetles. When practical, other species of pines that are more resistant to attack should be planted. The Mountain or Montane variety of longleaf pine has been planted in several field trials in Jones, Jasper and Spalding counties Georgia. Early results indicate the tree survives well on clay sites and releases from the grass stage as early as the end of the second growing season (Figure 9). The GFC maintains these field demonstrations of longleaf pine and landowners interested in viewing them can contact the GFC at 1-800-GA TREES or the Brender Demonstration Forest at 1-478-986-3914.

Figure 9 photo by David Stephens

Prescribed fire can increase stand vigor by eliminating hardwood competition but fire used improperly can create conditions favorable for Leptographium spp. of root pathogens. Roots damaged by fire are susceptible to feeding by several species of pine weevils and Hylastes spp. of beetles. These insects are transmitters of Leptographium species of fungi that have recently been associated with loblolly pine decline.

Southern pine beetle infestations in woodlots can be controlled by several methods but all require knowledge of the beetles' life cycle and the ability to identify infested trees. The southern pine beetle uses a very sophisticated system of communication. Attacking female beetles release a chemical attractant (pheromone) called frontalin which signals male beetles to the area. After the males arrive and mating has occurred, the male beetles release an odor called verbenone that signals other incoming beetles to switch to other surrounding trees that have not been attacked. This switching mechanism is responsible for spot growth. Before a spot can be controlled one must determine the direction of movement (Figure 10). Some spots will be expanding in several directions (Figure 11), while most will be growing in the general direction of wind movement. This is due in part to the chemical attractant being dispersed by the wind.

Figure 10 photo from USDA Forest Service Archives

Figure 11 photo by Tim Tigner

As figure 10 illustrates, the arrow denotes the direction of movement of the spot. This area is referred to as the active head. The active head contains all of the trees currently under attack as well as a buffer strip of green uninfested trees. In order to control this spot, the salvage operator must begin cutting the trees in the buffer strip and active head (fading green and green topped trees) first. The older killed trees (trees with red needles or with no needles remaining) should be removed last. The buffer of green trees should include trees within a distance of 100-200 feet beyond the last identifiable infested tree. There is nothing magical about the width of the buffer strip. It may vary depending on the stand density and the rate of growth from incoming beetles. In some instances entire stands must be clearcut in order to contain the beetles and recover economic losses.

Another method of control in forests is called cut and leave. This technique is only recommended when salvage cannot be carried out. Cut and leave is effective in stopping or impeding spot growth from May until the weather begins to cool in early fall (usually September). A forester should be consulted with before cut and leave is chosen as a control method.

Bifenthrin insecticide (Onyx®) is registered for prevention or control of the southern pine beetle in yard trees but not for forest trees. Bifenthrin is a synthetic pyrethroid insecticide and is one of the newest products on the market. It is more stable than the other pyrethroid insecticides and provides effective control for several months. The use of bifenthrin should be restricted to small spots. Remember! Spray only the infested trees. Again you may need to consult with a forester for assistance in deciding which method of control is best in a particular situation.

The Internal Revenue Service (IRS) recognizes the southern pine beetle as a casualty in urban or yard tree settings. This means homeowners can recover some of their loss provided they document and report the losses in an appropriate manner approved by the IRS. Timber growers who have lost trees to the southern pine beetle 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. For more information refer to IRS publication 547, Casualties, Disasters and Thefts. This publication is available free of charge by calling 1-800-TAX FORM.

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