Southern Pine Beetles Can Kill Your Ornamental Pine
Robert C. Thatcher - Program Manager,
Jack E. Coster - Applications Coordinator, and
Thomas L. Payne - Research Coordinator,
Southern Pine Beetle Program, Pineville, LA.
Pine Bark Beetles - A Forest Menace
Southern pine beetles are compulsive eaters. Each year in the South from Texas to Virginia the voracious insects conduct a movable feast across thousands of acres of pine forests. Most trees die soon after the beetles sink their teeth into them (Fig. 1).
And hungry beetles are hard to stop. In the early 1970's, they killed pines containing enough board feet of lumber to build about 55,000 new houses. Less than half of this wood was removed from the forest and used.
|Figure 1. - Red-topped
trees killed by beetles.
And They Can Be a Menace To You, Too
Unless you are a forest manager or work in the woods, you may not know just how much damage the beetles can do. Normally, they remain under the bark of pine trees back in the forest, silently gnawing away at a healthy chunk of the southern timber supply.
But not always. Sometimes they forage across forest lines and onto suburban or urban lots and yards (Fig. 2). The homeowner with pines is not out of the woods as far as southern pine beetles are concerned. For this reason, owners of ornamental pines in the South should learn how to recognize and cope with bark beetle attacks.
|Figure 2. - Newly killed pines
around surburban home.
Appearance and Life Cycle
|Figure 3A. - Life stages of the
southern pine beetle - egg.
|Figure 3B. - Life stages of the
southern pine beetle - larval.
|Figure 3C. - Life stages of the
southern pine beetle - pupa.
|Figure 3D. - Life stages of the
southern pine beetle - adult.
Adult southern pine beetles are roughly 1/8 inch long, which is about the size of a grain of rice, and reddish brown to solid black. The insect goes through four life stages - egg, larva, pupa, and adult (Fig. 3) - in the inner bark of its host pine tree.
Eggs are mere pearly white dots. Larvae, or "grubs," are white, legless, and crescent shaped, with glossy reddish-brown heads. Pupae are also white but closely resemble the adult beetle shape.
Beetles mature in about a month and three to eight generations are born each year. Adults have wings; after killing the tree in which they were born, the beetles fly to another living pine to start the life cycle again.
How Beetles Kill Pines
Southern pine beetles may feast on a tree by themselves, or they may have company - three species of Ips engraver beetles and black turpentine beetles. The different species sometimes strike at the same time, making it hard to tell precisely what role each species plays in killing the pine and how much they help or hinder each other (Fig. 4).
There are three sizes of Ips engraver beetles. The smallest is slightly smaller than the southern pine beetle and attacks the upper part of the pine, including high branches. Middle-sized Ips prefer the midsection and upper level of the trunk, while the large engravers seem to favor the lower onethird. Although they can wipe out an entire stand of pines if conditions are conductive to beetle spread, all species of Ips usually kill only one or a few pines in isolated outbreaks.
|Figure 4. - Major pine bark beetles of the South
and the trunk areas usually attacked. From top to
bottom: small Ips, medium Ips, large Ips, southern
pine beetle, and black turpentine beetle.
The black turpentine beetle is the largest bark beetle in the South, about 1/4 inch long. Yet it is the least destructive because it attacks in smaller numbers, strikes fewer trees, and takes longer to kill them than the other species do. The black turpentine beetle likes the lower third of very weak or dying pines and will even make a home for itself in freshly cut stumps.
Southern pine beetles can kill a pine tree in a matter of days. Thousands of winged adults attack a single tree, bore through the bark, and hollow out egg "galleries." The females lay eggs in niches beside the galleries. In a week or so, larvae hatch and start chewing their way through the cambium - living conductive tissue - around the tree. This feeding "girdles" the pine and cuts off the normal flow of moisture and nutrients throughout the tree's system, quickly sapping its strength and contributing to its death. Adult feeding and a blue-stain fungus, which piggybacks its way inside pine bark on attacking adult beetles, help bring on tree death.
Symptoms of Beetle Attack
Successful attacks by southern pine beetles or by more than one species of Ips engravers always kill the tree. But if you act quickly enough, your pines can weather attacks by black turpentine beetles. Because control measures depend in part on whether or not the tree can be saved, you must first identify the species of beetle you are dealing with.
First signs of southern pine beetle attacks are popcorn-size lumps of pitch, called "pitch tubes," which occur at heights up to 60 feet (Fig. 5). The pitch tubes of black turpentine beetles are much larger - and appear at the foot of the tree (Fig. 6). Ips beetles rarely leave pitch tubes. During dry weather, pitch tubes do not appear; instead, red boring dust, which looks like fine red sawdust, will collect in bark crevices and at the base of the pine.
|Figure 5. - Pitch tubes, the first sign
of southern pine beetle attack.
|Figure 6. - The pitch tubes of black
turpentine beetles are larger and lower than
those of southern pine and Ips beetles.
|Figure 7. - Beetles chew galleries
in the inner bark of pines.
|Figure 8. - Needles on trees killed by beetles fade from green to yellow, red, and brown.|
In later stages of southern pine beetle attack, you will be able to see small S-shaped feeding cuts on the inside of the bark (Fig. 7). Black turpentine beetles make vertical, wide etchings and Ips cut either Y- or H-shaped tunnels. The final sign of attack - and the sure mark of death for the tree - is a fade in needle color form green to yellow, red, and brown (Fig. 8).
Pines Likely to be Attacked
Some trees are apparently more appetizing to southern pine beetles than other trees. For instance, beetles seem to prefer loblolly, shortleaf, and Virginia pines to other kinds. During a beetle population explosion, however, the insects will take any species of pine available.
And old, unhealthy, or weakened pines of all species - whether diseased, damaged, or otherwise stressed - can be sitting ducks for southern pine beetles. Such trees have limited supplies of pitch, which is a tree's best natural defense against wood-boring insects.
| Healthy pines can sometimes "pitch out" beetle attacks by entrapping or smothering the invaders with a heavy and prolonged flow of pitch. Sick ones cannot (Fig. 9).
What weakens pines? Natural causes like old age, drought, prolonged floods, hard freezes, fire, and lightning strikes can undermine your pine's vigor and make it more vulnerable to beetles (Fig. 10). The same is true of diseases such as littleleaf and fungus-caused root rot.
Man, too, causes problems. Common landscaping operations like bulldozing and road grating may inadvertently pave the way for beetles by damaging tree roots and trunks (Fig. 11). Heavy traffic by trucks and other construction equipment during the building of a new house often packs down the soil around tree roots. This hurts the pine because it prevents normal movement of water and air through the root zone (Figs. 12 and 13).
|Figure 9. - A healthy pine can
sometimes pitch out beetle attacks.
|Figure 10. - Beetles often attack
|Figure 11. - A pine that has been
gouged by heavy equiptment.
|Figure 12. - Construction work has disturbed
this soil and skinned bark from the trees.
|Figure 13. - Laying sewer or water lines
can disturb soil and weaken pines.
What You Can Do to Prevent Beetle Attacks
The best way to protect your pine trees is to make sure they are not attacked in the first place. Keep them healthy. Remember, a wounded, sick, or lightening-struck pine on your lawn is a standing invitation to dinner for southern pine beetles.
But the beetles' preference for sick or weak trees does not mean they cannot or will not kill healthy pines. They often do. In fact, once the bugs have built up a large population, not even the strongest and healthiest pines can fight them off. This is why a single damaged or unhealthy pine in your neighborhood - which the beetles can use as a place to get started - endangers all the rest, sick or healthy (Fig. 14).
If you are building a new house, keep the soil form being packed down or piled up on tree roots. This will help prevent drastic changes in ground water movement. Avoid leaving only old, large pines on your land, since these trees are prime targets for beetles. In warm weather during the construction period check every few days for pitch tubes on the outer bark of your trees.
On older, established lawns, you should water pines during dry spells and fertilize them as needed. As a general rule, two pounds of fertilizer - such as 10-8-6 formula - for each inch of tree diameter will be enough supplemental nutrition for mature pines. For younger trees of less then 6 inches in diameter, use only one pound of fertilizer per inch of diameter. For soil analysis and more complete details on fertilizing your pines, check with your county extension agent (Fig. 15).
|Figure 14. - This old, diseased tree
jeopardizes the healthy ones next to it.
|Figure 15. - Beetles may attack
healthy pines on established lawns.
Insecticides - an Ounce of Prevention?
What about insecticides? At present, two chemicals effective against all southern pine bark beetles are available, but this could change with new Environmental Protection Agency rulings. See your county agent about approved insecticides, amounts to use, and methods of application. Of course, be sure to read instructions carefully and to handle such compounds cautiously.
How to Control Beetle Spread
But what if it is already too late for an ounce of prevention? By the time you spot the telltale symptoms of beetle attack - pitch tubes, feeding cuts in the inner bark, and fading of tree foliage - it is too late to save the tree. You have only one move left. Stop beetle spread.
You can do this in two ways. First, if the beetles are still under the bark of the dead or dying pine, cut it down and haul it away or burn it. This should break up the center of beetle emergence and stop them from infesting other trees.
Second, spray the attacked pine with an approved insecticide, which will kill eggs, larvae, pupae, and adults still under the bark. Or, you can spray uninfested trees adjacent to the one under attack to protect them during the period of beetle emergence. Whichever method of control you choose, you must act quickly or the beetles will spread to other pines.
A Check List for Coping with Beetles
The authors thank the Boyce Thompson Institute of Plant Research, Inc., for permission to use the chart on southern pine bark beetles, drawn by Richard Klieforth. For photographs, we thank the Georgia Forestry Commission in Macon, Forest Insect & Disease Management in Atlanta, Ga., and Asheville, N.C., and State & Private Forestry and the Bark Beetle Research Work Unit in Alexandria, La. We also appreciate the manuscript reviews and other assistance given by Extension-Forest Resources of North Carolina State University, the Texas Agriculture Extension Service of the Texas A&M University, the Texas Forest Service, and State & Private Forestry in Alexandria, La.
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Last updated on Wednesday, August 09, 2006 at 01:11 PM
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