Pine Bark Beetles

There is a feeling that can only be described as a “violation.” You may know the feeling; you walk to your barn and find out someone has violated your space, stolen tools or equipment. First, there is shock, then anger. There is a similar feeling when you find your pine trees have been attacked and killed by pine bark beetles. There is shock and anger followed by what I could have done to prevent this and what can I do to prevent them from spreading to the rest of my forest.

“The Southern Pine Beetle (SPB)- (Dendroctonus frontalis) is the most destructive insect pest of pine forests in 13 Southeastern States and in parts of Mexico and Central America,” said Thomas L. Payne of Texas A&M. “This is a well-worn statement but nonetheless richly deserved and quite accurate. The beetle ideally represents the definition of its genus – killer of trees.”

The life cycle of an SPB is not so different from that of thousands of other insects. Eggs hatch and become larva inside the bark of a host tree. By the time a property owner sees the tree dying the adults have emerged through tiny holes and either flown or been carried on the wind to a new host tree.

According to a study at the University of Kentucky, beetles generally leave the host tree and aggregate on a nearby tree; however, some may travel several miles, carried by strong winds, before attacking a new tree.

When adults successfully attack a new host tree, they produce a pheromone or chemical scent that attracts other males and females. Within days, thousands of beetles may attack a tree and overwhelm its defenses. Excess beetles land on, and colonize nearby trees, creating “hot spots,” and the infestation expands.

Southern pine beetles are considered cyclic and outbreaks may seem more severe some years than others. Couple those outbreaks with extended droughts, overcrowded stands, aged trees, and the threat multiples.

A healthy, well-managed timber stand is the best defense against these tiny tree thieves. Landowners should follow those best management practices set forth by schools of forestry, the U.S Forest Service, and State Forestry Associations. Many best forest management practices may be found within the pages of this magazine. Previous articles include using herbicides to remove undesirable undergrowth such as privet or sweetgum, and the use of prescribed burning.

From the time an egg is laid in a host tree until an adult emerges is roughly 26-54 days. In Virginia and North Carolina, the northern edges of the SPB known range allow for as many as three generations per year. In the south, from Texas to Florida and into Mexico it may be as many as nine generations annually. Newly infected trees, indicating the direction of the progression, will have yellowed needles in the tops of the trees, contrasted by the dark green of a healthier neighbor. The yellow will give way to brown (red) as the tree succumbs to the infestation. In most cases, these trees are still marketable and should be cut or removed from the property as soon as possible.

Know Your Pine Bark Beetles

At this point, it is sufficient to say volumes have been written about the pesky little beetles that are the bane of the nation’s pine plantations. We humans have to take some blame for the whole sordid event. From our bare earth approach to logging and farming to our reforestation efforts that focused on pine plantations as far as the eye could see. This included the indiscriminate killing of hardwoods which acted as natural beetle buffers. But there is no need to point fingers. Timber Stand Improvement or TSI is a fluid activity and needs adjustment from time-to-time

For the gamekeeper, there is some timber management that will aid in preventing the spread of a beetle outbreak. Unless you are advanced in timber management skills or have enough free time to devote to educating yourself, consider hiring the services of a Certified Forest Manager. Such an investment will place boots on your ground with the knowledge of your soil and forest conditions. Such a manager will come up with a long-range plan that might include limited or select harvest, understory control, water management, controlled burning, and species replacement.

Three groups of southern pine bark beetles in the southeast are wreaking havoc on pine forests; each has its own distinguishable features and characteristics. The three groups of southern pine beetles are the southern pine beetle (SPB), the ips engraver beetle (IEB), and the black turpentine beetle (BTB). Each beetle will initiate an attack based on specific causes and each will basically attack a different area of the tree. Some attack at the stump, while others attack as high as 30-40 feet or in the crown. This is one reason the application of an insecticide is not considered economically feasible.

All species of pine are susceptible to infestation, but the bugs prefer loblolly, shortleaf, Virginia, pond, and pitch. Longleaf and slash can be infected but seem to offer some resistance not found in the aforementioned.

Beetles leave distinctive patterns in the cambium layer of the infected tree.

According to university studies, southern pine bark beetles generally attack less vigorous or stressed pines, especially ones weakened by a continual drought, such as those dry spells in 2015 and 2016. Storms, including hurricanes, severe thunderstorms, and tornadoes may weaken trees. Severe fires, overcrowding, and prevailing diseases also weaken a tree’s defenses against pine beetles.

According to Marc Measells, an Extension Associate III in the School of Forestry at Mississippi State University, the right thing to do may also be something less than pleasant.

“Pine plantations planted on the current 10 x 10 spacing will become too crowded too soon and need thinning,” Measles said. “Thinnings,” as the long narrow logs are sometimes called, are good for nothing more than pulpwood and may garner around $1 per ton.

But at this point in your forest’s production life, it is better to sell what you can for the health of the remainder. Think of it as a sacrifice for the greater good. A subsequent sale will result in chip and saw quality logs and bring more money. At the end of a 40-year rotation remove the saw logs when they are at the desired size and replant.”

Here you see a “hazard map” of the southern pine beetles’ range

Second, only to the Southern Pine Beetle is the IPS. An IPS beetle attack is usually confined to the crown (although capable of attacking the whole tree) and is characterized by needles turning yellow or red. Dry, reddish-brown boring dust will be present in the bark crevices as well as white to brown pitch tubes along the trunk. A successful attack can be verified by the presence of a small hole at the center of a pitch tube. This is where an adult beetle has entered the inner bark. If a hole is not present in the pitch tube, the beetle attack was unsuccessful.

Similar to the southern pine beetle, the Ips beetle carries blue stain fungus spores which stop the upward movement of water to the tree crown and causes the needles to wilt and die. The exit holes of the Ips beetles look like scattered shot holes on the outer bark. The IPS is common north to Minnesota and west to Colorado and beyond. The IPS and SPB range overlap.

Specific beetles have specific tunnel patterns, some in the shape of an S and others making a pronounced J. Others are far more random and leave no discernible pattern – just dead pine trees.

Bugging Out

When it comes to controlling pine beetles, terminology may be a little confusing. One term is “get in front of the bugs,” where “bugs” is the universal reference for the Southern Pine beetles or SPB. You may see all these terms scattered about in this and other articles.

Southern Pine beetles are weak fliers, so a reasonable buffer around an infestation will help prevent further spreading of the colony.

The U.S. Forest Service has a proven approach to dealing with infestations. They cut the trees into a circle, stumps to the outside, and tree-tops toward the center They cut the live or dying boundary trees at a site in the direction the beetles are going.

This is known as “getting out in front of them.” Dead trees, where the SPB will not attack behind the direction of aggression, may be left standing. There is no benefit to be gained by cutting dead trees compared to the man-power and expense involved.

Where an infestation has been cut into itself, such as what the USFS does, seed dispersal will generate a new forest within a short time. The mature seed trees will be native to the area and the genetic stamp will be such that the soil type, tree variety, and soil moisture should produce a healthy tree. In the meantime, briars, grasses, and early successional growth will be a great benefit to ground-nesting birds and other animals. The piles of rotten logs will produce an abundance of wood grubs and black bears will have a feast, so while some timber income will be lost, wildlife will benefit to a small degree.

Knowing the Score

The University of Alabama has a formula whereby a landowner/manager can assign a numerical value for SPB hazard. The time to compute the hazard score is before there is an infestation. The formula is a little intimidating to the mathematically challenged and is another good reason to enlist the assistance of forestry professionals. A professional is not a timber buyer or logger, who will have a tendency to encourage harvesting. The score is based on the pine basal area, total basal area, and stand age and site index.

The information is taken at each plot, with plots generally five chains apart (each plot represents approximately 2.5 acres). The data is then put into the formula to determine the score associated with the hazard class. The following formula determines the SPB hazard for a stand.

Score = 1.8342(Pine BA) + 0.4085(total BA) +. 0.705 (age) + 0.88(site Index) -206.315.

A hazard index of 220 or above is very high; 168 to 219 is high; 62 to 167 is Medium; 11 to 61 is low; 10-0 is very low.

Example:
If a total basal area is 130 sq, ft/acre, pine basal area is 120 sq. ft/acre, stand age is 27 years, and site index is 109.

Score = (1.8342 x 120) + (0.4085 x 130) + (0.705 X 27) + (.88 X 109) – 206.315 = 181.85

The score of 181.85 is between 168 and 219 means the relative hazard rating is “high.”

To reduce SPB losses in pine stands rated as a medium or high hazard, a registered forester might recommend:

• Thinning to basal areas of 70-100 sq. ft. /acre to promote rapid tree growth and resistance to beetles.
• On sandy soils, using borax on tree stumps to prevent annosus root rot.
• Harvest and regenerate over mature stands.
• Conduct prescribed burns to reduce competition.
• Treat hardwood competition with herbicide to reduce competition.
• When practical, remove high hazard trees preferred by beetles, e.g., those damaged by lighting, ice, logging, or other pests.

Sum it Up

The threat of pine beetle infestation is very real, but it is not a death sentence for the land. It does require some effort on a gamekeeper’s part. Especially important is to have a current assessment of your property. This is the time of year when most of us are on our property preparing for the upcoming hunting season. Be observant – look for stressed pines, make plans to remove them, even if they are property boundary trees. Chances are your neighbor is as worried as you about the possibility of a beetle infestation. If your property is difficult to cover, purchase a drone and learn to use it. Make regular reconnaissance trips around your property boundaries and if you see an issue on the neighbor’s land, let them know. Tell them what you both have to lose if nothing is done to contain the problem. In the end, we are not the owners of the land, but rather the current stewards. Our children and grand-children will be the next caretakers. It is our responsibility to teach them to do right by the land.

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