By Kevin Daugherty
Every summer, it seems I have this discussion with several landowners. Mortality of single or small groups of pine trees in timber stands, pastures, and even yards has been a common occurrence over the past few years. These trees had no apparent injury and seemed healthy until their needles started turning yellow and then red.
The culprit is most likely bark beetles, and specifically Ips engraver beetles. Engraver beetles are small, brown to black, insects that attack and kill pine trees by feeding and laying eggs in the inner bark of the tree. They usually exist harmlessly in fresh logging debris and weakened trees and don’t kill enough to be considered a major pest. However, when trees are weakened or stressed, a significant number of trees may be attacked.
Several things can weaken or stress pine timber. Drought, flooding, wind, careless logging, fire, disease, root damage from traffic, and other factors make pine trees susceptible to an engraver beetle attack. These days, it seems like every weather system spawns a few tornadoes that wreak havoc on the trunks, limbs, and root systems. Another very common stressor of pines is lightning. When I inspect a tree that has been infested, I often see a lightning scar. Tall pine trees are like lightning rods. Unless the strike passes completely through the trunk, chances are fairly good that the wound will close and the tree will survive. While the tree is recovering, however, it’s a prime target for bark beetles. Simply put, stressed trees don’t make sap as well as healthy trees and that sticky sap is the trees primary defense against these beetles.
The first and most obvious sign of attack by engraver beetles is the presence of “pitch tubes”, which are small yellowish-white masses of resin on the bark that mark the points of beetle attack. However, in weakened trees pitch tubes may not form and only boring dust will be visible. As mortality sets in, the needles become yellowish, then change to red, and within one to two months, become brown. The stress that made the tree susceptible, the insects tunneling in the cambium, and the blue stain fungus they introduce, is often too much for the tree to overcome.
There are actually three main species of bark beetles that attack pine trees: Ips engraver, black turpentine, and the
dreaded southern pine. Southern pine beetles (SPB) are the most destructive insect pest of pine in the southern United States. When a pine tree dies and evidence of insect activity is present, many fear they’re facing a southern pine beetle (SPB) outbreak. While engraver beetles usually infest solitary trees or a small group of trees, SPB can wipe out many acres. Its scientific name, Dendroctonus, actually means “tree killer”. Fortunately, we haven’t seen a widespread outbreak here in central Louisiana since the mid-1980s. It’s not a coincidence that this followed a severe storm system that caused widespread timber damage throughout the area. Fortunately, we haven’t seen much SPB activity in quite a while. Winn Parish, for example, hasn’t experienced even a small infestation in several years. There have been some large outbreaks in Mississippi recently, which gives us cause for concern. Fortunately, the Louisiana Department of Agriculture and Forestry monitors these insects with traps, and, though they catch a few SPB, the numbers haven’t been enough to cause alarm.
So how do you know which beetle is responsible for the demise of your tree? Aside from the fact that SPB is usually more widescale, sign left on individual trees often has several similarities. On the outer bark, the pitch tubes mentioned earlier and small holes that look like the tree was hit with birdshot may be present. The pitch tubes are where they bored in and the “shot” holes are where they exited. Ips and black turpentine holes will usually only be on the lower section of the trunk, up to eight or ten feet. SPB pitch tubes will go much higher up toward the treetop. If you peel a section of the bark off, you’ll see the galleries and chambers bored into the inner bark. The tell-tale sign of SPB is “S” shaped galleries. The galleries of engraver and black turpentine beetles will be “H” or “Y” shaped. As stated earlier, if it’s an individual tree or just a few trees, it’s probably engraver beetles.
The most practical approach to minimizing timber losses is to maintain forests in a vigorous, healthy condition. Good timber management practices lessen a stand’s susceptibility to all pine beetles. Timely thinning of the stand can be a preventative measure that will help reduce future beetle damage. Unfortunately, there really isn’t a practical direct control option and certainly not one to save an infested tree. Cutting and removal, where practical, is about the only course of action.
Kevin Daugherty is a forestry and wildlife consultant, real estate agent, and the managing member of ForestLand Associates, LLC. He’s a member of the Association of Consulting Foresters, Louisiana Forestry Association, Society of American Foresters, and is a Land Certification Inspector for the Quality Deer Management Association. He and his wife live in rural Winn Parish. For questions about this article Kevin can be reached at (318) 312-1240 or firstname.lastname@example.org