Bark beetles and similar groups of wood-boring beetle species target trees under stress or which were injured, either by storm damage or fresh pruning cuts (if pruning was extensive). Our Conifer Bark Beetles on Trees and Shrubs web page, linked above, provides more detail. Prevention centers around minimizing tree stress, such as by watering when needed during drought. We can consult with one of our Extension entomologists with bark beetle and ambrosia beetle experience about any specific questions you may have about wood-boring beetle damage, though he works with commercial entities (landscapers, arborists, nurseries) and makes recommendations for pest prevention plans in those settings that won't always apply to residential environments. Have you been able to have a certified arborist assess the pines remaining to determine if there are any sources of tree stress that can be remedied (girdling roots, etc.)?

Miri

Dear Miri,

Thank you for answering my email concerning bark beetles!  I found your email, and it's links to other information, very informative- especially the UMD Extension article "Conifer Bark Beetles on Trees and Shrubs".  I've been doing some on-line research about the beetles, but didn't find anything that was as complete as the one you provided.  I see it was even recently updated on February 28, 2023. 

In answer to your question about having a certified arborist assessing the trees, I have been in communication with the certified arborist who works for the tree company that removed the dead loblolly.  He noted that there isn't much that can be done to save a tree once it's infected and has suggested two different methods of trying to keep healthy trees from becoming infected:  1) spraying the bark of the trunk approximately 10 to 12 feet up from the base with an insecticide and 2) injecting an insecticide to the base of the tree in the soil and roots.  Both of these methods sound OK to me for beetles that attack the lower portion of the tree, however they're expensive.   As far as minimizing stress to the trees, it isn't practical for me to water them since they are very large pines and not very close the water supply from my home.

You mentioned that you could consult with one of your Extension entomologists about specific questions.  This would be very helpful to me and I was wondering if you could ask if there is a way to determine if a tree is infected other than just looking at the limbs and bark?  For example, can core samples be made by drilling into the inner bark layer without threating the life of the tree?  This could be done by selecting say, a one-foot square area that has what looks like entry and exit beetle holes and then using a core type drill to produce several plugs that could be examined for beetle galleries, larva dust, blue stain from fungi, etc.  Something tangible like this core-sample test, plus looking a the tree limbs and crown would be helpful in convincing me to spend the money to try to save the healthy trees and also to remove those that are infested.  If there are other tests that are used I'd be interested in knowing about them too.

Sincerely,

Martin 

  

Hello Martin,

Thank you for the additional information. The arborist is correct -- once borers are inside a tree, little (if anything) can be done. Some beetles merely chew tunnels ("galleries") in the wood (and which type of wood they use makes them more or less damaging), but some deliberately introduce a fungus to their galleries and feed upon its growth, so it's a dual situation of fungal and insect damage in that case, neither of which can be treated.

Insecticide sprayed on the bark is meant to kill adult borers (usually a type of beetle) that land on the tree to lay eggs, or which emerge from the tree to begin another generation, since they aren't laying eggs within the galleries. These kinds of insecticides tend to be in the chemical class called pyrethroids; as synthetic versions of the naturally-derived pesticide pyrethrin, they are meant to last longer to be more effective before they degrade. The residues insects come into contact with (they don't have to be present and contacted directly by the spray, as with some less-toxic pesticides) after a treatment are non-selective, meaning they can potentially kill any insect that encounters them, beneficial or otherwise.

A trunk injection probably also uses a non-selective pesticide (to be fair, hardy any are selective for borers like beetle or moth larvae), and it might be somewhat systemic, which means it's moved through the tree's tissues from the injection site to other areas. (Maybe the canopy, maybe not...depends on the dose and chemical involved. The arborist could speak to this.) For flowering plants, this may risk pollinator exposure, but in the case of pines, is probably limited in its impacts, though we don't know if it would wind-up in canopy foliage or pine cone seeds that other wildlife uses (birds, harmless caterpillars, etc.).

Nothing can reverse any existing borer damage; at best, an insecticide would interrupt life cycles to prevent future insect generations from colonizing the tree, but the tree can't repair any galleries or accompanying fungal infection already present. Therefore, whether such expensive treatments are worth trying may depend on how light or heavy existing damage may be.

Core sampling the wood will not diagnose a borer infestation, and fungal growth (like the "ambrosia" for ambrosia beetles) tends to stay close to the gallery it was introduced to. The sawdust generated by drilling-out a core sample would obscure any sawdust produced by a borer. Borers can't really be identified or confirmed until outward symptoms of their presence are manifesting -- sawdust, oozing sap, and/or emergence holes. (Accompanying the death of wood under the bark can also be areas of detaching bark.) The emergence hole characteristics (its diameter and shape) can help narrow-down which borer species might be present, but often the insect itself needs to be captured to concretely ID it; for example, some ambrosia beetles require microscopic examination to tell them apart. There may be pheromone traps that can be put out for detecting when certain borer species are out and flying (looking for mates, so males get drawn into the trap), but not for all. Additionally, there are alcohol-baited traps of scrap wood that are used to detect ambrosia beetle activity (since dying trees tend to produce alcohol in small amounts the beetles can smell), but here too, it just tells someone when to apply a preventative trunk spray, not that a given tree is already infested.

While tree decline and canopy dieback may tip-off a gardener or arborist that borers might be responsible in lieu of sawdust or sap ooze being observed, it's a late-stage symptom to rely on, and can occur with a wide variety of other circumstances causing tree decline. Plus, borers could very well overlap with other issues contributing to decline, especially since they are rarely the first and only issue damaging or stressing a tree. Unfortunately, there is no easy solution to this issue, and minimizing tree stress (when possible) is the best approach to preventing the borers without relying on yearly pesticide applications. We acknowledge the unfortunate reality that there is only so much that can be done when trees are stressed by weather or soil conditions, and you may have to decide between the one-time cost (per tree, anyway) of eventual tree removal if they succumb to borers or other problems, versus the yearly preventative insecticide treatments to discourage future borer outbreaks (keeping in mind that a different issue might still arise that necessitates tree removal later).

Miri

Hi Miri,

Your detailed response to my question shows I've found the expert I was hoping to hear from.  

The solution to this bark beetle problem is important to me because I'd like to save the large (>100 feet tall) loblolly trees in front of my house.  There are nine of these beautiful trees.  All of them appear healthy, but they do have evidence of beetle holes.   Only one tree seems to have a slightly lighter-green crown (It's neighboring tree was the tree that died-and was removed).   As you indicate, it's difficult to know for certain whether or not a pine is already infected. Once you observe the yellow needles and dead limbs in the crown it's too late.

Unfortunately, it's a gamble between hoping a loblolly pine can withstand bark beetles on its own versus spending money for insecticides that may or may not solve the problem.  The cost of removing one of these pines is about $1,500 (without stump grinding).  Whereas, the cost of treating all nine trees with a spray insecticide is about $600 (for 2 sprays/year) and about $900 for a systemic insecticide soil drench application that's done once per year.  In addition, there's a concern these insecticides could be dangerous to humans, good insects, birds and other animals,  

As you noted in your last paragraph, I'll need to "decide between the one-time cost per tree of eventual tree removal if they succumb to borers or other problems versus the yearly preventive insecticide treatments to discourage future borer outbreaks". The worst case would be all nine trees needing to be removed in one year:  9 x $1,500 = $13,500.  If only one were to die per year it would be $1,500 per year vs $600 to $900 for an insecticide treatment.  If a tree were to die every other year, that would average out to be  $1,500/2 = $750 per year which is about the same as the cost of an insecticide treatment each year.  

Since all nine trees currently seem healthy and insecticides are possibly dangerous, I've decided to do nothing for now.  I'll keep watching the one tree who's crown currently looks suspicious and then reassess the problem.  If it's crown begins to  have yellow needles and dead limbs, I'll consider doing a bark-core-sample-test using a 2 to 3 inch diameter bit like the one used to drill a hole to insert a door knob in a wooden door.  These bits have cutting teeth around the circumference and hollow centers which produce a plug of wood that can be removed from the bit and examined.  This will give me one or more plug samples large enough to see is there's beetle activity in the layer just below the bark.  I'm thinking these plugs won't be life threatening to a healthy tree.  Much larger sections of bark are removed from loblolly pines for turpentine production without killing the tree.

Thank you again Miri.  Your help and expertise is very much appreciated!

Martin 

You're welcome.