Borers

Borers.  It’s a common term you hear when discussing tree issues.  It’s also incredibly broad.  The term borer describes the method in which the tree is impacted by the insect’s larval stage rather than the adult- and the groups of insects being described by this one term are incredibly diverse!  The two most economically impactful groups of borers are Flathead Borers (Buprestidae)-

Bronze Birch Borer, A Flatheaded Borer

Bronze Birch Borer, A Flatheaded Borer

Emerald Ash Borer, Bronze Birch Borer (Right), and Two Lined Chestnut Borer, just to name a few- and Roundheaded Borers (Cerambydicae)- Asian Long Horned Beetle

Ash Lilac Borer, A Clearwing Borer

Ash Lilac Borer, A Clearwing Borer

and Pine Sawyers are good examples of this type.  But there are others.  Oh yes, there are others.  Clearwing Borers (Sesiidae,) such as the Ash Lilac Borer (left) aren’t even beetles, they’re members of the order Lepidoptera (Butterflies and Moths), in this case, Moths.  Are you ready for the fun part?  Clearwing borers aren’t affected by the same active ingredient generally used to take care of lepidopterans, or Flat- and Roundheaded borers because Clearwing Borers tend to hang out in the parts of plants that systemic treatments don’t reach!  Aren’t borers great?  Wait, there’s more!  We’re back in the beetle family with Weevils (Curculionidae), such as the Wood Boring Weevil, and Bark Beetles (Scolytidae), like the Mountain Pine Bark Beetle, which also contain species that bore through the vascular tissues of trees as larvae.  So, we’re essentially looking at five separate taxonomic families (quick review: living things are classified at seven levels- Broadest to narrowest: Kingdom, Phylum, Class, Order, Family, Genus, and Species.  Example for Emerald Ash Borer (Agrilus planipennis): Kingdom Animalia (animals), Phylum Arthropoda (arthropods), Class Insecta (insects), Order Coleoptera (Beetles), Family Buprestidae (Metallic Wood Boring Beetles), Genus Agrilus (Jewel Beetles), Species planipennis (Emerald Ash Borer).  We tend to work in the family range of taxonomy in Plant Healthcare when dealing with insects).  Just for an idea of how large these families are, these five families contain roughly 82,000 species of insects spread across the world.  Not all of those are economically important as pests of trees- but the ones that are, are incredibly important.  For the purposes of this article, we’re going to focus on those most impactful on shade trees of the urban landscape, which puts us squarely on the Flatheaded and Round Headed boring insects, our friends in Buprestidae and Cerambydicae (we use the term “friend” pretty loosely at the Tree Geek).

Flat Headed Borers have been getting the most press lately.  We have many native species of Flatheaded Borers that are significant pests, such as the Bronze Birch Borer- which can have major impact on nonnative birch species- and the Two Lined Chestnut Borer- which is a major pest of Red and White Oak species.   The big concern in many states right now, however, is the Emerald Ash Borer.  This is decidedly not native.  It came from China, and is found around the same latitude as Minnesota (sidebar- this is likely bad news for the folks hoping our cold winter killed off a significant portion of the population in the northern states).  They key

Flatheaded Borer Larvae

Flatheaded Borer Larvae

Roundheaded Borer Larvae

Roundheaded Borer Larvae

distinguishing factor for these borers is right there in the name.  Their larvae have a shovel shaped, very flat head (above left), in contrast to the round shape of a Roundheaded Borer (above right).  The adults look very different as well.  Adult Flatheaded Borers tend to be smaller (Emerald Ash Borer could line up three bugs side by side on a penny), and have a metallic sheen to them.  Round Headed Borers are usually a bit larger and look more like a traditional beetle.  They are often called the Longhorned Beetles because of their long antennae, shown here on the Asian Longhorned Beetle (below right).  The other key factor in determining which type of borer is attacking a tree is the type of exit holes you see

Asian Longhorned Beelte, A Roundheaded Borer Adult

Asian Longhorned Beelte, A Roundheaded Borer Adult

on the bark of the tree.  Because of their

Flatheaded Borer Exit Hole

Flatheaded Borer Exit Hole

flat head shape, Flatheaded Borers will leave a distinctive “D” shaped exit hole when the adults emerge from the tree (below left).  Roundheaded Borers will leave a round exit hole as the adults emerge.  So, there you have it: Borers.  There are a ton of them, and they can be major tree pests.  Many of them, though, are relatively easy to treat yourself, and The Tree Geek has plenty of options to help you out.  For more information on specific pests, check out our pages dealing with Emerald Ash Borer, and Bronze Birch Borer, or give us a call!  We’re more than happy to walk you through your tree issue and explain the how and why of what you can do about it!

4 Responses to Borers

  1. Dianne says:

    Hi, I believe I have a bad case of Bronze Birch borers on a weeping birch. I overpruned this tree last fall and we had a brutal winter so the tree was stressed. I just noticed the holes this week. I first thought the failure was from overpruning I removed the dead branches a month ago and more began to die. I decided to leave it alone and see what would happen and just discovered the holes. The tree is 50% compromised, I have another one in close proximity that is fine. So, do I remove or treat it. Its about 5-7 yes old. Thanks for your suggestion’s in advance!

    • The Tree Geek says:

      Hi Diane. Sorry to hear about your Birch. At this point, I would probably remove the compromised tree, it’s pretty far gone. I would also consider treating the other tree. Bronze Birch Borer typically only attacks trees that are already stressed out, so make sure your other tree is getting plenty of water- Birches love water! I say BBB typically attacks stressed trees, because even a healthy tree in close proximity to an infested one can be a tempting target, so watch that one for symptoms. You’ll first notice a thinning in the top of the crown with top down die back, and possibly swelling under the bark where the larvae have been tunneling. BBB can take down a tree pretty fast, so if you want to treat that one preventatively, you could consider Xytect or Optrol either this fall or next spring.

  2. Mike Burge says:

    Hi there, I have many Swedish Aspen and have noticed a lot of holes in them with a lot of sap running from them. On top of that a lot of frass at the base of the tree. I suspect I have a borrow some sort but not sure what kind or how to treat them because I can’t get at them. I am wondering if there is any kind of systemic I can use to get rid of them before they eradicate all my trees.

    • The Tree Geek says:

      Hi Mike,

      The key to adequate treatment is proper identification. It does sound like you have a borer problem, but treatment can vary based on the kind of borer. Flat-headed borers can be treated effectively with systemic insecticides since they spend the majority of their life boring through the sapwood. Other borers such as: bark beetles, ambrosia beetles, and poplar borer have been unsuccessfully treated with systemics. Generally, most university extensions recommend a permethrin based insecticide used as a trunk and limb spray. Based on the description I would look into the spray option, but without seeing the tree it is tough to say. I would get confirmation from a university extension agency near you, or have an arborist look at it before moving forward with any treatments.

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