Death by Borer

It happened this week, and I’m having a rough time of knowing that I’m going to have to say goodbye to one of my favorite trees.

While pruning the snow damage off of our ‘Twisty Baby’ Locust (Robinia pseudoacacia ‘Lacy Lady’), I noticed that a few odd-looking notches and shadows in the branches of the tree. My heart sank and I hoped that I wasn’t looking at borer damage.

Locust Borer Damage

Unfortunately for the tree, I was. The nasty Locust Borer (Megacyllene robiniae), has been dining on it for what appears to be several seasons. This pest is one of the reasons why the general species of Black Locusts, one a promising tree for land reclamation and the lumber industry, is no longer recommended for large scale planting.

Signs of Borer Activity

  • Holes where the larvae has bored into the tree
  • Sap Leakage at the bore site
  • Frass – a sawdust looking material left by the insect larvae
  • With severe infestations ‘sawdust’ can often be seen at the base of the tree
  • Branches, limbs, and leaves that appear to be slowly dying or are dead,  with mature trees, often the upper portion of the canopy is dead or dying
  • Cracked bark, often with swelling or a spongy feel to it.
  • Frequent visits to the tree by woodpeckers or other insect seeking birds
  • In spring or late summer you may see moths or beetles along the trunk or branches of the plant as they seek locations in the bark to lay their eggs

There are sprays that can be used to treat borers, but the success rate is very low, given that the tree that is its food, is also providing a protective shelter.

Locust Borer damage

Sap spots, as shown in the image above often indicate the borer’s entry point into the plant.

The fate of this unique and beautiful tree is to be removed and burned, ensuring that the larval form of this pest cannot complete its lifecycle and go on to damage or kill other trees.

Hidden Borer Damage

A few elements of hidden borer damage can be seen in the image above – frass (bug poo), shadows and a ‘spongy’ bark.

I have borers, what can I do?

  • If the infestation is isolated to a branch or two that is within reach, you can carefully prune out the infected wood and dispose of properly.
  • With limited infestation, careful pruning, watering, removal of plants the adult form of the borer needs to complete their life cycle, and appropriately timed insecticide application can be effective in preventing further issues.
  • If the infestation is severe, removal is the best option. Attempting to treat with an insecticide is rarely successful as the larval stage (the boring stage) is protected by the bark, sapwood or even heartwood of the plant.
  • Contact a local arborist who can inspect your tree and provide you with the best options for your situation.

*Phew* I Don’t have borers, how can I keep it that way?

  • Trees that are less than 6″ in diameter, have been recently transplanted, or have marginal hardiness for your location  are most susceptible to attack.
  • Know your plants – know what their pests are, and when they are most active; know how to treat your plant for them.
  • Regularly inspect your trees and shrubs for pests and signs of damage.
  • If you don’t need to use tree wrapping on your saplings, don’t. While they may protect against sun scald in some species like maple, the use of wraps can slow or prevent the toughening of bark – which is the plant’s first line of defense.
  • If your tree or shrub seems to be having a hard time breaking out of winter’s sleep, inspect it carefully, that’s usually the first sign that you have bugs.

There are borers that attack root systems, and those are more difficult to identify. If you have questions or need assistance in identifying what’s bugging you or your plants, CSU Master gardeners and local nurserymen are incredible resources and can help you problem solve your situation.

I am pained at the loss of this multi-seasonal specimen, but we will use the opportunity to sketch out ideas and begin looking for a tree or large shrub that meets the requirements of our yard, and pest resistance is higher on the list than it once was.

FFC 16-0415 Borer 03

Borer damage is easily visible once the ‘spongy’ bark is removed.

In a future post, I’ll share a checklist of questions that you can use when selecting trees or large shrubs for your home or project, including those about pest and disease resistance.

Until next time, may your knees be green, and your spirits light.



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