The "Locust Borer" aka What's Killing My Tree!

Locust Borer damage

Early this spring I noticed holes in my Purple Robe Black Locust Tree. Horrible name for a tree! Anyway, I rammed wire in the holes trying to hook or kill whatever bug it was that was causing the damage, with no success.   

Purple Robe Black Locust Tree

Fast forward to early September,  I noticed what I thought were wasps running all over the tree.  At closer look and some research, I found these insects are actually locust borers, (Megacyllene robiniae).  I initially thought this was a Wasp Beetle, aka Wasp Mimic Beetle aka Clytus Arietis aka Wasp Mimicking Longhorn Beetle, but those tend to live in deadwood and this is a living tree. Also the markings are not an exact match to the Wasp Beetle.

Once I identified the pest, it answered every question I had.  I first thought the tree branches split because it was windy and then the bugs came in chewing holes.  Turns out its the other way around!  The locust borer larvae came in, tunneled holes under the bark and branches.  This weakened the tree, making it susceptible to wind damage and split branches.

Locust Borer

Another thing I noticed about my purple robe black locust tree is it had a rather large bulge at the top of the trunk where the branches begin to come out. That is a result of scaring due to the damage going on inside.  The tree is trying to heal and strengthen itself so its bulking up the weak spots. 

You will also notice the sawdust deposits near the holes it makes.  The color of the fresh dust indicates how far the locust borer penetrated the tree. The more yellow the dust, the closer to the center.

Finally I noticed that the leaves began to fall way to early in the season.  By that time, it will be no surprise. 

Signs of infestation in order:

• Small wet spots on branches or trunk. This is the larvae beginning to tunnel under the bark in early spring when the buds appear.
• Broken or split limbs
• Knotty swellings
• 1/4" to 1/2" Holes appearing on the trunk or branches. Usually accompanied with wood dust.
• Leaves yellowing & falling out of season.
• Wasp looking bugs appearing and running around the tree in early September. (afternoons in my case) I collected about 10 of them.

Why bother trying to save this tree at all?  Well, I like the Black Locust Tree because it is a fast grower. Its currently the largest tree in the new home development that I live in. It grew from 6ft to over 25ft in the five years I lived here. Its also a great shade tree that allows some sunlight to pass through instead of blocking all light. Also the flowers it has in the spring are awesome. A gorgeous violet purple color. 

So treatment should be easy, as long and the infestation didn't get too far.  For just under $20 at Home Depot I picked up some BAYER Advanced Tree & Shrub formula.  Its a crazy bright green color and super easy to apply.  To figure how much to use you measure circumference of the main part of the trunk. In my case it was 15".  And thats how many ounces you put into the watering can (one gallon of water.)  The product comes with a measuring cup so its really easy. Then you just pour the green solution near the base of the tree.  It soaks up the chemicals in the roots and spreads it throughout the tree, killing all the beetles and other bugs inside. I am also going to put a little in a sprayer and spray the trunk and branches because it will also soak in and kill the pests.  One application should be effective for a year.  I can get two treatments out of a bottle this size.  

This is not a recommendation  for this product yet.  I will know how well it worked next year if I see any new holes.