Question of the Week Number 1: July 12, 2018
“Why is my tree dropping so many small branches? They all look like they’ve been cut off.”
You’re seeing the work of a large beetle, the twig girdler. She’s a crafty soul, and there’s not much you can do to stop her. Let me explain.
Adult twig girdler beetle has patiently scored the small branch with her mouthparts after laying her eggs out toward its tip.
The adult female twig girdler finds small branches of pecans, elms, and other large trees. She deposits her eggs within the wood of a branch. Then she moves back down on the branch and starts scoring the bark with her sharp mouthparts.
Around and around the little branch she goes until she has cut almost completely through it. In the process, she has cut off all the flow of water and nutrients into the twig, so the tip of that twig dies, dries and eventually drops to the ground.
Base portion of elm tree remains intact after twig girdler severs the top.
Top portion of branch has fallen and dried. Young larvae are beginning to develop inside it.
As the twig rests on the ground the eggs hatch and the twig girdler larvae begin to feed on the wood of the small branch. Eventually they mature and are ready to emerge as adult beetles so they can mate and begin the cycle all over again.
So where is your remedy? You can’t really spray for the mother twig girdler because she’s only there for a few minutes. You can’t get a spray into the twigs to control the larvae because they’re protected by the plant’s tissue. Since the twigs are severed, systemic insecticides won’t help.
So you really don’t have a lot of good options except to rake up the twigs and either burn them or send them off with the trash. Neither of those choices is perfect, but each of them will help.