The Juniper twig girdler, Periploca nigra, is a small moth whose larvae can significantly damage a bonsai. The adult moth appears in late spring to lay its eggs among Juniper branches, typically at branch junctions. The larvae burrow into the branch and begins to eat away at the cambium.
While a general pesticide can be used to control the adult moths it is difficult to time the spray when the moths are present because they are nocturnal. The larvae are protected under the bark and must be found and removed manually. It is critical to regularly scout for these hidden insects through out the year. As spring approaches, the larvae are bigger and easier to find but could have already done significant damage. Once they pupate you have lost your chance to stop the cycle because the moths will return to the same plant to lay their eggs.
When scouting for the larvae have some type of magnifying lens and a metal picking tool. You are looking for signs of insect activity like frass, and a bulge in the branch from a wound that is trying to heal.
…with a face only a mother could love.
As you can see the Juniper twig girdler lives up to its name. In bonsai every branch is important, and a few twig girdlers can decimate a once beautiful bonsai. Now that you know what these tiny tree terrorists look like you’ll be able to protect your junipers for years to come.