The appearance of dead foliage clusters scattered throughout the canopy of oak trees is very noticeable right now. Some of these twig-and-foliage shoots, called “flags”, are breaking away, littering the ground below. This is symptomatic of the oak twig girdler, Oncideres cingulata. Oaks are the most common trees to be afflicted with the oak twig girdler, but other hardwood trees can be affected too.
What is the oak twig girdler (OTG)? This is a long-horned beetle, ¾ of inch long, with antennae that are as long as its body. The OTG typically emerges in mid-August, with adult females chewing a shallow V-shaped channel that completely encircles the twig, laying one egg in the bark beyond the channel. Hatched larvae bore into the wood to feed, then overwinter in this protected environment even when twigs break from trees. There is one generation of the OTG each year.
What can be done about the oak twig girdler? First, the presence of flags within the canopy and on the ground does little in the way of damage to otherwise healthy trees. Often the full extent of the flagging has reached its peak by the time it is apparent, so insecticides will not be helpful. Clean up of fallen twigs and removing them from the yard will decrease the number of OTG larvae from emerging as adults next year.
Note that most of our trees within the region are living in drought conditions right now. Watering trees, from the newly planted to the well-established, is of utmost importance. Placing the end of a garden hose, set to trickle, beneath the tree canopy ensures a deep soaking with little water loss due to run-off or evaporation.