Landscape - Twig Drop in Oak

If you are called by a client to investigate twig drop in oaks this time of year, there are two common causes. The following is an article on the subject from Rutgers University.

Observations during the fall season may show numerous fallen twig branches on the ground beneath a client’s favorite large oak tree. Usually the twigs are not much more than ¼ inches in diameter and the leaves are still attached. Two possible causes for the fallen twigs are from activity by gray squirrels or by an infestation of twig pruners (roundheaded beetle borers). Gray squirrels are notorious in the fall season for “attacking” oaks and other large trees during the weeks prior to leaf drop. They litter the ground beneath trees with twigs less than ¼ inch in diameter after chewing them off and letting them drop to the ground. When examining the end of the twig, look for the characteristic bevel or slant cut chewed by the squirrel. A couple of possible reasons for this squirrel behavior are to get acorns to the ground and to use the twigs and leaves for nesting materials.

Twig pruners are native longhorned beetles and are often found feeding on open grown oaks and other deciduous shade trees. The larval stages that feed within the twigs and small stems are called roundheaded borers. The larvae of this single generation borer will feed and grow in the twigs during the summer months. However, by late summer most of their feeding damage has been sufficient to girdle and weaken the twigs. Winds that are strong enough can then cause twigs to snap and fall to the ground with the larvae still inside. If an accumulation of fallen twigs becomes apparent in August and into September, then they should be examined for the possible presence of this borer. The broken ends will have a concave cut and the white larvae can be observed by cutting lengthwise at twig ends. The twig pruner overwinters as pupae within the fallen twigs/stems and emerges as longhorned beetle adults the following year in May/June. This minor pest can successfully be controlled with sanitation cleanup during the fall months. The use of insecticide sprays is not needed or recommended.

Reprinted from "Landscape IPM Pest Notes" by Steven K. Rettke, Ornamental IPM Program Associate in the October 7, 2007 Edition of the Plant and Pest Adivsory, Landscape, Nursery and Turf Edition from Rutgers University.