In a few weeks the adult phase of the Brood X periodical cicadas will be gone. For most people it appears to have been an interesting experience. It bridged some slow news times and provided the subject for some interesting banter to offset blathering about the hockey fights on the evening news.
But there are yet some things to attend to if we're to put these insects to bed for 17 years and still avert an overreaction to the "damage" they will leave. The eggs have largely been laid, stuck under the bark of twigs, and some of the twigs are beginning to die. On large trees, the leaves within eight to 10 inches of many branches will turn brown and the tip will die. In most cases the tip will break and hang down or "flag." This will not be harmful to those large trees which, in fact, will be more damaged by squirrels. Some even say it is a beneficial pruning. At worst, it will not offset the benefits of the gas interchange and water percolation provided by the tunneling cicada nymphs before they emerge.
Damage to the tips of unprotected smaller trees is, however, more serious. The growing top branches of my 7- to 10-foot dogwoods are laced with egg scars and I can see that part of the tree will die. Next year, a side branch will take its place, but the trees will be set back some.
The thing to remember is that this could only have been prevented had I put a net over the trees. Pesticides wouldn't have helped. The females still could have laid their eggs before they died, and pesticides would have killed the numerous ladybeetle larvae wandering about looking for aphids. So, the unprotected dogwoods and other ornamental trees are going to be on their own. I'm sure they will be able to handle it; there are many worse things that can and probably will happen to them.
Now it's time to buck up and help these young trees get through the cicada stress; they will be better off during the next emergence of Brood X in 17 more years, and will hardly remember the summer of '87.
Extension Entomologist, University of Maryland