by Bill Eck
ISA Certified Arborist MA-4657A
After a 17-year rest, a large number of cicadas will be emerging in May of this year and could cause significant damage to your trees and shrubs. This is not a recurrence of the major emergence of Brood X that was seen in this area in 2004, but a slightly smaller event, Brood II. The map shows the areas of highest predicted concentration of Brood II based on the distribution of their parents in 1996. Cicada populations may exceed 1.5 million per acre in some areas.
More than 80 species of trees and shrubs are commonly used when the cicadas lay their eggs. Oak, apple, hickory, maple dogwood and members of the rose family are among the preferred species. The twigs of trees and shrubs can be severely damaged through the egg-laying of the female cicadas which insert a saw-like tubular organ into the bark and wood of twigs and cut a pocket into which eggs are deposited. One female may produce as many as thirty-five bark punctures. Repeated attacks can girdle twigs and may kill small trees and shrubs. The wounds also provide an entrance for disease causing organisms.
Adult cicadas begin to appear once the soil temperature is consistently 64 to 65 degrees for several days. Our soil temperatures in this area were hovering around 55 degrees as of April 21st. Adults live for only a few weeks, during which time they mate and lay eggs in twigs of trees and shrubs.
Spraying trees to prevent adult cicada damage has rarely been successful. There is no known method of controlling the nymphs in the soil. In areas where peak adult emergence is expected, the branches of small trees and high value shrubs can be protected with netting. Drape the netting over the entire tree canopy, and secure it to the trunk so no cicadas can crawl under the opening. Disposable mesh bags and plastic 1/4” netting are now readily available for this purpose. Netting is available at both Johnson’s and American Plant or you could purchase netting online here.
If your shrubs and small trees are too large and/or too numerous for you to cover by yourself, then you should contact your arborist or landscaper for help protecting important plants. Female cicadas will not begin laying eggs until at least one week after they first emerge, so protection needs to be in place by that time.
Fertilization will increase plant vigor and help offset the debilitating effects from the twig and branch dieback. Damaged plants should be inspected by an arborist to determine if borers or fungal diseases need to be treated.