Cicadas' Effects on Trees

For Trees, Cicada “Flagging” is natural pruning. Now that the high-pitched din of cicadas is gone, you may have noticed brown tips on the branches of many of our trees. For the mature trees in our neighborhoods, this is no cause for alarm.

The 17-year cicadas began emerging in May, crawling to the nearest vertical objects then climbing them to molt, a process taking about one hour. During the warm days of May and early June the chorus of male cicadas could be heard all over College Park, as they tried to attract females.

After mating, female cicadas used their ovipositors (needle-like structure) to insert 400 to 600 eggs in the thin tips of deciduous tree branches. For cicada egg laying, the preferred trees are nut trees, fruit trees, maples, hickory, redbud, hawthorn, black locust, and dogwood trees. In College Park, oak trees are also a favorite. Six weeks after mating, tiny cicada nymphs fall from trees and burrow into the ground, where they feed on tree roots until they emerge 17 years later. The next big cicada event will be in 2028.

Damage to trees occurs when female cicadas deposit eggs in thin rows in tree twigs. Evidence of this damage can be seen in College Park, where the tips of mature tree branches have died, the branchlets with attached leaves turned brown, and dropped to the ground. This cicada-caused pruning is called “flagging.” Older trees will sustain this natural pruning and grow new twigs. Younger trees are more vulnerable and may sustain severe damage. Trees with flagged twigs can be pruned to remove the flagged twigs.

Research indicates that the growth of trees during periodic cicada emergence years is slower than other years. Do not worry, normal growth in response to rainfall amounts will resume next year.

Residents who put landscape netting or burlap cloth around their small trees to protect them from cicada damage can remove the netting or cloth six to eight weeks after the cicada chorus has stopped.

If you would like to more about cicada tree damage, please refer to the following web sites:

• https://www.nrs.fs.fed.us/podcast/
• https://utianews.tennessee.edu/the-17-year-cicadas-can-damage-your-trees/
• https://extension.umd.edu/resource/cicadas nut
• http://bugoftheweek.com/ (Mike Raupp, PhD, UMCP Entomology)
• https://www.purdue.edu/fnr/extension/purdue-landscape-report-17-year-cicadas-are-coming/
• https://mda.maryland.gov/plants-pests/Pages/periodical-cicada.aspx

From the City's Tree & Landscape Board. Photo credit (cover): Ward Upham, Kansas State University.