Cicadas leave their mark: tree “flagging” visible from egg-laying for next brood

by Kate Evans

Residents may have noticed hanging-down clusters of brown leaves on certain trees on their property or have an abundance of brown leaf clusters on twigs and small branches falling to the ground from the ends of tree branches.

The tree damage is the aftermath of the invasion of the Brood X 17-year periodical cicadas, which is now over, and the beginnings of their next generation of hatchlings.

The female cicadas make small longitudinal slits in the twigs of trees to deposit their eggs after mating.  These incisions that the female cicadas make in the twigs may cause those twigs to hang down or break off, according to the West Virginia University Extension Office.

“This damage can be quite noticeable and extensive during years when periodic cicadas emerge in mass within a given area. Although this damage does not affect well-established trees, it may interfere with the growth of or even kill very young or newly planted trees,” WVU Extension officials noted.

“Pruning out and destroying damaged twigs within a few weeks after eggs are laid can help prevent new nymphs from entering the soil,” they added.

Called flagging

The University of Maryland Extension Office website said that twigs with many longitudinal slits from the cicada egg-laying often break off or hang down from trees because the slits weaken the branches.

This branch dieback condition known as “flagging” is now being seen on trees and shrubs where cicada eggs were laid. Dead branches that can be safely reached can be pruned anytime.

“Delaying pruning until the end of August will support the next generation of cicadas developing in branches before they drop down and burrow into the soil.  We will see this next generation of Brood X emerge in 2038,” Maryland officials said.

They also stressed that young or newly planted trees may have their growth stunted or even be killed if the flagging is extensive during cicada brood emergence years. Young or new plants can be protected by netting or a breathable fabric.

University of Maryland Extension officials reassured that this flagging damage isn’t serious and that trees will easily replace the branches that have been broken by the cicadas.

Trees most damaged

Common trees that are most susceptible to cicada damage include oaks, maples, cherry, other fruit trees, hawthorn and redbud.  Cicadas can lay their eggs on more than 200 kinds of trees, according to University of Maryland Extension cicada information.

The 2021 17-year periodical cicadas have completed the adult stage of their life cycle and cicada eggs will hatch from late July to mid-August, depending on location.

When the eggs hatch, the immature cicada nymphs burrow back into the ground where they will remain for the next 17 years sucking nutrients from tree roots before they return to start their life cycle all over again.

The nymphs will mature underground, then dig their way to the surface in 2038, molt into a winged adult, leave behind their exoskeleton and live for two to six weeks to mate and produce the next Brood X generation of cicadas.

Annual cicadas

While the 2021 periodical cicadas invasion is over, annual or dog-day cicadas are emerging from the ground, transforming into winged insects and looking for mates.  They have a two to five year life cycle and emerge in late summer, according to WVU Extension website information.

Annual cicadas have green to brown patterned bodies, greenish wing veins and dark eyes while the periodical cicadas have dark bodies, orange wing veins and red eyes.

According to folklore, it’s six weeks until fall or until the first frost from when you first hear the mating song of the dog-day cicadas.  Some residents reported hearing the annual cicadas a week to ten days ago so it could be an early fall or frost this year, if you believe that cicada behavior can predict the weather.