By Kirsten Conrad, Agriculture and Natural Resources Agent, VCE
As the Brood X cicada emergence is coming to a close for 2021, we are beginning to see the “flagging” on trees that results from the egg-laying behavior of the females.
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After mating, female cicadas use their ovipositors to cut slits in pencil-sized tree branches (¼ to ½ inch in diameter). They then deposit 10–25 eggs into each slit, potentially laying more than 500 eggs. The slits can injure the branch and in some cases cause the branch ends to die back. Some trees show many dead branch ends (flagging) within weeks of egg laying. Eggs hatch 6 weeks after being laid, and the nymphs then fall to the ground, where they begin burrowing down and attaching to roots. In Northern Virginia, cicada eggs will begin hatching in early August.
Flagging is not serious in mature trees – it is a kind of “pruning” of tips of branches. Young trees have a higher proportion of pencil-sized branches and may have more damage. Trees chosen more often by female cicadas and that more often sustain damage from ovipositing include oak, elm, maple, dogwood, cherry, hickory, ash, chestnut, and some fruit trees.
It is not necessary to prune the branch tips of trees with flagging – dead parts will fall off by themselves. If pruning must be done for aesthetic reasons, try to wait until August 1 or later to do so. Sometimes these branches will survive. Premature removal of the affected branches and disposal of cicada egg-laying sites can reduce the population of cicadas in future.
Careful pruning can rejuvenate some trees that have sustained greater damage by generating new lateral growth, which helps trees recover. If you choose to prune the branch ends, try to leave the part of the branch with the slits that contain the eggs, or if you do cut them, leave the branches on the ground and allow time for the cicada eggs to hatch and the nymphs to drop off and enter the soil.
Brood X is next due to emerge in 2038. Postponing the planting of new trees for 2 years before the emergence of a given cicada brood will protect them from the disfiguring damage that young trees sometimes sustain.
- For more on pruning in summer, including pruning after cicadas, join “Summer Pruning for Woody and Herbaceous Perennial Plants,” July 23, 10:00 – 11:30 am EDT. RSVP here: https://mgnv.org/event/summer-pruning-for-woody-and-herbaceous-perennial-plants/
- More information is available at the Brood X Cicada Resource Page https://mgnv.org/brood-x-cicadas-video/