Very soon now, billions of cicadas will be singing in the trees and flying around yards, parks and forest preserves in the Chicago region.
“We’ve already seen a few of the 17-year periodical cicadas emerge here,” said Sharon Yiesla, plant knowledge specialist at The Morton Arboretum, the large tree-focused public garden in Lisle. “We’re expecting the majority of them to become active adults imminently.”
Periodical cicadas are native insects that are harmless to people and pets, and do no significant damage to garden plants or mature trees. To learn more about this year’s emergence of 17-year cicadas, see mortonarb.org/cicadas-2024.
Cicadas will be most abundant in areas with mature trees. New developments and places where there has been soil-disturbing construction in the last 17 years will likely see fewer cicadas.
The only plants that may be vulnerable to cicada damage are young, newly planted trees and some shrubs. “Female cicadas make slits in small twigs and branches to lay their eggs,” Yiesla said. “On a very
young tree, small twigs and branches may be all it has.”
To protect a valued young tree, wrap it in fine-mesh netting to exclude female cicadas. “Get that done as soon as possible before the cicadas have time to mate,” said Yiesla. “You need to protect a vulnerable
tree before the females are ready to lay eggs.” The Arboretum, which has hundreds of thousands of trees, is wrapping only especially important young specimens, including those of rare or threatened species.
The Arboretum does not advise that homeowners use insecticides to attempt to control cicadas. “There are just too many and it would be futile,” she said. Insecticides also can be harmful to beneficial insects
that control other pests.
To wrap a small tree, use commercial insect netting, available online or at some garden centers, or the fine-mesh fabric, called tulle, that is used to make ballet tutus. “Depending on the size of the tree, you may need several yards,” Yiesla said.
The netting must have a fine enough mesh to keep out cicadas, with holes ¼ inch wide or less, and must last for several weeks on the tree. “Don’t use bird netting or other mesh if it has holes that are ½ inch wide or more,” she said. “If your little finger fits through a hole, it’s big enough to admit a cicada.”
Wrap the entire branching area of the tree. It will likely take at least several yards of fabric. Where edges of the fabric meet, overlap them, tuck them under once or twice, and secure the roll with binder clips, clothespins or staples.
Below the branches, gather the netting around the trunk of the tree or the base of the shrub and clip it, staple it or tie it with twine. Make sure there is no gap more than ¼ inch.
At the same time, “Be careful not to tie it so tightly that the rope or twine damages the bark,” she said. At this time of year, with sap flowing, the trunks of trees are widening, so they need room to expand.
Leave the netting on the tree for four to six weeks, until all the cicadas have died. Then remove it promptly, including anything tied around the trunk.
“Once you’ve wrapped up your smallest and most vulnerable trees, there’s nothing more to do,” Yiesla said. “The cicadas will be noisy and may be annoying, but they can’t bite or sting and they will all be
gone in a few weeks.”
For tree and plant advice, contact the Plant Clinic at The Morton Arboretum (630-719-2424, mortonarb.org/plant-clinic, or plantclinic@mortonarb.org). Beth Botts is a staff writer at the Arboretum.
