With cicadas emerging this spring, here’s how to protect your trees and shrubs
As the rare dual emergence of the 13- and 17-year periodical cicada broods approaches, experts say some trees and shrubs might need protection ahead of the once in a lifetime event.
Stephanie Adams, The Morton Arboretum’s plant health care leader, said while mature trees should have no problem welcoming the native insects, trees planted in the last five years are likely to have a tougher time.
“Large, mature trees — if they’re healthy and doing well — shouldn't be fazed. Especially for our native trees, this is normal cycling in our environment,” Adams said. “But smaller trees, especially those that have been planted in the last few years, will probably have more damage.”
That damage is presented during the female cicadas’ egg-laying process, in which the insects cut slits into the underside of thin branches to deposit the eggs in. As the eggs mature, the nymphs will drop out of the branch and onto the ground before burrowing into the soil where they stay for the next 17 years.
“Sometimes these branches can be killed by this damage. Because they are smaller branches, the process can essentially strangle them by cutting off all of their vascular tissue so they don't get the nutrients and water that they need,” Adams said.
Heavily damaged twigs and small branches may wilt and break off, according to Adams.
Some injured branches may not die the first year but could weaken and eventually break off in a windstorm.
Species that seem particularly vulnerable to this type of damage include maple, cherry, peach, plum and pear trees. The Arboretum also has recorded damage to rose and service berry shrubs.
In vulnerable trees and shrubs, the cicada slits may not heal and could provide a path for diseases or other problems.
Adams said pesticides are not effective against the cicadas and actually could do more harm than good by killing beneficial insects. She said the best method is to physically create a barrier between the cicadas and the young tree or shrub.
“One thing that we’re doing that has been found to be effective over time is actually buying tulle or bridal veil and surrounding small, susceptible or host trees in it, basically creating a net over the tree,” she said.
Homeowners and landscape managers also can make sure their trees and shrubs are healthy and supported through practices like thorough watering according to soil type and species, as well as applying hardwood mulch.
Adams emphasized the periodical cicadas, much like other native insects, are a natural part of our local ecosystem: Birds and other animals rely on them as a food source, and the bugs benefit the soil when they burrow down into the ground through aeration.
Despite the “yuck” factor, cicadas do have some benefit for trees and plants, Adams said.
Nymph exoskeletons and adult carcasses function as fertilizer as they decay, and carcasses can be composted.
If you’re planning on planting a new tree this year, Adams recommended holding off until early fall or next year. That’s because if gardeners wait until the heat of the summer when the cicadas are done actively laying eggs, that’s not an ideal time for planting trees.
• Daily Herald senior staff writer Mick Zawislak contributed to this report.
• Jenny Whidden is a climate change and environment writer working with the Daily Herald through a partnership with Report For America supported by The Nature Conservancy. To help support her work with a tax-deductible donation, see dailyherald.com/rfa.