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Protecting your plants from cicadas

A periodical cicada
UI Extension

It's a big year for periodical cicadas in Illinois. Two broods XIII and XIX are emerging at the same time, the first occurrence of that happening since 1803. The cicadas are starting to show up in central Illinois. While the noise they make can be a nuisance to some, they can also cause problems with certain plants.

While cicadas don't eat plants, they can cause damage making small cuts in branches to lay eggs. That can open trees up to pathogens and other pests.

"These damaged areas may sometimes break, which will cause everything past this damaged area to die. This is often referred to as flagging," horticulture educator Ken Johnson said. "Fortunately, this will not kill healthy, mature trees. The same can’t be said for small trees and shrubs, though."

He said the new planted trees and shrubs may have trucks small enough for the insects to lay eggs inside and, if that happens, the trees can die or be seriously damaged.

The U of I Extension offers some tips to avoid problems in your landscape:

  1. Avoid planting trees and shrubs the year before a periodical cicada emergence. Avoid planting trees and shrubs in the spring of an emergence year, too. If you do need to plant, choose plants that have a stem diameter of at least 2½ inches in diameter.
  2. Place netting around small trees and shrubs (up to 10 feet tall), making sure it is secured around the base of the plant to prevent cicadas from crawling up the plant from the ground. The opening should be no larger than ¼ inch. It may be helpful to build a frame around the plants, cicadas may still be able to lay eggs on branches that are touching the netting. 
  3. Twigs and branches that have had eggs laid in them can be pruned off to prevent the nymphs from reaching the ground and feeding. However, feeding by cicada nymphs does not seem to be harmful to the trees they feed on.
  4. Insecticides are not recommended to manage periodical cicadas in home landscapes. Large, healthy trees are able to survive egg-laying with no long-term impacts (this has been happening for thousands of years). Insecticides are not as effective in protecting smaller trees and shrubs from cicadas as netting. Additionally, applying pesticides to control cicadas may harm other organisms, including animals that eat cicadas.
  5. Cicada killer wasps won’t be of any help either. They emerge later in the year when annual or dogday cicadas emerge, and by that time, periodical cicada adults will be dead.

What about mowing? The pest control company Ortho says to consider mowing in the early morning hours or at dusk when temperatures are cooler and cicadas are less active. Cicadas may mistake your mower or other loud tools for a mating call and flock to you.

You may also want to cover your head if you’re going outside where there’s a cicada swarm. Cicadas like to get high up to lay eggs and eat tree sap, and they aren’t too particular about waste disposal. Wear a hat and other protective clothing to keep cicada droppings off your head, it added.

After the adults emerge, they are white, soft, and squishy but will darken and harden overnight, Johnson said. Male cicadas will start singing four or five days after they emerge. They sing to attract females and species has a distinctive song.

After about a month, the adult cicadas will begin to die. Large piles of cicadas under trees can produce a rotting smell. However, as they break down, they help fertilize the soil.

Johnson said six to ten weeks after they are laid, the eggs will begin to hatch. The tiny cicada nymphs will drop to the ground and begin feeding, often on grass roots. Over time, they will dig down into the soil, 8-12 inches deep, and feed on tree roots for the next 13 or 17 years.

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