Fear of the Swarm

Fear of the Swarm

Within the past few weeks, we've finally witnessed some consistency among the temperatures we experience day-to-day. They have warmed, telling us summer is near, and, at last, we can breathe a sigh of relief.

But just when we assume summer will wash all our worries away, the creepy crawlies that have burrowed beneath our landscapes for nearly two decades detect that same warmth and emerge, their metallic tin-pan shriek reminding us that our trees might require a bit of extra attention.

Once the ground temperature reaches above 64 degrees, 13- to 17-year-old periodical cicada broods surface from below to breed. We expect a majority of this year's cicada brood - which could contain millions of cicadas that emerge in the same synchronized generation - to affect trees within states along the East Coast. States that predict an encounter with an excessive cicada population include Connecticut, Maryland, North Carolina, New Jersey, New York and Pennsylvania, as well as Washington, D.C.

periodical cicada
Periodical cicada | Photo: Jon Yuschock, Bugwood.com

According to Anand Persad, technical advisor for the Davey Institute, colossal proportions of cicadas are expected to emerge in the Northeast this year. Cicadas have already made their first few appearances along the Southern portion of the East Coast and will soon approach the New England states.

Cicadas avoid crops, pets and humans, but they can cause a lot of damage to trees. Although many plants in your landscape may host cicada infestations, the insect most commonly attacks oak and fruit trees, such as pears and similar relatives.

As cicadas develop underground, they hook onto and feed from tree roots; however, the damage, often miniscule, is not known to kill the roots. "Cicada damage above ground is more detrimental," Persad explains. Once they emerge from underground, female cicadas use their ovipositor - a protrusion on the abdomen - to slit twigs and branches in which to lay their eggs.

"Females can lay 200 to 300 eggs at one time, often distributing different batches to multiple sites on the same tree, which may lead to tree death," Persad says. "They typically target ½-inch diameter twigs near the tips."

cicada damage
A periodical cicada infestation caused branch flagging damage, or browned branch tips, to the bur oak shown above. | Photo: Linda Haugen, USDA Forest Service, Bugwood.com

Several symptoms may determine the presence of cicada populations, which tend to stick around approximately two to four weeks after emerging from the ground. Their escape route, for example, appears as a cluster of six-inch mud tubes shooting up through the ground near the base of a tree. Brown, dead branch tips on otherwise green trees may indicate cicada damage after an infestation has occurred.  "Pruning in the aftermath of cicada damage may help improve the aesthetics," Persad says.

Young trees, which occasionally experience transplant shock as their roots begin to settle into the ground, are particularly susceptible to cicada damage. The smaller the surface area for new growth, the more likely cicada damage is to ultimately kill your tree.

To protect smaller or younger trees from excessive cicada damage, Persad suggests covering them with a breathable fabric. This form of exclusion prevents cicadas from laying eggs on new growth. "Any sort of netting you can place on the tree is the best way to exclude it from cicadas," Persad says. "Exclusion is a better option for your plant and the environment since a lot of product is required to kill cicadas, which are large insects."

cicada damage
Exclusion, such as draping breathable cloths over trees (pictured above), will prevent female cicadas from laying their eggs on twig and branch tips. | Photo: James B. Hanson, USDA Forest Service, Bugwood.com

You can help your trees fight the swarm of cicadas expected to arrive this summer. For example, place additional bird feeders in your landscape to encourage natural cicada predators - most commonly  blue birds, house sparrows and wood peckers - to perch near your trees and then prey on the cicadas wreaking havoc on your property. "Proactively place bird feeders where your youngest, most susceptible trees or shrubs are," Persad explains. "Birds simply need to impair a cicada's ability to fly - or injure one or both of its wings - to deter it from laying eggs on your plants."

Thinking ahead, however, preventive action will help you avoid heavy infestations from occurring in the future. Fertilize your trees to increase their vitality when cicada infestations threaten them. Cover them with netting material when you know a particular population is headed your way. If you're planting new trees this year, choose resilient specimens such as spruces and pines to deter cicadas from attacking your landscape.

And if the swarm's loud chirping noises are distracting you from concentrating on the health of the trees in your landscape, you can contact your local professionally trained arborist for further assistance with cicada control. With a proper consultation, a muted, more peaceful summer might be headed your way.

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