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Cicadas and Your Trees

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Fellow tree huggers beware. This is the year of Brood X, also known as the Great Eastern Horde. Soon billions of red-eyed, sap-sucking, bark-slitting creatures will emerge from the earth after 17 years of silence, making their presence known with a vast droning from what seems like every branch. How will your trees survive?

Actually they’ll manage very nicely in most cases. Just hold off on giving those tree hugs, to avoid the creepy-crawlies. Hold off on planting anything with thin branches if you can. And protect your youngest trees.

The three species of orange-and-black cicadas that make up Brood X are less threatening than they look. Widely attacked rather than attacking, they are believed to rely on the evolutionary strategy of “predator satiation,” emerging in such numbers that every bird, snake, cat, and dog in their path can eat their fill without making much of an impact. Cicadas are bent on love, not war, and the buzz the males make, which can get as loud from below a tree as a Harley revving 3 feet away, is a mating call.

To address one common misconception, cicadas are not locusts. Locusts are a type of grasshopper and a swarm of those will do great damage to all vegetation. Cicadas are what entomologists sometimes call “true bugs,” distinguished from most other insects by their sharp beaked mouths designed for feeding on sap (cicadas do not bite or sting, by the way). Cicada feeding habits have never been shown to do notable harm to plant life even though the insects are parasitic, feeding on fluids from grass roots as new hatchlings, tree root sap during their long years as nymphs, and sap from twigs as adults.

Cicada breeding is more of a concern. The insects have been called “nature’s pruners,” as their laying will bring down twigs and thinner tree branches. Female cicadas generally choose pencil-sized branches (1/4″ to 1/2″ in diameter), make slits in the bark, and lay clusters of about 25 eggs. Each cicada lays a total of 400-600 eggs, each egg about the size of a grain of rice. When the eggs hatch, the new cicadas crawl or fall to the ground, often taking the branch with them.

Healthy mature trees do not generally suffer long-term effects even when they host numerous laying cicadas. Newly planted small trees can be hurt or even killed, however, and sick or stressed trees can be further damaged. You can take a number of steps to minimize problems:

  • Extermination efforts are generally NOT recommended given the limited time that cicadas are present above ground and the fact that they will continue to wander in from other areas as well as the danger of poisoning the many birds and animals that feed on cicadas.
  • If possible, simply avoid planting new trees this spring. Cicadas can be expected to start emerging around the start of May (depends primarily on when the soil temperature reaches 64 degrees Fahrenheit 6 inches below the surface, with a warm rain a frequent trigger). They will then be active for about 4 to 6 weeks before dying. Some emerge a bit later than others, meaning that cicada activity may run for a couple of months total, ending by early July. July is not a good time to plant but you will have another window in the fall, as soon as the year’s hottest days have passed.
  • What if you’ve already planted, or are determined to plant, or have young trees planted last fall? There’s no cause for despair. Get yourself some netting to cover the vulnerable branches. The mesh should be 1/4″ (5 mm) or finer to keep cicadas out and also avoid trapping any birds or wildlife. A simple wrap is the “lollipop” method; simply drape mesh over the whole top of a young tree, gathering the netting in toward the base of the trunk and sealing it there and at any other open edges with zip ties, twine, or duct tape. You can also attach mesh to the ground with landscaping staples, for instance if you are throwing the netting over a shrub. Be sure to remove the mesh as soon as the cicadas are gone.
  • You can put foil or sticky tape around the trunks of larger trees to discourage cicadas from climbing up. Unfortunately, however, mature female cicadas can fly on to the tree, so such barriers will be of limited effect.
  • Spraying with a garden hose will work to knock cicadas off trees. You can even pick them off by hand; they are easy to see and to catch if you’re not squeamish.
  • If trees seem to have some underlying problem, have them examined by a licensed arborist. Tree Pros free estimates can help you determine what may be happening. Unfortunately there is little we can do for a young tree with cicada damage, so be sure to take preventive measures.

Before you get to work wrapping trees you may want to assess the level of cicadas in your corner of Howard County. In some spots, especially near big trees that have been in place 17 years or more, as many as 1.5 million cicadas per acre may emerge. But in open land, or land that has been recently developed and raked over by bulldozers, the numbers may be small. 

You can also see if they take an interest in the trees of concern. While cicadas are not known for being picky, they do, for instance, tend to avoid evergreens, disliking the sap. They also relatively rarely target shrubs, typically preferring deciduous trees such as beech, oak, cherry, maple (including small ornamental Japanese maples), and others. You have about a week after emergence before any cicadas begin to lay eggs, so you can see what need there is for netting.

We hope you are able to enjoy the cicada experience, appreciate their summer sound and rare mass presence. You will only experience this force of nature a few times in your life, and are one of relatively few people in the world who has the chance to see it at all. The Brood X 17-year cicadas are limited to parts of 15 U.S. East Coast/Midwest states, with only 3 “epicenters” where numbers truly boom, one of which is the Baltimore-Washington area (the others are in Indiana and around Fort Knox, Tennessee). Watch and listen as the party begins. As “interesting times” go, a cicada invasion could be far worse.

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