The garden will be littered with the carcasses of three species of spent cicadas. More ominously, the ends of the branches of shrubs and trees will begin to droop and turn brown.
The female cicada lays eggs in slits she has cut in thin branches. This ensures that the ensuing hatchling nymphs will drop and burrow into soil laced with tree roots, for they feed off the root sap. The egg-laying also means that branches from the point of injury to their tips will probably die back.
On big old oaks or hickories, the resulting branch flagging is unsightly, but it’s a temporary eyesore that the tree will outgrow. But for young, small trees, the dieback can harm the tree’s future and desired shape by pruning twigs destined to become its main branches.
In extreme cases, the wounds can allow disease to move into the tree and kill it. The female cicadas prefer branches that are roughly between one-quarter and one-half of an inch in diameter, and each individual makes several cuts. “For trees planted in the past four years, you may want to consider protecting,” said Stephanie Adams, plant health care leader at the Morton Arboretum in Lisle, Ill. Young redbuds, crab apples and cherry trees are among the types of trees that are at risk.
“It’s the introduced or ornamental species that get hammered by the cicada,” said John Cooley, an evolutionary biologist and cicada expert at the University of Connecticut at Hartford. Fruit orchards and tree nurseries can also see great damage.
It may take a year after the initial damage for the branch to die, Adams said. Cicadas seem to avoid pines and other conifers; the sap is not conducive to egg-laying.
The small-tree damage is a shame, because the cicada is otherwise not only harmless, but its appearance is also one of life’s great occasions, akin to the occurrence of a total solar eclipse or the arrival of a comet in the night sky, but far more tangible. Seventeen- and 13-year periodical cicadas appear in many states east of the Great Plains, but they are staggered from calendar year to year by brood. Next year’s Brood X covers one of the largest geographic areas and is known as the Great Eastern Brood.
For the gardener, the impending reality of this phenomenon poses a quandary. The general advice from horticultural extension agents is to delay planting a tree or shrub in the spring before the hatch, and that advice might also apply to woody plants put in now. Early fall is the optimum period for most tree planting, because it allows the plant to overcome transplant shock and grow some roots before the stresses of the following growing season.
As the saying goes: The best time to plant a tree was 30 years ago, and the next best time is now. Who wants to delay tree planting another year? I would go ahead and plant this year, and take your chances, but with some precautions.
Plastic or nylon netting sold to keep birds off fruit trees and shrubs will do the trick, but only if the mesh size is small enough to keep the cicadas out — something less than half an inch, said Emily Zobel, a senior extension agent for the University of Maryland in Cambridge, Md. Bird netting is typically available from mass merchandisers, garden centers, farm stores, mail-order seed companies and online retailers.
It might be worth obtaining the netting now before everybody gets the same idea next spring, though the product has its issues. One is that it’s plastic, and as an arborist friend points out, the world has enough plastic already. The other is that a sheet of netting needs to be tied together carefully, in a way that keeps the cicadas and other creatures out, especially where it meets the lower trunk. Another is that birds, snakes and other creatures can get ensnared in the netting with horrible results.
Another option is to wrap a tree in the type of fabric row cover or insect barrier that is used for vegetable crops; this avoids the netting trap, though you should pick the lightest-weight fabric you can find for light and air penetration and consider removing it after periods of heavy rain to prevent leaf fungal problems. Some people use tulle or even cheesecloth, but I would be worried about reducing sunlight to the leaves for a month.
Once trees get above eight feet or so, any sort of wrapping becomes an onerous operation, especially if you have to reach for a ladder. And it’s worth knowing that your prized tree may be all right unprotected. Cicada populations can be highly variable, even within the same neighborhood.
If you don’t cover your trees, examine their branches next summer for egg-laying slits and cut out damaged stems. Pruning cleanly to just outside a pair of side shoots will promote branch healing and generate side growth. The twigs you cut off will have dozens — maybe hundreds — of eggs, which you don’t want dropping into the soil around a young tree. The root feeding can also harm trees, arguably more so than the twig damage, because it endures for 17 years. Though, as Cooley points out, native hardwoods have evolved along with the cicadas, and they have learned to live with them.
The one thing you shouldn’t do is reach for some kind of insecticide. “People are always asking us ‘What can we spray?’ and we don’t suggest that at all,” Cooley said. “The amount of spraying you would have to use would wipe out everything. It would be a disaster.”
Apart from killing honeybees and other beneficial insects, a pesticide would poison a cicada eaten by a bird, or a pet.
“I would recommend that if you really want to kill them, use a bucket of soapy water and knock them off the branch,” Zobel said. And while you’re netting, she said, don’t forget to cover your ornamental pond, if you have one. Heaps of decaying cicadas won’t help the water quality.
She said you may also consider a device not available to earlier generations of Americans and Native Americans whose lives coincided with periodical cicada emergences: noise-canceling headphones.
The cicadas gather into mating groups called choruses, and the males try to outdo each other in the cacophonous chirping made from structures called tymbals. The chorus can reach 110 decibels, Cooley said, which is akin to attending a rave party. When you think about it, this approximates what these doomed insects are doing. After they chirp, they croak. Maybe we should rename the Great Eastern Brood the Disco of Death.
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Tip of the Week
Continue to feed houseplants until early fall, but reduce the recommended concentration of liquid fertilizer to ready them for winter dormancy. Pay attention to any insect problems before bringing summer patio dwellers indoors. A simple spray of water will work against aphids and mites. Insecticidal soaps offer an organic treatment for other pests.
— Adrian Higgins