Brood X cicadas surfaced like clockwork this spring. Now they are gone for another 17 years. Here's what I observed about the cicadas and the landscape damage they caused, as well as ways to control other insect problems that may have slipped our minds while our focus was on the cicadas.
Overall, the experience was a plus for our properties. Cicadas aerated the soil as they emerged. In areas where soil surface is visible, you can still count thousands of half-inch holes, less than an inch apart, at the foundations of houses, under trees and across grassy expanses. The greatest number of emergence holes were near woodlands.
After the cicadas emerged, they shed their exoskeletons. They stood on any object they could reach in the open air, such as a tree, a shrub, a flower, weeds, fence posts, walls or the ground. After molting, the insects sat still for a time, while their new wings and shells hardened. Then they blindly flew for the only time in their life, mated, laid eggs and died.
The ear told you where to find areas of high cicada concentration. Parts of the region were shrill, and loud, up to 100 decibels; a chain saw is 120 decibels. Our neighborhood was a high-pitched, heavily damaged area, but I'm still sorry to see the cicadas go. Seventeen years is a long time before we will hear and see their song and dance again.
Dead cicadas and their exoskeletons will add nutrients to the soil, so let them decay where they are. Wildlife and organisms already have done an admirable job devouring cicada remains, and the damage the bugs caused is now easy to spot.
The earliest damage and twig drop that I witnessed were on box elders (Acer negundo) in May. Their vulnerable young green stems sloughed off, almost unnoticeably, as soon as eggs were laid.
Now, damage to the trees is evident. It appears the hardest-hit trees were oaks; the dead branch tips are numerous.
Dead branch tips can be pruned where it is practical, or, as with the oaks and other large shade trees, you can let nature take its course. Where female cicadas sawed into the branch tips to lay eggs, trees will self-prune as weakened branch tips snap off in storms.
Some trees look bad, but it is easy to clip the trees that have just a few browned branches. We pruned several serviceberries (Amelanchier) to clean them up. In June, trunks of these trees were covered with swarming cicadas. The insects looked like a part of the bark, yet there was little damage. American snowbell (Styrax) was also crawling with the bugs. They climbed up these trees, but preferred not to lay eggs in them. Pruning two to three branch tips is all that is necessary to return these trees to a healthy appearance.
If you are into long-term planning, throw away the branches that you have pruned and raked within three weeks of egg-laying, which would be about now. This will help control the numbers of cicadas for the next emergence, in 17 years.
Hollies, dogwoods, flowering cherries, crab apples, magnolias and Japanese maples were, in most instances, lightly affected. I saw some old specimen cutleaf Japanese maples standing untouched in areas that were thick with cicadas. Elms appeared fairly untouched, as were tulip poplars (Liriodendron). Other large trees that were relatively unfazed were walnuts, ailanthus, catalpas and mulberries.
There is the possibility that the cicadas did lay eggs and injure the bark of thicker stems, but not to the point of killing the branch. Look for vertical cuts along stems about the thickness of your finger. It will still be evident where the wood was sawed into by the ovipositor of the female cicada. The bark will be shaved in narrow strips and appear white. Watch how the branches heal and the broken tips regenerate. Some plants will actually benefit from this kind of tip pruning; it can encourage vigorous, new growth.
Now in July, in gardens that are once again quiet, it's time to get back to the business of controlling some of the more common insects in the landscape. While cicadas were grabbing all the attention, mealybugs, scale insects, Japanese beetles, aphids, gypsy moth caterpillars, flea beetles, cutworms, spider mites, slugs and others were getting a foothold.
Many pests can be controlled by handpicking or washing them off, or by removing all dead or damaged foliage as soon as you notice it. It's not a good idea to use insecticides, because they will kill beneficial insects, too. You can trap slugs with beer in a jar lid or kill them with iron phosphate, a safe material that adds nutrients as it kills slugs. It's sold as Sluggo or Escar-Go. Discourage cutworms with plastic or cardboard collars around the stems of plants. Controlled use of horticultural oils or soaps can rid plants of spider mites, adelgids, scale, aphids, whiteflies, mealybugs and other soft-bodied insects.
Horticultural oils and soaps will kill beneficial insects along with the pests. So, while these products are safe for humans, they shouldn't be used as a preventive spray on outdoor plantings.
Spray visible pests only when they are causing irreversible damage, such when as aphids get so dense that they deform buds and new growth or caterpillar infestation becomes so bad that plants can be defoliated in days. These pests seldom cause lasting damage, but when they reach an unsightly level, use horticultural soaps. In less severe cases, natural predators will take care of the aphids and caterpillars.
Soaps are also effective controls for adelgids, whiteflies, mealybugs and other soft-bodied insects. These natural controls are sold under the names Insecticidal Soap Insect Killer by Garden Safe, Safer Insecticidal Soap and others. Ask at your garden center and follow labeled instructions.
Spider mites, adelgids and scale occur on many woody plants. Horticultural oil is one of the best ways to prevent them. Use it only as needed. Don't apply when temperatures are below freezing. Do not spray it on blue spruce. It will turn the needles a muddy color. The products to look for are SunSpray Ultrafine Oil or Volck Oil Spray, among others. Another natural deterrent that my wife uses in the garden with some success is a garlic juice called Garlic Barrier Insect Repellent.
Joel M. Lerner is president of Environmental Design in Capitol View Park, Md. E-mail or contact him through his Web site, www.gardenlerner.com.