The Cicadas are Coming!

by Dave Leonard
Posted May 2004

For 17 years little nymphs have been feeding away at the roots of trees all over Kentucky. About May 21 they will crawl out of the ground, disturb our quiet with their mating calls and begin to attack the branches of our young trees with their egg laying.

 This is the year (2004) for a large emergence of the periodical cicada. We have an annual cicada that we hear late each summer, but these insects do very little damage to our plants. The periodical cicada is a darker color and has red eyes. It only emerges in 13 or 17 year cycles and is a real threat to young trees. The females lay their eggs in pencil sized branches. This damage causes the twigs to split, wither, and die. On mature trees you can see dead leaves and broken ends of large branches that we call "flagging". It looks ugly but isn't deadly to a large tree. Small trees planted less than four years ago have many more branches of the appropriate diameter, so flagging can seriously damage and deform them.

 Some of the more favored trees for egg laying include maple, oak, hickory, beech, ash, dogwood, hawthorn, magnolia, willow, apple, peach, cherry and pear. Flowers, vines and shrubs include: Rose of Sharon, rose, raspberry, grape, black-eyed Susan, hollies, spirea, rhododendron, viburnum, junipers, and arborvitae.

What protection do we have from these insects? They have a number of natural enemies but so many cicadas appear at once, that the birds, snakes, and mammals can't eat enough of them to make a difference. If you only have small, newly planted trees or shrubs you can cover them with cheesecloth or netting tied tightly around the trunk for the 4-6 weeks that cicadas are laying. Netting is available at our office.

Insecticides can reduce damage, but homeowners will need to apply them often. The University of Kentucky Department of Entomology suggests using a product with cyfluthrin, esfenvalerate or permethrin. If we have a severe outbreak, even daily spraying won't prevent damage. A more practical approach especially for taller trees may be to call a professional to spray with a product that has more lasting effect, however, they cannot promise you won't have damage.

 It may be possible to prune out the wounded branches before the eggs hatch to limit the secondary damage of the next stage of the cicada life cycle. Newly hatched nymphs fall to the ground and burrow down to the roots where they feed for the next 17 years.

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