Periodical cicadas

About

Black cicadas about 1 1/2 inches long, with red eyes and orange-veined wings, that come out of the ground in huge numbers only once every 13 or 17 years in eastern North America. They don't bite or sting, but females slit young twigs to lay eggs, which can badly hurt young fruit trees.

Spotting it

Damage

Females cut slits 1/8 to 3/8 inch long in thin, smooth twigs and lay eggs inside. The weakened twigs break, and their leaves wilt and turn brown, which is called flagging. Mature trees take this as a natural pruning, but young or newly planted trees can be stunted or killed, and damage to young limbs meant to become main branches can hurt the tree for years.

How to find it early

Find out whether a brood is due in your county; Extension offices publish emergence years (for example, Maryland's Brood X returns in 2038). The loud chorus of singing males is your signal that egg laying will start within about 10 days. If you've lived in one place 13 or 17 years without cicadas, you're unlikely to get them this year.

When

Emergence years only: mostly May and June, for about 6 to 8 weeks

Life cycle

Nymphs live underground for 13 or 17 years, feeding on tree roots, then come out together in spring once soil 7 to 8 inches down reaches about 64°F. Adults live 2 to 6 weeks; egg laying starts 7 to 10 days after males begin singing, each female lays 400 to 500 eggs, and the eggs hatch about 6 weeks later and the young head underground.

What to do, gentlest first

Start at the top. Sprays are a last step; always read and follow the product label.

1. Time planting and pruning Prevent

   If an emergence is coming, wait until it's over to plant new fruit trees. On trees under 4 years old, put off winter pruning until summer, after egg laying, so you can prune out damage at the same time.

2. Prune off flagged twigs By hand

   Cut off and destroy damaged twig tips after most eggs are laid but before they hatch, within about 4 to 6 weeks after egg laying.

3. Net young trees Barrier

   Cover young trees with netting that has holes 1/4 inch or smaller, such as mosquito netting, tulle or floating row cover, when the first males start singing. Tie it loosely around the trunk below the branches or pin the edges to the ground, and hold it off the branches with a frame. Remove it when the males stop calling, about 6 to 8 weeks after the cicadas come out.

   Bird netting has holes too big to stop cicadas. Leaving netting on too long can slow growth, cut air flow and block pollination.

4. Insecticides (not recommended for home trees) Conventional spray

   Maryland Extension says insecticides do little to cut cicada numbers or damage, and netting works better. Illinois Extension's spray guide is for commercial orchards only and says homeowners with a few trees should not spray.

   Pyrethroids are highly toxic to bees and can set off mite outbreaks by killing the mites' predators. Some guides mention neonicotinoids; skip them, because they are highly toxic to bees and turn up in pollen and nectar. If you spray, read and follow the label and the pre-harvest interval.

Plants it goes after

Apple (backyard tree), Cherry (sweet and tart)

Pressure by region

Periodical cicadas live only in eastern North America (UConn), and Colorado State says they don't occur in Colorado and are mostly east of the Mississippi River, so western regions, Alaska and Hawaii are rated absent. The 17-year broods are mostly northern and the 13-year broods mostly southern and midwestern. The south-central and Great Plains ratings are estimates. Even within the range, damage happens only in years when a local brood emerges.

Ratings come from extension sources where available; some are estimates, as noted above.