Cicadas--Loud but Harmless to Plants

Cicadas--Loud but Harmless

Brian Jervis: Ask a Master Gardener

Tuesday, August 8, 2017

Q: It seems like there are so many cicadas this year. Are they going to hurt my plants in any way? GM

A: We have been getting calls in our diagnostic center from people trying to identify these beetle-like insect shells they are finding in their yards and wanting to know what that loud sound is coming from their trees. The shells and the sound are from cicadas, and if you aren’t from Oklahoma, the sheer volume a tree full of cicadas are capable of generating can be unnerving. But for locals, it reminds us summer is here.

There are several types of cicadas. The species we are most familiar with is called the Dog-Day Cicada. These cicadas typically have a life cycle of between 2 and 5 years. The sound you hear coming from the trees is actually the male cicada singing to attract females. The males produce this sound by rapidly beating their wings against their abdomen. On each side of the abdomen, there is a specialized organ called tympana, which increases the sound of this beating considerably. These mating calls have been recorded as loud as 108 decibels, which is about the same sound level as an automobile horn from about 3 feet away.

Once the male’s singing has attracted a willing partner, the female cicada lays her eggs into twigs and small branches using a somewhat saw-like egg-laying structure called an ovipositor. Six to seven weeks later, the small nymphs hatch, drop to the ground and burrow into the soil, sometimes several feet deep, where they live out the majority of their lives growing through several growth stages called instars.

When they are ready, the fully developed cicada nymphs burrow out of the ground at night, leaving an exit hole about the size of a nickel. Once out, they climb up onto a tree, fence or low plant where the adult cicada emerges from its final nymph stage, leaving behind that light brown shell or exoskeleton with which we are familiar. These adults can live 5 to 6 weeks during which the process of finding a mate begins again.

Oklahoma is home to at least 12 species of cicadas, one of which is a periodical cicada whose life cycle is an impressive 17 years, the longest life cycle of any known insect. Most periodical cicadas in Oklahoma belong to what biologists call brood IV and were active in 1947, 1964, 1981, 1998, 2015 and will be back in 2032.

Garden tips

·        Fertilization of warm-season grasses can continue if water is present for growth. Do not fertilize Bermuda or zoysia lawns after the end of August. Do not fertilize fescue lawns until it cools off in September.

·        Establishment of warm-season grasses, such as Bermuda and zoysia, by sodding or sprigging should be completed by the end of July to ensure the least risk of winterkill.

·        Mowing heights for cool-season turf grasses should be at 3 inches during hot, dry summer months. Gradually raise mowing height of Bermuda grass lawns from 1½ to 2 inches.

·        Cucumbers may be bitter this time of year and vines quit producing. This is due to the heat. If you are able to get the vines through the summer, after it cools, they will be fertile again and the taste of the cucumbers will improve.