Damage from the cicada summer continues to be felt as fall approaches
This summer we’re lucky enough to be book-ended by two cicada emergences: the periodical species in May-June, and the annual species the rest of the summer. “Lucky” may not be your view, but you have to admit that they are fascinating creatures, and boy do they make an impact. The chorusing is just a memory now, and their bodies are recycling into fertilizer, but we’re still surrounded by blatant reminders of just how numerous they were.
Residents are concerned about the brown branch tips on trees across the state. Oaks in particular exhibit quite drastic-looking symptoms. Are the trees diseased, or dying? While some infections cause leaf browning, much of what you’re seeing in recent weeks is due to periodical cicada egg-laying. We call it “flagging” because the drooping leaf clusters are reminiscent of a flag awaiting a breeze.
Since the damage is so visible and widespread, it’s natural to assume this is a disaster for tree health. Rarely do we need to worry, though; trees have been dealing with this for millennia, and older individuals usually take it in stride. Very young trees may struggle for a couple of years until they can replace lost growth, though it’s possible severe damage will kill an unlucky few.
The egg-laying process cuts slits into the bark of
twigs - look for the telltale dashed line of pits or torn wood, usually on the downward-facing side of the twig. These cuts not only interfere with the twig’s water supply, but also make it more vulnerable to snapping in the wind. This is natural pruning, and not much different from human trimming or sapling grazing by herbivores. As with any clipping, it will stimulate growth, though
most tree species will wait until next spring.
The hatching of these eggs is imminent, though this is similarly nothing to worry about. Nymphs emerging from ground-littering twigs probably have it a lot easier than those negotiating a drop from sixty feet (yikes), but either way, they burrow into the soil and dine on root sap for the next 17 years, all but forgotten. You can trim off flagging twigs any time you wish, but consider leaving the debris on the ground near some trees before raking them up in autumn.
Fortunately for them, the early end to the periodical cicada flight dodges the prowling of a memorable predator that’s returned to our skies and soils. You’ve probably already heard the annual cicadas calling, a classic summer sound. For those of you with sandier soil or thinning lawn, you may have also heard the buzzing activity of the ominously-named Cicada Killer wasp.
Yep, they’re huge. That’s bound to alarm some folks. The females need to be big, though, to haul around their bulky prey. Thankfully, they don’t care about us and only have eyes for one thing: females hunt cicadas, and males hunt females (and try to chase other males away). Males might approach you with an over-eager sense of territorialism, but they can’t hurt you. Females will only defend themselves if you accidentally squish them. Either can refuel on flower nectar or tree sap.
While they stay solitary and don’t have a communal nest like hornets or yellowjackets, a number of adults can congregate in choice habitat. For our concerns, that habitat often is sparse turfgrass, and you may see scattered tunnel entrances with soil kicked-out in one direction. If you’d rather not host this particular party, you’ll need to thicken-up your lawn or cover bare soil with mulch or dense groundcovers. Pesticides are not the answer, as they’ll just be back next year because wasps from outside your yard will discover its appeal. Consistently-damp soil is not to their liking and may discourage burrowing, but you need to be careful not to overwater your plants. Ideally, learn to just live with their antics for a few weeks, and then all will be quiet until next year.
University of Maryland Extension’s Home and Garden Information Center offers free gardening and pest information at extension.umd.edu/hgic. Click “Ask Maryland’s Gardening Experts” to send questions and photos.