Cicada Tree Damage Unsightly But Mostly Cosmetic

     The cicadas are all but gone for the next 17 years, but they’re still making their presence known.
     At first glance, numerous trees throughout town and across the Upper Cape look as if they’re experiencing a very early fall as smaller branches display dried, brown leaves instead of the usual healthy summertime green. The effect is especially visible all along MacArthur Boulevard.
     The brown leaves have nothing to do with temperature, weather or any other seasonal change for that matter. This unseasonable turning is, in fact, the result of cicadas laying their eggs in the trees.
     “Parts of the Upper Cape are just devastated,” said Scott R. Pendergast, owner of the Tree Doctor franchise in West Falmouth and a Massachusetts certified arborist. “Some places will definitely have mortality issues.”
     Female cicadas choose hardwood trees, particularly oaks, in which to deposit their eggs. The cicadas use a needle-like appendage called an ovipositor to cut slashes in smaller branches (up to a half-inch in diameter) in order to lay 10 to 20 eggs at a time. A typical cicada will lay up to 500 eggs.
     The damage caused by the cicadas prevents water from reaching the affected areas, causing the leaves to die off, which in turn impedes the tree’s ability to photosynthesize sunlight.
     Contrary to popular belief, the nymphs do not feed on the branches immediately after hatching. “That’s a misconception,” Mr. Pendergast said.
     The eggs hatch after a period of six to 10 weeks, and the cicada nymphs drop to the ground, where they burrow into the earth at the base of the trees to await their re-emergence as adults. During their 17-year dormancy period, the nymphs feed on the sap in the tree’s roots.
     According to Roberta A. Clark, horticultural educator with the Cape Cod Cooperative Extension, there is very little that can be done at this stage to mitigate the damage as the nymphs have already fallen to the ground.
     However, she added that even had the public acted earlier, pruning the smaller branches in order to save the rest of the tree “would have been prohibitively expensive,” and pesticides would not have necessarily deterred the flying insects from settling on high branches.
     “You’d have to use a contact pesticide right when the cicadas are landing on the branches” in order for such an approach to be effective, Mr. Pendergast said.
     Ms. Clark said she has received numerous inquiries from people concerned about the damage, both via telephone and while on duty at the Barnstable County Fair in Falmouth, “and I try to reassure everyone that 90 percent of the damage is just cosmetic…it looks awful, yeah, but it’s mostly cosmetic.”
     For those few trees facing more extensive and long-term damage, the cicadas are just one factor among many; the trees most at risk of serious damage have already been ravaged by winter moth caterpillars and drought. “We’re unfortunately in the middle of a serious drought,” Mr. Pendergast said. “It seems every place in the state but [the Cape] is getting rain.”
     “There are some trees that are at risk, but I stress they’re in the minority,” Ms. Clark said, adding, “I’ve been pointing out to people that this happened 17 years ago and the trees are still there.”
     Ms. Clark said the full extent of the damage will not be known “until next year when the trees leaf out in the spring.”
     Sometimes, when the damage is significant, the affected branch will fall off, but Mr. Pendergast said there is little danger of larger limbs simply dropping off a tree, even if the entire tree dies.
     “Deadwood doesn’t fall off right away,” he said, “it’s gradual. They just don’t rot and fall off…there’ll be warning signs, and that’s when you can call an arborist to come out and trim the deadwood if you’re worried about branches falling.”