You can blame it on the cicadas, according to Robert Everhart of Everhart Tree Care.
When they emerge from underground every 17 years to mate, Everhart said the female cicada ” ‘etches’ the branch; in other words, she use a barb on her body to carve a groove into the branch and lay her eggs there.”
“This is not a problem for a healthy tree; it will only cause approx. 6 to 18 inches of the branch to die, depending on where in the branch the eggs are laid, Everhart, a certified arborist said. But, he added, “It may have an impact on an unhealthy tree, but that would depend on how many cicadas use it as a host.”
“Luckily, this is not a huge problem in that it only happens every 17 years. It’s a bit unsightly, but there is really nothing that can be done to prevent it. The healthy tree will heal itself, and next year you may notice some dead twigs at the end of the branch, which will likely break off. It is similar to snipping a small length off a branch, as you might do when you prune.”
Everhart added, “If cicadas were around year after year, then we would be talking about a whole different scenario, with a much larger negative impact.”