According to the report from the Cape Cod region cited in the UMass Extension
Landscape Message: Aug 23, 2019

"Pests/Problems: Numerous calls regarding sticky black surfaces (sooty mold) have come in over last two weeks. Though sooty mold can occur as a result of a variety of piercing sucking insects, currently it is likely a result lecanium scale, which is widespread in the area. The sooty mold can be found on any structure underneath a tree with a high population of scale. More detail is provided in the June issue of HortNotes see Trouble Maker of Month; https://ag.umass.edu/landscape/newsletters/hort-notes/hort-notes-2019-vol-305"

"Oak Lecanium Scale

The oak lecanium scale, Parthenolecanium quercifex, is a common pest of ornamental trees and shrubs in the eastern US. This soft scale insect (Hemiptera: Coccidae) is primarily a pest on oak but has also been recorded on other species including hickory (Carya spp.) and birch (Betula spp). This insect is very similar to other closely related lecanium scale species, and as such there is often question about their identity as well as whether or not a cryptic species complex exists. Another very closely related insect, the European fruit lecanium or P. corni (also apparently native despite what the name suggests) is found on trees and shrubs in the eastern US and may be confused with the oak lecanium scale."