Spotted Lanternfly doesn't significantly harm trees that are otherwise healthy (at most, they may stress a tree already stressed by other factors that are easier to avoid or remedy, like drought, soil compaction, exposure to lawn weed killer applications, mechanical root damage from digging, etc.). No management is needed, nor would using a pesticide be effective enough while avoiding harm to beneficial insects or other wildlife.

The black residue is sooty mold, a harmless fungus that grows on the sugary excrement (honeydew) produced by feeding lanternflies. If it's an eyesore, it wears off on its own in time, and it does not infect the plant. There is no easy way to remove sooty mold residue forcefully, although sometimes a horticultural oil spray may speed-up the process; note, though, that use of hort. oil may kill beneficial insects that are directly contacted by the spray, such as lady bug larvae, lacewing larvae, and others that can hunt for prey on tree bark. In years with more rain (the past two years have largely been encompassed by drought, which is still present), honeydew may not build up as badly and therefore not support as much sooty mold at one time before it weathers away.

Miri