What you're describing and illustrating in the photo is probably honeydew, a sugar-water-like waste product produced by sap-sucking insects somewhere above or next to where the residue is appearing. (Pollen is somewhat sticky in its own way, but not on this scale, though grass pollen and any other windborne pollen produced this time of year -- oaks have long finished blooming -- is certainly capable of sticking to the honeydew.) Insects responsible for honeydew production can include aphids, leafhoppers, planthoppers and treehoppers, Spotted Lanternfly, and scale.

Few of these would need controlling as most do little damage to the plants they are feeding on, despite the nuisance of the honeydew, which will eventually weather off if we finally catch up on rain. If you aren't certain if a mature tree or large shrub in that area (directly above the honeydew, probably) has a pest problem, you can send us photos of its twigs and foliage (especially the leaf undersides where aphids and hoppers tend to live), or consult with a certified arborist who can inspect the plant(s) in person. Anecdotally, there seems to be a higher-than-average aphid population this year for whatever reason, and Spotted Lanternfly is also becoming more abundant across Maryland (nymphs are out now, though they are small and jump around on various plants), but it's hard to guess what the most likely culprit will be.

Miri