I also think they’re stressed by this weather, too dry, in Frederick County anyway. We noticed along 15 that most of the Sumac trees have turned. We lost huge numbers of them in that bad drought we had (‘96?).
Upper MoCo here. The black walnut trees are dropping yellow leaves (not unusual at this time of year) and the oak leaves are starting to brown. The weeping cherries are also starting to yellow at the edges. Maples and Redbuds are still green as can be.