Very hard to tell by the fuzzy pic, but could be Septoria leaf spot. If so, lesions usually have small black specks in the middle. A number of fungicides are available. Other measures are to limit overhead irrigation (use flood) and if you can, don't plant tomatoes in the same location year after year. At the end of the season, do not compost, but rather, destroy diseased plants.
hortster

Thanks. No black spots, just irregular dry-looking areas on the leaves. I've sprayed Serenade, and I don't water in a way that wets foliage.