What is this purple flower usually growing in clusters in pastures or ditches, blooming typically mid to late May?
I cannot be certain from the photo that you sent. I need closeups of the plant itself. The color looks like a vervain, Verbena canadensis now called Glandularia canadensis. If it were earlier and in untilled cropland I might guess purple henbit – Lamium purpureum, but I would tend to go with the Verbena at this time. Both can paint a cropland purple.
Dr. Steven Hill, Botanist, SCNPS