Could be Chiggers. This is the time of the year that they are the WORST

!!
My horse's legs will just blow up after an encounter, and it takes WEEKS to get the scabs off and legs healed. The itch usually subsides in a couple of days, but it takes considerably longer for the scabs/legs to heal.
Sometimes I've had to use TriHist Granuales (prescription), which is like Benadryl for horses.
I REALLY try to stay out of the tall grass around here from late August till about Oct. 1st just b/c they are so bad.
Good luck, Redboy

PS...., I don't know anything about Itch Weed or Devil's Weed, But CHIGGERS, I do, YIKES!