Harmonious hooves 8 - please help

I really hate this challenge.
Charge and defeat 30 enemies in 5 minutes on horseback
I’m using royler, with +10 attach helmet.
I’m at the reed devil fields but reed scarecrows stoped respawning so now I have non left
Yes I have the reed devil mask in my inventory but still no scarecrow spawns

Where else can I do this challenge? I have completed the entire story quest line.