Permanone works well to kill them on clothes. It kills them, not just repelling them. I usually hit the socks and the long pants. Duct tapeing the cuff of your jeans to the top of your boot is added protection. You go around once normally then wind more tape off backwards until you reach full circle, fold a bit for a tab to remove. The chiggers that hit the glue on the duct tape go no where. I've had the tape become light brown from so many chiggers in certain areas of South Jersery.
Avoid any dry grass or thick brush if you can.