A friend makes a rinse out of water & cider vinegar which she puts on her dogs to wash away chiggers. This rinse remains on the coat. Also beneficial for dog's skin.
If allowed to roam; Guinea hens and chickens eat ticks and chiggers. But then you most be around to care for your fowl.
Shortly winter will take care of the chiggers, which are inactive at temperatures below 60oF and die when ground temperatures fall to 42oF.