It is hard to tell from your photos what you have.  It looks like a  concrete box or boxes possibly from an old septice system.  If it is concrete, I would suggest that you contact DNREC.  They may have on file where the old tank and field drains use to be.  If it is plant, insect, or disease related, please provide a better photo along with more information.  Thank you for contacting the Delaware Cooperative Extension Service.