Do you know any history of the property? I don't like asking this question, but is it possible roundup was sprayed all over? (Obviously not by you). Did you notice any problem when you bought it or did it happen after? Do neighbors treat their yard with something? Usually nature self corrects and only some things are affected, it's highly unusual for all to be affected.
Second thought is to get soil and water tested in depth for more things than the usual 4 tests that come in the homeowners kits.
Otherwise fungus and bug is still possible and as dyzzypyxxy stated, then the County Extension may be able to help.
I feel for you, it's supposed to be fun moving into your new place. I hope you find the answer soon.
