It just occured to me that some apartment complexes will fine you for not picking up poop. If the main office or manager is not doing anything about the problem, then turn the tables. Tell them you are going to call the city and report the unsanitary conditions on their property. See if they don't step up to the plate then. I mean you are paying rent and I am sure that groundskeep is apart of what you are paying rent for.
I don't know just a thought! I really don't know if the City will step in but it couldn't hurt to try