The Residents Association is bigger than one person. Write a letter, politely but firmly asking that they refrain from having "their staff" dumping the grass outside your wall. (must admit, I've never head of an RA refer to the landscaper as staff before, but whatever rocks their boat!!) If you can, suggest an alterntative that might be useful. Make lots of noise about Health and Safety issues - the flies etc. Tell them about the conversation with the rep and point out that as a resident of the complex you have as much right as everyone else to the peaceful enjoyment of such.
Just be mindful that these people are your neighbours so a polite and firm letter might solve things without having to threaten or resort to anything more legal.