If they have no scruples, then they probably also believe in the old adage that there is no such thing as *bad* publicity.
"Bad" publicity puts your name in front of people who haven't heard it before. "Bad" publicity lets people know that someone does the service that they do. "Bad" publicity raises awareness of you in the market place.
The only way this "bad" publicity will hurt them is if existing customers cancel their contracts (which they probably can't). The *bad* publicity is likely to get them new customers. Why? Because not everyone will be sympathetic with the protagonist in our story. There will be people out there who'll say, "This guy was an idiot to plant his vegetables so close to the property line. You know, I need help with my lawn. I think I'll call them."
If you're going to take this into the court of public opinion, before you give the company _any_ publicity, you need to raise awareness about the harm their sprays do, and how the alternatives are less expensive, easier, and more effective. You have to get the court of public opinion to get on your side before you give the company publicity.
As long as there is a significant number of people out there who still believe in better lawns through chemicals, the *bad* publicity you give the company isn't going to hurt them, nor will it help you. It'll do nothing for you, and help them become better known. Free advertising thanks to you.
Before taking anything to the court of public opinion, you need to stop and think about how other people think. There are plenty of people out there who don't think logically. There are plenty of people who have opinions other than you. There are plenty of people who'll get the wrong message unless you know how to spin things right.
You can't just toss a couple of facts out there, and hope people will come to the right conclusion. You must prep them to come to that conclusion long before you reveal the facts of the situation. And in this case, every time people go to the Home and Garden sections of retailers, they see plenty of chemicals. The court of public opinion is being swayed to believe that chemicals are normal. You have to change that nearly completely before your complaint against ChemLawn will gain enough favor in the court of public opinion to actually hurt ChemLawn. A majority opinion isn't enough. Those with the minority opinion are still potential customers for ChemLawn, and your case is not *bad* publicity. It's advertising for them.
Talk to the neighbors. Talk to the company. Report the company to any agency that will listen. But don't take it to the court of public opinion, and don't use that as a threat when talking to the company.
Instead, if you really feel the need to address the court of public opinion, start by showing the benefits of not using chemicals. In a few years, public opinion may shift, and ChemLawn will loose customers. Don't just jump out there and start giving them free advertising now.