Ultimately he backed down and allowed the spraying and in retrospect he admits that was a mistake. Brown is now the state's attorney general, and there's talk that he'd like his old job back. If he wants to demonstrate that he's a real environmentalist, he ought to file suit to block the spraying.
Since that's unlikely, it's going to require an environmental group with the resources and legal support to take this to court. San Francisco's full of them; someone needs to step forward.