The first step is to check how widespread the problem really is, as there may not be many people that are actually reading the blog or website. You may also want to offer the owner the chance to submit their posts to the association's official website, which gives the board some amount of control yet also makes it apparent that the association allows owners the opportunity to express their feelings.
One of the best options is to make sure you always communicate openly with owners, as a great deal of these problems start when owners don't feel like they're getting enough information, often related to a single issue in the community. Respond to complaints and provide truthful information to owners to combat this problem. Always do your best to stop negative information and outright lies by spreading the truth, either by responding directly to comments or posting the information on the association's website.