W., I think its important to recognize the root of this behavior. He's 8, and he's asserting some control over his own life. When you're 8, there are plenty of things you can't control- but what you put in your own mouth seems like something you CAN control.
So the issue here is whether you're seeing obedience or rebellion in his other behaviors. Is he defying you and the healthy choices you're making for him, is he testing the waters to see what you'll require of him, or are his tastebuds changing? (The word "gross" is a clue, but his tone will be a clue, too.)
I recommend you read the book "Shepherding a Child's heart" for solid advice on how to tell which behavior he's actually choosing, and what to do about it.
Your husband probably has already talked to him about respecting you and doing what you ask him to do.
Hope this was helpful!!