Can anyone tell me what I should be using to combat whatever is eating away at my dahlias? Pic below...

im guessing its slugs. use whatever means necessary to get them little buggers! haha

Would an ammonia drench help, like with hostas?

I use sluggo or something like it. Bait that I think has iron that the slugs eat and die but doesn't harm beneficial insects.

Sorry somehow I missed these posts when they first went up. Thanks I didn't realize that slugs were doing this. I usually don't have too much trouble with them but I'm well-armed with the right medicine. I will put some out and see if things don't improve. I had mistakenly assumed it was caterpillars had to use some BT I haven't seen any great Improvement.