Charlie
I know. Why do you think I offered to go in your place?
At the very least they probably use unregulated amounts since they don't have the same kind of environmental regulations in place that much of the west has. But even here there could be pesticides in use that aren't harmful to Muggle creatures but hurt dragons. And the Muggles wouldn't know that they're hurting a species that they believe to be mythological.
Which reminds me. Any ideas of who we could approach in the Muggle world that could do something about it if we find out that's what's causing the problem?