If they've already blossomed this is normal condition of plants. They'll continue to die back until fall, when they will regenerate in preparation for winter.
If your poppies are the opium poppy (illegal to grow here in the U.S) then the substance is probably opium tar, which is usually harvested in the Middle East...
If all this isn't a description of your problem, and the flowers haven't yet blossomed then I'd check the undersides of the leaves for mites...



