Joe and tomatoes

Joe told me off for putting too much Bordeaux Mixture on my tomatoes. I told him I'd measured it carefully according to the instructions, but he said I might kill the tomatoes. I see what he means - it might stop their leaves breathing.
I asked him whether he'd sprayed his tomatoes yet, and he said yes, twice. I hadn't seen any of the telltale blue on them, and he explained that he had started using some ghastly chemical beginning with Di-. My other neighbours are using it too - they nearly gassed me with it a couple of days ago. Mind you, the leaves of my tomatoes are looking very curled. But I need to look into this Di- stuff before I use it.