Salt or Sugar deposits on leaves.
Salt like deposits on tomato leaves? Look up Sugar deposits on tomato leaves and you will discover the world of psyllids. It looks like fine salt to me too, but in searching the net using the word "salt" or "salt-like" deposits didn't find much but aphids, and I am familiar with aphids. Then I searched for suger deposits on tomato leaves and bingo. Gotta get them early.
I just discovered mine today, and I'm trying Spinosad. We'll see.