The tomato leaf curl may have several causes. One is just called tomato leaf curl and it is physiological and is generally caused by stress and it's not really a problem and just looks unsightly. Tomato leaf curl virus is another source of the symptom, which is hard to pin down as the cause as it looks just like the former. A third is herbicide exposure, possibly from drift in the air from someone spraying on a breezy day up to a mile away, but it looks much different than the two aforementioned with very gnarled growth and tight little almost "fiddle head" looking curled new growth and generally spells doom for the plants. Leaf curl and curl virus generally make the leaves sides curl up and look almost like a taco shell. My guess is it may likely just be physiological leaf curl as I'm guessing they may have just been recently transplanted since it's springtime.
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