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if the leaves roll downward, generally on all plants
, with no yellowing or new leaves and no stunting, then it is just a Physiological leaf roll. It is very common symptom, not caused by pathogen. No action is needed.
if the leaves wilt and eventually yellow and turn brown; and if tiny white flies flutter around when distured, then the probable cause is Whiteflies.
You can buy and use commercial yellow traps or make one yourself. To make a trap, paint a piece of 1/4" board with bright yellow paint, attach the board to a pointed wooden stake that can be driven into the soil near the eggplant(s). Mix one part petroleum jelly or mineral oil and one part household detergent, then brush it on the board.
Or, spray the eggplant(s) with insecticidal soap. Be sure to spray the underside of the affected leaves.