Experts and BHG readers answer.
curled leaves on semi-dwarf lemon tree
That's not a disease troubling your lemon, it's citrus thrips. When they feed, these tiny insects cause leaves to distort and curl. To confirm this diagnosis, shake a branch with distorted leaves over a white sheet of paper and look closely for tiny skinny yellow-brown insects. You can kill them with Safer Insecticidal Soap, All-Season Horticultural Oil, or Ortho's Orthenex. The soap and oil are contact killers--they kill by smothering and must come in contact with the thrips to kill them. They leave no residual chemicals on the plant, so it's safe to use them right up until the day before harvest. Please read and follow label instructions.