Thrips are very small and hard to see. They are light brown, slender insects, who while in the adult stage will fly to other plants when disturbed. They 'rasp' into the leaves to obtain the plants juices, leaving the leaf distorted, with noticeable scars. Spraying with insecticidal soap will usually solve the problem. Spraying with malathion or diazinon is effective.
Systemic insecticides are sometimes effective.