You may find holes in leaves or feeding damage from the edge of the leaf surface. Handpicking caterpillars is effective. Insecticides are not recommended. Flea beetles or Harlequin bugs may occasionally appear in large numbers on the leafy vegetables. You will see holes in the leaves and find the insects by careful observation.
Flea beetles are tiny and make tiny holes.
Harlequin bugs are larger, oval-shaped, and brightly colored. Sevin or diazinon provides control. This disease is transmitted by leafhoppers, which hop readily and are very difficult to control. And there is no control for the wilting, yellowing leaves. Pick and discard diseased leaves.