Lettuce Problems
by Nancy Garrison, former Urban Horticulture and Master Gardener Program Coordinator
| What The Problem Looks Like | Probable Cause | How To Deal With Problem | Remarks |
|---|---|---|---|
| Curled or distorted leaves. Stunted plants. | Aphids. Tiny green, pink or black soft- bodied insects that cluster on underside of leaves or roots. | Thorough, forceful spraying of plants with water will reduce infestation. | |
| Leaves with ragged holes. Leaves with devoured holes bored into heads of head lettuce. | Cabbage looper. Pale green measuring worm (inchworm) with light stripes along back. Grows to 1 1/2 inches long. Alfalfa looper. Dark green with 3 dark stripes along back. Grows to 1 inch long. | Hand-pick worms. | Alfalfa looper is more common along the coast than inland. |
| Leaves skeletonized or almost totally destroyed. Loose webbing between leaves. | Beet armyworm. Color of mature worms (1 to 1 1/2 inches long) ranges from bright green to purplish green. Most common color is light olive-green with dark dotted or lined stripe and two paler stripes lengthwise on back. | Hand-pick worms. | |
| Small holes in leaves, or leaves heavily skeletonized | Vegetable weevil. Larvae (immature weevils) are green, legless grubs 3/8 inch long when full grown. Adults are brown or gray snout beetles 3/8 inch long. Both larvae and adults move slowly and sluggishly. | Because adults do not fly, infestation of new areas takes place slowly and damage is usually spotty. This insect also attacks other vegetables, including carrots, radish and turnip. | |
| Inner leaves of head lettuce black and slimy on edges. | Hot weather | Do not plant lettuce for harvest in warmest months. | |
| Speckles or mottled leaves on head lettuce. Stunted growth. | Mosaic Virus | Buy and plant virus-free seed if available. No practical control after symptoms on plants occur. | Plants showing symptoms near harvest are edible. Plants which show symptoms early may produce no or small heads. |