According to University of California master gardener June Bleile, loopers and armyworms can cause extreme damage to the lettuce crop. Loopers a green in color, and they move by arching their middles up then pushing them forward, like an inchworm or downward dog position in yoga. Armyworms are green to black. Loopers will create holes in leaves, while armyworms stripe the leaves.
Two other possible causes of lettuce mutilations are cutworms or earwigs. Cutworms cut the seedling off at or below ground level and some varieties chew the leaves as well. Earwigs eat holes in lettuce leaves. All of these pests are nocturnal feeders. Checking your plants with a flashlight after dark may lead you to the culprit.
The preferred method of pest management is to hand-pick them off plants on a regular basis. Bacillus thuringiensis, a Gram-positive, soil-dwelling bacterium, commonly used as a biological pesticide, can be used on armyworm larvae, but only when numbers are high.
Earwigs can be trapped in rolled-up newspaper or shallow tuna cans filled with vegetable oil or bacon fat. Place the newspaper or tuna cans near the lettuce plants and check them each morning. Discard the newspaper (bugs and all) once it’s caught earwigs and replace with another paper trap. The can traps can be reused.
Lettuce is a fast-growing vegetable used in salads and many recipes. This vegetable thrives and will grow in a variety of conditions. Depending on your location, your lettuce crop could fall victim to any number of pests that have the ability to damage or even decimate your plants without employing the proper pest management techniques. To prevent this from happening to your crops, equip yourself with knowledge of the most common pests affecting lettuce crops and be prepared to take steps toward abolishing them from your garden.