What Is Eating My Lettuce From Underneath?

Identification

• Several species of root maggots damage vegetable crops such as lettuce, radishes, beets and onions. Seed-corn maggots, onion maggots and cabbage maggots all feed on lettuce roots causing damage to the root system. Root maggots reproduce when adults lay their eggs on host plants, near the soil line. Adult root maggots are small flies that resemble common houseflies. After the eggs hatch, peg-shaped legless larvae burrow into the soil and feed on lettuce roots.

Signs and Symptoms

• Lettuce infested with root maggots have brown tunneling scars on plant roots. Injury to the root system interferes with the way water is carried to the plant, causing lettuce to turn yellow and for plants show symptoms of reduced vigor. Heavy infestations can cause crop loss, root rot and plant death.

Cultural Control

• Delaying planting until weather conditions are favorable for rapid germination reduces root maggot infestations. Avoid planting seeds too deep to keep seed-corn maggots from feeding on your seedlings. Spreading diatomaceous earth around the base of your lettuce seedlings may also help keep root maggots from infesting your plants. Row covers placed over seedlings may also be an effective form of control by preventing adult flies from laying eggs on emerging plants.

Chemical Control

• Soil based insecticides may help control root maggots in your lettuce. The University of Kentucky recommends dusting your lettuce plants with malathion when adult flies are present in your area. A variety of beneficial insects such as lady beetles and parasitic wasps feed on root maggots and their larvae, helping control their populations, so avoid applying insecticides when these beneficial insects are present. Killing large numbers of beneficial insects with insecticides can cause an increase in root maggot populations, making them more difficult to control.