Growers in the Salinas Valley facing poor lettuce-seed germination are usually uncertain about what caused the problem. They often blame the losses on poor seed quality, planting error, irregular irrigation timing or distribution, high salt levels in soil or water, pathogens, and bulb mite or garden symphylan feeding.
Springtails were not on the list, but lately were found associated with poorly germinating lettuce, particularly during February to May in the northern part of the Salinas Valley. Young lettuce seedlings in fields with high numbers of springtails show slow or stunted growth and do not emerge in a synchronous pattern.
It is not clear if springtails collected from the soil are feeding on lettuce and contributing to the irregular lettuce stand. To answer the question, Area IPM Advisor Shimat Joseph documented the ability of springtails to injure germinating seeds of lettuce in the laboratory and field. He also characterized the feeding injury of springtails on germinating seeds and seedlings of lettuce.
“Springtails can feed on germinating lettuce seeds or young seedlings, resulting in a reduction in lettuce growth,” says Joseph of his research results.
In the laboratory experiments, springtails fed on seeds and young seedlings. Springtail feeding allowed the seedling to survive but affected the normal development of the plant.
In the field, Joseph observed that springtail numbers increased when the field was recently irrigated or after a rain event. In the Salinas Valley, before the lettuce seeds are planted, fields are watered deeply and irrigation continues for at least three weeks after planting. This cultural practice, which maintains high moisture levels for seed germination, might favor fast buildup of springtails. In his study, springtail captures were greater immediately after irrigation. Reduced lettuce yield was noted in these fields compared to lettuce fields treated with a pesticide.
Joseph’s study clearly demonstrates that springtails are an important pest of lettuce and are capable of reducing the crop stand. Monitoring is the key to determine the presence and numbers of springtails. Potato slices are typically used to detect the presence of garden symphylans in the field. Joseph determined this technique is also effective for monitoring springtails. Future research will evaluate insecticide application timing and action thresholds.
Growers now know they have another pest to consider if their lettuce seeds are not germinating properly. Joseph’s research will develop an IPM program for managing springtails. He has already identified a way to monitor springtail numbers. Using IPM can reduce springtail numbers and ensure healthy lettuce plants for harvest.