Field efficacy of Steinernema feltiae for the control of the cabbage maggot (Delia radicum)

The cabbage root fly (Delia radicum) is a major pest in brassica crops in Belgium. In early plantings of cauliflower and other cabbages, larval feeding on the roots causes destruction of the young transplants. To prevent this attack, growers apply insecticides at the base of the plants before, during or after transplanting. As an alternative, biological control by the entomopathogenic nematode (EPN) Steinernema feltiae is explored under field conditions. Within the present research, the effect of different EPN application methods for the control of the cabbage maggot are tested.
Results of semi-field experiments with cabbage plants in the greenhouse showed that a soil drench with 180000 or 370000 EPN/plant, applied after transplanting, could significantly reduce the damage caused by the cabbage maggot. Plant container treatment by spraying prior to transplanting with 180000 EPN/plant provided less control. Spraying the crop row after transplanting with 55 EPN/cm² provided a very low level of control.
Field experiments in 2011 confirm that an EPN suspension, applied as a soil drench at the base of the plant, at a rate of 180000 EPN/plant, can significantly reduce the damage by the cabbage maggot. At least two soil applications seem to be needed to achieve a good control. Furthermore, the results of different field experiments show that (repeated) field spray applications with EPN offer an unsufficient control of cabbage maggots in the soil. Further research will focus on improvements in the method and the timing of the application, in order to achieve more reliable control results.