Optimizing applications of entomopathogenic nematodes in vegetables: an overview of a four-year research project

Entomopathogenic nematodes (microscopically small worms that parasitise on various insects) are a safe alternative for chemical insecticides. They are used in the biological control of an increasing number of insect pests. Tailored application technology would improve their efficiency in field vegetables. This project concentrated on the application of EPN in outdoor vegetables. Three difficult-to-reach pests were targeted: the leaf-bound cabbage moth in cauliflower, the soil-bound cabbage root fly in cauliflower, and the onion thrips in leek.
To improve the biocontrol potential of spray applications with EPN against cabbage moth larvae adjuvants that slow down sedimentation of EPN in the tank and thus increase the deposition of EPN on leaves, were sought. Furthermore, the effect of adding yeast extract, an insect attractant, to the spray suspension on the biocontrol of this pest was tested. The selected adjuvants, when combined with an adapted spray application technique, did improve the control of the cabbage moth. But the results were not on par with the control results obtained with Bt, another biological insecticide, when this insecticide was sprayed with the same adapted spray boom as the EPN. The main limiting factor for EPN effectivity was low temperature.
Field experiments against the cabbage root fly have shown that spraying the plant trays containing the cauliflower plantlets is the best application method for controlling the cabbage root fly with EPN. But here again an alternative biological control agent, spinosad, showed better control results.
The field experiments against onion thrips showed that Steinernema feltiae (a cold tolerant EPN species) is not effective against onion thrips in leek.
In summary, EPN are not yet the best solution for large-scale control of these insects in outdoor vegetables. More cold-tolerant EPN species, strains or breeding products that more actively search for a host are urgently needed to improve outdoor control results. In the short term, in temperate climates such as Belgium, the most promising research avenue is to study EPN applications against greenhouse pests.