Evaluation of spinning disc technology for the application of entomopathogenic nematodes against a foliar pest

Two spinning disc spray application systems, the Micron Herbaflex and Micron Ulva+, were assessed for their potential for the application of infective juveniles (IJs) of entomopathogenic nematodes (EPNs) against larvae of the diamondback moth (DBM), Plutella xylostella. The effect of initial concentration of IJs on subsequent infection was examined for three species of EPNs: Steinernema sp. (M87), Steinernema sp. (SSL85), and Heterorhabditis sp. Increasing the concentration of IJs generally resulted in a significant increase in both DBM mortality and the mean number of nematodes per larva following spray application with the Micron Herbaflex sprayer. Application with the Micron Ulva+ was examined using two different initial concentration of IJs, which generally resulted in an increase in DBM mortality and intensity of infection. The effect of changing the flow rate to the Ulva+ was also examined. This generally resulted in increased DBM mortality as flow rate was increased but there was little change in the mean number of nematodes per host larva. The effect of addition of a number of adjuvants to the spray solution on subsequent infection showed that DBM mortality by the IJs was not significantly affected but that the mean number of nematodes infecting was significantly enhanced by some of the adjuvants. Desiccation survival studies with IJs of Heterorhabditis sp. following application with both sprayers onto Chinese cabbage leaf discs, with or without the addition of an adjuvant, showed that the survival time of 50% of IJs was over 3 h. Infection of DBM larvae was also assessed following desiccation on Chinese cabbage leaf discs. High levels of infection were attainable, in terms of resultant DBM mortality, for at least 150 min following spray application.