Effects of adjuvants on entomopathogenic nematode persistence and efficacy against Plutella xylostella

The effects of spray additives on entomopathogenic nematode persistence and efficacy against Plutella xylostella (L.) were studied. Several adjuvants were toxic to radish seedlings (Raphanus sativus var. capitata L.) but none was toxic to the nematodes or P. xylostella. In the laboratory, the adjuvants that provided the best antidesiccant activity based on a rank score were TX7719, Rodspray oil and Nufilm P. Those providing less protection but better than the remaining adjuvants were 38-F, dextrose and Pluronic F-127. In greenhouse trials, TX7719 and Rodspray oil were more effective than the other adjuvants tested. The stilbene brightener, Blankophor BBH, did not increase nematode efficacy consistently in greenhouse trials probably because the concentration used was too low. In field trials, the combination of TX7719 plus Blankophor BBH increased nematode persistence on watercress leaves (Nasturium officinale R. Br.) and efficacy against P. xylostella significantly. In vitro-produced nematodes benefited more from additives than in vivo-produced nematodes in the laboratory, but that difference was lost in the field. Overall, it was found that additives generally improved nematode persistence and efficacy, but the improvement was probably not sufficient to increase the feasibility of foliar applications of nematodes against P. xylostella. However, further evaluation of adjuvants is warranted for applications of nematodes to watercress for the control of P. xylostella.