Effect of spray volume on the deposition, viability and infectivity of entomopathogenic nematodes in a foliar spray on vegetables

BACKGROUND: Spray volume can influence the amount of free water on the leaf surface and subsequently the ability of entomopathogenic nematodes (EPN) to move. In this study, we investigated the effect of spray volume, viz. 548, 730 and 1095 L ha^-1 on the deposition, viability and infectivity of entomopathogenic nematodes against Galleria mellonella on savoy cabbage, cauliflower and leek.
RESULTS: Increasing spray volume decreased nematode deposition on top of 7.1 cm² leek leaf disks in a 15° angle with the spray nozzle. Although the number of living nematodes observed on leek after 240 min of exposure was not significantly different between the low volume application (548 L ha^-1) and the high volume application (1095 L ha^-1), a greater infectivity was obtained in the latter application. The higher number of droplets deposited on the leek disks in the high volume application probably stimulated the nematodes’ movement. No significant effect of spray volume was observed on the relative deposition of Steinernema carpocapsae on the bottom side of cauliflower and savoy cabbage leaf disks. Despite the low S. carpocapsae deposition on the bottom side of the savoy cabbage disks, high infectivity was obtained against G. mellonella. Using the lowest spray volume on savoy cabbage, infectivity decreased with increasing exposure time, while infectivity was not affected by exposure time when a spray volume of 730 L ha^-1 or more was used.
CONCLUSION: Spray volume is an important application parameter as it affects nematode infectivity. Future research should investigate the effect of spray volume in the field and its influence on the effect of adjuvants.