Exposure to hydrodynamic stresses during flow through a hydraulic nozzle can cause permanent damage to biologicalpesticides during spray application. Aqueous suspensions of a benchmark biological pest control agent, entomopathogenicnematodes (EPNs), were passed through three different hydraulic nozzles (standard flat fan, Spraying SystemsXR8001VS; hollow cone, Spraying Systems TXA8001VK; and full cone, Spraying Systems FL5-VS) within an experimental,opposed-pistons flow device. Computational fluid dynamics (CFD) was used to numerically simulate the internal flow withinthe XR8001VS and TXA8001VK nozzles, and important flow field parameters from the CFD simulations were compared tothe observed EPN relative viability after treatment. Overall, greater reductions in EPN relative viability were observed forthe flat fan (9.5%) compared to the cone type nozzles (<2.8%). The average energy dissipation rates within the exit orificeswere significantly higher for the XR8001VS flat fan compared to the TXA8001VK hollow cone, which was consistent withthe greater reductions in EPN relative viability observed for the XR8001VS. These differences in EPN damage were due tothe distinct characteristics of each nozzles flow field. The reduced flow area of the narrow, elliptical exit orifice of the flatfan generates an extensional flow regime, where it was found that the tensile stresses developed were large enough to causenematode damage. However, with the cone nozzles, the high rotational flow component did not produce hydrodynamicconditions conducive to causing nematode damage. Overall, common hydraulic nozzles were found to be acceptable for sprayapplication of EPNs following the manufacturers recommendations. However, it is recommended that an appropriately sized(i.e., larger than the organism) cone nozzle is more suitable for spray application than a fan nozzle to avoid damage to thebiopesticide.