THE EFFECT OF PRESSURE DIFFERENTIALS ON THE VIABILITY AND INFECTIVITY OF A BIOLOGICAL PEST CONTROL AGENT

Authors: PATTERSON, J - OSU; Derksen, Richard; OZKAN, H - OSU; GREWAL, P - OSU

Submitted to: ASAE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: 7/30/2001
Publication Date: N/A
Citation: N/A

Interpretive Summary: During the application process, a suspension will undergo pressure drops during passage through the different components of a spray application system. The largest pressure drop will occur as the suspension passes through the nozzle exit orifice into the atmosphere. Results from this study indicated that the magnitude of the pressure differential had an effect on the relative viability of the nematodes and this effect was species dependent. As the pressure differential increased, the relative viability of the nematodes decreased before reaching a plateau of minimum relative viability at high-pressure differentials. Heterorhabditis megidis, the largest nematode in the study, experienced the highest level of damage over the range of pressure differentials studied, followed by Heterorhabditis bacteriophora and Steinemema carpocapsae. To maintain viability above 85%, operating pressures less than 200 psi (1379 kPa) should be used for Heterorhabditis megidis and less than 300 psi (2069 kPa) for H. bacteriophora and Steinemema carpocapsae. All three species, that survived pressure differential treatments less than 300 psi were viable for at least one week and infected wax moth larva at rates equivalent to nematodes that were not treated with a pressure differential. However, as the pressure differential increased the number of viable nematodes decreased, suggesting that the potential efficacy will be reduced when higher operating pressures are used. The results from this study provide basic information for helping to define optimal operating conditions for applying nematodes as biological pest control agent.

Technical Abstract: During passage through the different components of a conventional agricultural spray application system, a suspension will undergo pressure drops. The objective of the study was to determine the extent of damage to a benchmark biological pest control agent, the entomopathogenic nematode, due to the effects of a pressure differential. A French press was used to expose three nematode species (Steinernema carpocapsae, Heterorhabditis bacteriophora and Heterorhabditis megidis) to a series of pressure differentials ranging from 186 psi (1283 kPa) to 1550 psi (10,690 kPa). Damage was quantified by counting the number of living, dead whole, half pieces and quarter pieces of nematodes and by bioassay techniques. As the pressure differential increased, the total number of living nematodes per mL decreased and the total number of dead nematodes per mL increased. The relative viability of the treated nematodes remained above 85% for pressure differentials less than 200 psi (1379 kPa) for H. megidis and less than 300 psi (2069 kPa) for S carpocapsae and H. bacteriophora. In general, the relative viability decreased at pressure differentials above 200 psi before leveling off near 600 psi. For all three species, nematodes that survived the pressure differential were, in general, survived for at least one week and maintained infectivity of wax moth larva at rates equivalent to nematodes that had not been treated. Optimal pressures for applying H. megidis is 200 psi (1379 kPa)and for applying S. carpocapsae and H. bacteriophora are 300 psi (2069 kPa).