Effect of spray application parameters on viability of rhizobacteria used as bio-pesticides in organic fruit production
The biocides, either synthetic pesticides or biopesticides, are applied with agricultural sprayers in form of an atomised spray liquid, being usually a solution or suspension of the control agent, i.e.: synthetic active ingredient, microorganism or extract of naturally occurring material. Prior to the atomisation the spray liquid is subject to a turbulent flow and series of processes taking place in different sprayer components. In the pump the liquid is in turns compressed and decompressed at the frequency of 10-50 Hz (diaphragm or piston pumps) or subject to mechanical rotation at high speeds of 1500-3500 RPM (centrifugal pumps). In the filters the compressed liquid passes the mesh, in the control devices such as valves and gauges it flows at high speed passing sharp edges, and finally in the nozzles it is atomised by mechanical breaking or tearing apart. During all these processes the sprayer components and their working parameters harshly interact with the particles suspended in the liquid and usually they cause an increase of the liquid temperature. The leaving micro-organisms in biopesticides are subject to unfavourable conditions being far from those of their natural habitat. Thus, the question about viability of microbes under these conditions is very important for the efficacy of biopesticides. The objective of this study was to evaluate the survival of two strains of PGPR (Plant Growth Promoting Rhizobacteria), showing potential of application in organic fruit growing, by performing the stress tests simulating spray application process with both the hydraulic and the pneumatic atomisation system.