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Design of an Acoustical Particle Counter and Its Use in Phytopathological Research. Martin W. Imhoff, Graduate research assistant, Department of Plant Pathology, North Carolina State University, Raleigh 27650; S. R. Coover, research assistant professor, Department of Environmental Sciences and Engineering, School of Public Health, University of North Carolina, Chapel Hill 27514. Phytopathology 71:152-156. Accepted for publication 26 June 1980. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-152.

An acoustical particle counter and rotorod samplers were used to monitor spores of Uromyces phaseoli var. typica on snap bean during the course of four epidemics in controlled environment chambers. In the acoustical counter, airborne particles are drawn through a capillary section of a tubular acoustical element, where particles larger than 5 μm in diameter shed vortices as they are accelerated less rapidly than the surrounding air. Pressure changes caused by these disturbances in the laminar flow cause sound waves detectable with an electret microphone. Acoustical counts and rotorod counts were highly correlated (r = 0.98), with approximately one acoustical count for every 26 rotorod counts. Disease increase as measured by a visual rating scale was highly correlated with both acoustical counts (r = 0.94) and rotorod counts (r = 0.96). Immediate digital readout, simplicity of design, and large sampling volume give the acoustical counter advantages over other particle counting methods for some phytopathological investigations.