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Calculation of dose and projected efficacy when using visible or UV light to suppress plant pathogens and arthropod pests

Tyler McCann: Cornell University

<div>Visible and ultraviolet (UV) light can be used to suppress plant pathogens and arthropod pests, but the mode of application may affect result reproducibility. Varying biological efficacy across spectra, preconditioning effects of spectra, impacts of circadian rhythm, and the question of reciprocity likely each affect biological response. The Bunsen-Roscoe law of reciprocity holds that a given dose produces an equivalent response irrespective of intensity and time. Experimental suppression of powdery mildews by UV with dose (joules) applied over a range of intensity (W/m<sup>2</sup>) and time (seconds) was used to examine the impact of reciprocity on lethality. To date no study has shown that reciprocity holds at UV intensities, times, and doses previously reported. The unknown nature of reciprocity could pose problems in translating experimental data to practical treatments for both UV and visible light. We exposed conidia of <em>E. necator</em> to UVC (254 nm peak, FWHM <5 nm) doses of 0 to 200 J/m<sup>2</sup> using multiple iterations of intensity (W/m<sup>2</sup>) over times from 4 to 400 seconds; a range that encompasses many previous reports. Within this range of intensity and time, reciprocity of treatment effects held for all doses that significantly reduced conidial germination (i.e., doses from approximately 20 to 200 J). Ability to reproduce results among diverse studies would be enhanced by the provision of data on spectral distribution, intensity, and duration of application for all experiments.</div>