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Leaf Surface Electrostatics: Behavior of Detached Leaves of Beans, Maize, and Other Plants Under Natural Conditions. C. M. Leach, Professor, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331; J. D. Apple, graduate research assistant, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331. Phytopathology 74:704-709. Accepted for publication 1 March 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-704.

To determine if leaves become charged under natural conditions, the electrical fields associated with leaf surfaces of beans (Phaseolus vulgaris) and maize (Zea mays) were measured over periods ranging from 1 to 5 days during both fine and unsettled weather. Electrical fields were measured with an electrostatic sensor (field mill) positioned 10 mm above adaxial leaf surfaces. Surfaces of leaves became charged, with average field intensities <500V cm- 1. The highest field intensity measured was 1,600V cm- 1. The size of electrostatic fields appeared to relate directly to changes of humidity and was also influenced by intensity of solar radiation. As relative humidity decreased, field intensities increased; conversely, as humidity increased, leaf surface charges were dissipated. Highest field intensities were recorded on warm, sunny, and dry days, and wind apparently had no effect. At night, when the humidity was high, leaves remained uncharged. During cloudy periods with rain, field intensities were small or nonexistent. Polarity of leaves was consistently positive on sunny, dry days; but on several cloudy days with intermittent rain, leaves were of mixed polarity and predominantly negative on one occasion. A direct comparison of electrical field intensities of beans and maize leaves over several 3- to 5-day periods revealed essentially identical behavior. Detached leaves of eight other plant species were also electrically charged under sunny, warm, and dry conditions. Field intensities for the eight species ranged from 100 to 400V cm- 1, all with positive polarity.