A Mist Generator and Environmental Monitoring System for Field Studies on Shothole Disease of Almond. James E. Adaskaveg, Postdoctoral Research Associate, Department of Plant Pathology, University of California, Davis 95616. David A. Shaw, and Joseph M. Ogawa. Former Graduate Assistant, Department of Land, Air, and Water Resources, and Professor, Department of Plant Pathology, University of California, Davis 95616. Plant Dis. 74:558-562. Accepted for publication 19 January 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0558.

A mist generator controlled by a datalogger was constructed to study shothole disease of almond trees, caused by Wilsonomyces carpophilus (Stigmina carpophila). The system wetted leaf surfaces on selected shoots and recorded temperature, leaf wetness, relative humidity, rain, wind speed, and wind direction. The mist generator consisted of a pressurized water source and reservoir, a delivery system, and a datalogger control system that monitored periods of leaf wetness and regulated mist regimes. Conditions conducive to infection of leaves of almond cultivars Nonpareil and Carmel by W. carpophilus were generated in the field by controlling duration of mist bursts, intervals between bursts, and length of time that leaves remained wet. Disease was most severe (3.1 lesions per leaf) when leaves were misted for 3 or 4 sec every 2.5 or 5.0 min for 16 hr overnight at temperatures of 10–30 C (average 14–17 C). Fewer lesions developed with longer bursts of mist (which removed conidia from leaves), longer intervals between misting (which allowed leaf surfaces to dry), or wet periods of less than 16 hr. Infection (averaging 3.5 lesions per leaf) also occurred when two different electrical conductance leaf wetness sensors were used to govern mist intervals during 16-hr wet periods.