Further experiments on the measurement of leaf wetness

Two experiments on the measurement of leaf wetness are reported. From the results of a previous experiment, a thin (0.28 mm), double sided circuit board sensor was constructed (sensor C). It was compared to the two sensors used in the original experiment, a cotton cloth on a grid network of two independent fine wires (sensor A) and a thick single board painted with gray latex paint (sensor B). As in the initial experiment, sensor A was found to be the superior sensor, while sensor C gave better results than sensor B. Honeydew, the sugary excrement of sucking insects, caused spurious results from sensors B and C, while sensor A appeared to be unaffected. In the second experiment, leaf wetness was measured with the same three sensors in two plots; a plot treated with an insecticide and a non-treated plot. Sensor A was the superior sensor based on the greatest duration of leaf wetness and comparison with visual observations. The hygroscopic nature of the honeydew increased the duration of leaf wetness between the plots by ∼25% as measured by sensor A.