Testing the Accuracy and Precision of Wetness Sensors in a Tomato Field and on Turfgrass

Measurements of dew-period duration by painted, flat-plate, electronic wetness sensors at the top of the plant canopy in a tomato field and on adjacent turfgrass were compared with visual observations. The response range of sensors during the onset of dew sometimes exceeded 5 hr. but was less than 1 hr. on other nights. Sensors in the tomato field indicated dew formation occurred as much as 2 hr. earlier or later than dew became visible on adjacent tomato leaflets at the top of the crop canopy. A calibration threshold for sensors derived from a drying curve resulted in the underestimation of dew-period duration by up to 3.8 hr. and was less accurate than an empirically chosen threshold. Dew duration measured by sensors at the top of the tomato canopy and on adjacent turfgrass deviated from visual observation of dew duration at the top of the tomato canopy by about the same amount of time (0.8-hr. difference). These findings emphasize the need to use properly calibrated sensors for dew-period measurements and to calibrate dew-period measurements in a crop canopy