A site-specific sensor for measuring leaf wetness duration within turfgrass canopies

Leaf wetness is a key factor in the initiation and development of many plant diseases. Measurement of leaf wetness duration in turfgrass requires sensors that do not disrupt the canopy environment and are representative of leaf surfaces. Therefore, a small (5 mm head width) sensor was developed that can be inserted into grass blades with only minor modification of the canopy and can capture the spatial variability of leaf wetness. The sensor detected wetness onset and depletion in a tall fescue turf canopy in the field with an average error of less than 20 min when compared with a tactile method. The sensor indicated leaf wetness over 1 h before moisture was visible and detected wetness depletion 1 h after moisture was no longer visible, suggesting that the sensor is sensitive to microscopic water films. When the sensor was compared with a leaf latent heat flux model in tall fescue canopies, no significant differences between the two methods were found in detecting wetting and drying episodes and in measuring leaf wetness durations. However, the sensor was sufficiently sensitive to record 1 h later wetness depletion (P < 0.01) and 1 h longer periods of leaf wetness (P < 0.01) in a high plant density canopy as compared with a low-density canopy, whereas no significant differences in moisture conditions between the two canopies was found using the leaf latent heat flux model.