Spatial Variability of Leaf Wetness Duration in Citrus Canopies

Veronica N. Santillan, Clyde W. Fraisse, Natalia A. Peres, James C. Colee, Amy Cantrell


Leaf wetness duration (LWD) is a key parameter in some disease warning systems and as an input to biological modeling of infection of many plant diseases in crops. The main objective of this study was to determine the spatial heterogeneity of LWD within citrus canopies during summer and winter conditions. The spatial variability of LWD was evaluated in citrus trees in central Florida at 12 canopy positions during Aug. 2008 and Feb. 2009. The analysis of LWD measurements revealed statistical heterogeneity among sensor heights and horizontal positions. LWD was significantly higher (P < 0.0001) at the top canopy compared to the middle and bottom positions during rainy days and no-rain days. The differences in mean daily LWD between top and bottom canopy during a 31-d period of time in the summer were 2.9 and 2.5 h during no-rain and rain days, respectively. The difference in mean daily LWD during a 30-d period in the winter with no-rain days was 2.6 h. The comparison by linear regression analysis between sensors within the canopy and a sensor installed at 30 cm (0.98 ft) over turf grass in a nearby Florida Automated Weather Network (FAWN) station showed that the station sensor provides accurate estimates of LWD at the top of the canopy. These findings accentuate the importance of accounting for the impact of spatial heterogeneity when LWD is used as input to disease-warning systems.


dew, disease-warning systems, dielectric sensor, rain

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Proc. Fla. State Hort. Soc.     ISSN 0886-7283