Space-Time Variability of Leaf Wetness Duration in Florida.

Leaf wetness duration (LWD) and temperature during the wetness period play an important role in pathogens development. They are common inputs in warning systems to alert disease control, since usually higher LWD implies in higher disease occurrence if temperature is within a tolerable range for pathogens. This study investigated LWD’s spatial and temporal variability in Florida to assess which regions and periods might be favorable to disease occurrence. LWD was estimated based on the number of hours with relative humidity equal or greater than 90% (NHRH≥90%). 3-hourly relative humidity was collected during 1979 to 2010 from NARR dataset provided by NOAA (National Oceanic and Atmospheric Administration). Average monthly maps of LWD, accumulated LWD, and total of days with LWD equal or greater than 8 hours were generated. Results showed low monthly average variability of LWD and accumulated LWD. Higher LWD and accumulated LWD levels occurred at the eastern coast, Panhandle, and southern regions in Florida, varying between 6 and 10 h and 200 to 300 h, respectively, whereas the central-northern region had lower values of LWD, from 4 to 6 h, and accumulated LWD, from 150 and 200 h. Regarding to the number of days with LWD equal or greater than 8 hours, lower number of events occurred from June to December, especially in the central and south regions of the state with values between 4 and 8 days per month. The east coast and Panhandle regions had lower variability across months and higher occurrence of days with LWD equal or greater than 8 hours, between 16 and 20 days per month. The next step of this study is to aggregate ENSO phases information of El Niño and La Niña to better characterize LWD spatial and temporal variability.