Effect of ENSO Events on Leaf Wetness Duration during Strawberry Seasons in Florida.

The growth and spread of fungal pathogens are influenced mainly by temperature, and periods of crop wetness, called leaf wetness duration (LWD). For this reason, LWD is a key input to many disease-warning systems. However, LWD data is not commonly available and estimation by mathematical models is an alternative for its use. Modeling also allows the evaluation of effects of climate cycles such as the El Niño Southern Oscillation (ENSO) on seasonal LWD.

The objective of this study was to evaluate effects of the ENSO phases, El Niño and La Niña, on LWD during strawberry seasons in Florida. LWD was estimated using two models: number of hours with relative humidity equal or greater than 90% (NHRH≥90%) and dew point depression (DPD). The period analyzed was from 1979 to 2013 during the Florida strawberry season, November to March. Each strawberry season was classified as El Niño, La Niña, or neutral according to the Japan Meteorological Agency (JMA) ENSO index. Relative humidity, temperature, and dew point temperature were collected from the NARR database provided by the National Oceanic and Atmospheric Administration, which is a grid data with spatial resolution of approximately 0.3 degrees (32km) and temporal resolution of 3 hours.

The total duration of leaf wetness per season, mean LWD per day, and number of days with 8 hours or more of LWD were calculated for Balm, Florida (27.7592° N, 82.2614° W) based on the NHRH≥90% and DPD LWD models. Both models indicated similar trends. During strawberry seasons characterized by El Niño conditions, there was, on average, a larger total amount of leaf wetness, higher mean LWD per day, and also more days with 8 hours or more of LWD in comparison with neutral and La Niña seasons. Strawberry seasons classified as neutral or La Niña resulted, on average, on similar LWD.