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Identification of weather variables associated with epidemics of sugarcane orange rust in Florida

Bhim Chaulagain: University of Florida

<div>Most sugarcane cultivars grown in Florida are susceptible to orange rust caused by <em>Puccinia kuehnii</em>, thus threatening sugarcane production. Currently, Florida’s growers rely on fungicides for orange rust management and application schedules are based solely on disease scouting. The objective of this study was to identify weather variables associated with disease progress in order to develop a weather-based model for prediction of orange rust epidemics. Disease severity (percent rust-affected area of the top visible dewlap leaf) was recorded every two weeks on two to four sugarcane cultivars (CL85-1040, CP80-1743, CP88-1762, CP89-2143) susceptible to orange rust and grown at Belle Glade, FL, from 2014 through 2016. Hourly weather data for 30-day periods prior to each orange rust assessment were retrieved from the South Florida water management district’s weather station, located within one mile from the experimental fields. Two hundred fifty variables were derived from weather data and evaluated as potential predictors of rust severity under field conditions. For all three years of disease observation, the number of hours with an average air temperature of 20.0-22.2°C and RH ≥ 90% from 8 pm to 8 am over the 30-day period prior to disease assessment correlated (r > 0.80) with rust severity. These variables will be used to develop a sugarcane orange rust prediction model and improve Florida’s orange rust management by optimizing the timing of fungicide applications.</div>