Influence of El Niño Southern Oscillation (ENSO) on Tomato Late Blight Incidence in Mozambique.

Diseases are always influenced by weather conditions, which vary with time and space. This variability causes difficulty for growers in timing fungicide applications. The El Niño-Southern Oscillation (ENSO) phenomenon is the main driver of climate variability in Mozambique and it may influence plant disease occurrence. The objectives of this study were i) to determine the risk of late blight (caused by Phytophthora infestans) occurrence in tomatoes in Mozambique; ii) to determine how ENSO affects disease pressure in the region; iii) to create an AgroClimate tool to optimize fungicide application and improve crop disease management. The probability of disease occurrence was determined using the late blight infection potential index, which uses weather information (daily temperature and rainfall) to predict inoculum increase of P. infestans. The first application date, the total number of applications and the percentage of days with weather conditions favorable for late blight was determined. Due to limited historical weather data availability from in-country weather stations, daily grid-based information from 1983 to 2015 from the Climate Forecast System Reanalysis (CFSR) and Famine Early Warning System NET (FEWS Net) were used in this study. Preliminary results indicate that crops planted from February to April are exposed to higher disease pressure due to rainfall occurrence and ideal temperature for disease development. From October to February, temperatures are excessively high and the probability of late blight incidence was low. Rainfall amounts from May through September are normally close to zero causing low risk for disease development. ENSO has a strong influence from February to May. During El Niño, temperatures are higher and rainfall lower, causing less favorable conditions for disease development whereas the opposite is expected for La Niña. The results of this study will be available on the AgroClimate Mozambique website to inform growers and extension agents and help improve late blight management in the region.