1. History of the prediction of the first epidemic risk date in Sankhu
In 2013, the NPO Agricultural Development Research Institute conducted a field survey for the JICA Grassroots Technical Cooperation Project “Guidance on Optimal Pesticide Use Techniques in Sankhu Village, Nepal 2014-2016”. At the time, the village of Panchkhar, which supplied vegetables to Kathmandu, reported a high incidence of cancer caused by pesticides, which triggered a growing interest in pesticide residue among consumers, and Nepal’s first pesticide residue testing station was established in the Kalimati vegetable wholesale market.
In Sankhu, a suburban rural village located 17 km east of Kathmandu, potato is produced and the fungicide Mancozeb Mancozeb was used to control the blight disease. The disease, called Dharuwa in Nepali, is caused by Phytophthora infestans, a long-lived fungus that has not been eradicated for more than 200 years 1). The fungus multiplies and spreads at a rapid rate, reaching as far as 10 km away. In 2005, the U.S. Environmental Protection Agency (EPA) warned that mancozeb is an exogenous endocrine disruptor that can affect fertility 2). Therefore, grassroots technical cooperation has made it an urgent priority to teach spraying methods to avoid pesticide exposure and to curb the use of pesticides.
For the bacterial blight of potato, there are favorable climatic conditions for infection and growth of the fungus due to factors such as temperatures, humidity, and rainfall; according to Fry (2007), humidity brought by rainfall, condensation, irrigation, fog, and clouds, especially 8 to 12 hours of wet leaf surface conditions, are important. Temperatures as low as 15°C (59°F) and as high as 25°C (77°F) inhibit fungal growth, and according to Perez (2010), temperatures between 15 and 21°C (59°F and 80% relative humidity) are optimal for fungal growth. By utilizing these favorable weather conditions and optimizing the timing of pesticide application, effective pest control measures can be implemented.
Obtaining weather information is a prerequisite for teaching “optimal pesticide use techniques” in Sankhu. Fortunately, since 1971, Nepal Department of Hydrology and Meteorology (NDHM) had been monitoring daily mean temperatures and daily rainfall at Sankhu. Therefore, we used FLABS, a method for predicting epidemic disease outbreaks, to verify favorable weather conditions for epidemic disease outbreaks in Sankhu 3). The results of the analysis suggested that the weather conditions of the summer potato crop were at high risk of epidemic disease outbreak, and that there was room for improvement in the timing of fungicide use.
In this report, we introduce the results of the trial of BLITECAST 4), which predicts the risk date of the first outbreak of the Potato blight using weather information obtained from a field server installed in Sankhu, in order to optimize the use of pesticides, and summarize future issues to be addressed.
1) The potato blight has been etched in history as the cause of the “Irish Potato Famine” of the 1840s.
2) EPA(2005). Its use is strictly regulated in each country, and the European Union EU banned its use in 2021.
3) FLABS is a forecasting system for potato blight developed in Hokkaido, the main production area of potato in Japan, and currently used in Hokkaido and Nagasaki Prefectures; for FLABS methods, see Hokkaido Pest Control Station (2015); for results of analysis using FLABS, see Jun-ichi Yamaguchi (2015, 2016), Agricultural Development Research Association Report (2017), pp. 29-39, see. Note that the JICA Grassroots Project, with the cooperation of a group of farmers in Sankhu, established observation plots on the first day of the epidemic and attempted to observe temperatures, relative humidity, and daily rainfall using a sensor with a memory.
4) University Extension Materials, Inglis (2019), provides concise, easy to understand explanations of the epidemics and forecasting method of late blight occurrence.