Implementing the modified potato blight risk forecasting model in the Republic of Ireland – the New Irish Rules

 

Potato late blight caused by oomycete Phytophthora infestans (Mont) De Bary, is arguably the most important disease of potato in terms of economic losses and environmental and economic impact of the disease management in Ireland and globally. The pathogen spreads rapidly in humid weather in the foliage of potatoes and tomatoes, causing the foliage to decay and the infection of the potato/tomato. Due to the pathogen’s dependence on weather conditions, a number of forecasting methods have been developed to reduce the input of pesticides and fungicides required to control the disease. Blight is of particular significance to Ireland, following the decimation of the potato crop in the 1850s which, among other colonial factors, contributed to widespread famine, emigration and death. Until recently, blight in Ireland has been forecast using the Irish Rules. The model was developed in the 1950s and calibrated based on the sparse meteorological station coverage at the time and lower risk perception by growers.

 

Since then, the understanding of the pathogen’s development and its relationship to meteorological situation has advanced. This has led to the development of a modified open-source Irish Rules model written in R which facilitates improved forecasting and seasonal re-evaluation of the Irish Rules (Cucak et al., 2019). The new method reduces the threshold for relative humidity from 90% to 88% and the initial (sporulation) period from 12 hours to 10 hours, the analysis also showed thresholds for blight epidemics could be changed from 10°C to 12°C. Though risk estimation has increased compared to the previous rules, estimated chemical usage is still lower compared to standard grower’s practice. The new methodology is now referred to as the New Irish Rules.

 

This research presents the implementation of this new blight forecasting model in Met Éireann’s operational infrastructure, ensuring methods for forecasting blight are as up-to-date as possible and are using industry-wide best-practice.

References: 

Cucak, M., Sparks, A., Moral, R. D. A., Kildea, S., Lambkin, K., & Fealy, R. (2019). Evaluation of the ‘Irish rules’: the potato late blight forecasting model and its operational use in the Republic of Ireland. Agronomy, 9(9), 515.