Potato blight warning in place for Mayo

Potato blight, caused by the fungal-like organism Phytophthora infestans, has historically had a devastating impact on Ireland, leading to famine, emigration, and death in the 1840s.

Over time, methods for forecasting blight outbreaks have evolved, with the recent introduction of the New Irish Rules. Developed based on scientific advancements and changes in potato production systems, these rules provide more accurate predictions and enable growers to make informed decisions about disease management.

Traditionally, blight forecasting in Ireland relied on the Irish Rules, developed in the 1950s. However, field studies and advancements in understanding the pathogen's behaviour necessitated a re-evaluation of the forecasting model. It was discovered that the old model was overly conservative, often missing the onset of outbreaks and failing to provide timely warnings. As a result, the New Irish Rules were formulated, incorporating updated thresholds and parameters.

The New Irish Rules have introduced several modifications to improve the accuracy of blight forecasting. The relative humidity threshold has been reduced from 90% to 88%, while the initial sporulation period has been shortened from 12 hours to 10 hours. Temperature thresholds for blight epidemics have also been adjusted from 10°C to 12°C. These changes reflect the latest scientific understanding of the pathogen's behaviour and its correlation with meteorological conditions. As a result, the New Irish Rules provide more precise risk estimation, enabling growers to take timely and effective measures to control blight outbreaks.

To aid growers in decision-making, Met Éireann has incorporated the New Irish Rules into their forecast systems. This integration has led to the creation of spatial forecast maps for the entire island of Ireland, covering 3-day, 4-day, and 5-day periods. These maps categorize blight risk into five levels, ranging from Very Low to Very High, based on effective blight hours (EBH). By utilizing these maps, farmers can assess the blight risk and determine optimal spraying times, reducing unnecessary fungicide application and saving valuable resources. This not only protects crops but also benefits the environment by minimizing chemical usage.