What is the Hutton Criteria?
The Hutton Criteria is the national warning system for potato late blight in Great Britain, developed by the James Hutton Institute with AHDB. A high-risk Hutton period occurs when two consecutive days each have a minimum temperature of 10°C and at least 6 hours of relative humidity at or above 90%. It replaced the older Smith Period and is used by BlightWatch and AHDB Fight Against Blight.
This tool applies those thresholds to hourly forecast and recent weather for your location. Because it uses forecast data on a ~11 km grid, treat it as an early indicator: a forecast Hutton period is a prompt to check your spray programme, and a recent one means infection conditions have already occurred.
Disclaimer: Indicative guidance only, based on forecast weather. It does not account for crop variety resistance, local inoculum, irrigation or microclimate. Always follow product labels and consult the official AHDB Fight Against Blight service and your agronomist before making spray decisions. Hutton Criteria definition: BlightWatch / IPM Decisions. Weather data from Open-Meteo.