Development and implementation of a new national warning system for potato late blight in Great Britain (Hutton Criteria)

Data on late blight outbreaks (obtained through AHDB’s Fight Against Blight activity) were used to test the performance of the Smith Period in forecasting late blight disease outbreaks. The Smith Period is a set of temperature and humidity criteria that was developed in the 1950’s and had not been reviewed or modified since its inception. 

Controlled environment experiments were used to refine the temperature and humidity criteria that define risk of infection, using contemporary late blight isolates. The results showed significant levels of infection under drier (less humid) conditions than prescribed by the Smith Period. These findings were used to develop candidate replacement models for the Smith Period. Ultimately, the best prediction outcome was a model that requires two consecutive days with a minimum temperature of 10°C and at least 6 hours each day with a relative humidity ≥90%. This model was named the ‘Hutton Criteria,’ and was launched as AHDB’s new national warning system for late blight in GB in 2017. 

To review the ability of the Smith Period to forecast late blight outbreaks and recommend any modifications to the criteria.