New criteria to replace Smith periods in potato blight forecasting

New risk criteria which it is claimed will "transform" the performance of potato late blight alert systems were revealed at AHDB's Agronomists' Conference in Peterborough this week.

Image: Scot Nelson (CC BY-SA 2.0)
Image: Scot Nelson (CC BY-SA 2.0)

Baed on research at the James Hutton Institute (JHI) and funded by AHDB Potatoes, the "Hutton Criteria" mark a significant advance on current methodology for predicting blight pressure, known as Smith Periods, now 60 years old.

AHDB Potatoes knowledge exchange manager Claire Hodge said: "Smith Periods have been immensely valuable in assessing blight risk to date. But we need to continue to optimise in response to changes in climate and developments in technology and the Hutton Criteria provides that timely enhancement."

Late blight, caused by the pathogen Phytophthora infestans, remains the single most important disease for the British potato trade.

Agronomist and specialist potato adviser for SPUD Agronomy John Sarup said: "It’s a concern for potato growers every single year and a tool for identifying high risk periods of disease development is crucial to help us protect our crops and give us the confidence to schedule control activities at the right time, to the right level.

"However in recent seasons, blight has been found on crops even before any conventional Smith Periods had been recorded, meaning the current tools and systems just weren’t reliable enough to support precise decision making."

The JHI research examined relationships between reported outbreaks and recorded Smith Periods, and performed controlled environment experiments to determine new thresholds indicative of high blight risk.

When the findings were tested against over 2,000 historic reports of potato late blight outbreaks, the Hutton Criteria demonstrated a significant overall improvement in performance compared to the Smith Periods.

AHDB’s Fight Against Blight (FAB) campaign continues its free alert service for levy payers and aims to incorporate the research findings next year.

Previously, a Smith Period was defined as two consecutive days each with a minimum temperature of 10°C and at least 11 hours of relative humidity at or above 90 per cent.

The Hutton equivalent retains the temperature criterion but reduces the relative humidity threshold to just six hours at or above 90 per cent.

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