14 August 2001
Weather prompts late blight warning

By Tom Allen-Stevens

POTATO growers have been warned to be extra vigilant for blight over the next few days as much of the UK enters a warm, humid spell.

Dr John Keer, potato specialist with distributor Agrovista, told FWi that many ware crops are at a particularly critical stage.

Whats more, there has been a greater incidence of blight in crops over the last few days, which will help spread the disease.

“Late in the growing season, blight can have an even more detrimental effect on ware crops than earlier in the year.”

Heavy rain, such as that experienced in many parts of the UK recently, helps to wash the zoospores through the soil, infecting the tubers below.

“The tubers are harvested seemingly sound, but start to break down in the store from tuber blight,” he warned.

“For ware crops at this time of year, there is a huge danger because growers begin to get complacent about blight.”

And growers shouldnt necessarily hold off spraying until a Smith period is triggered in their area, advises ADAS Nick Bradshaw on potatocrop.coms Blight Watch service.

“This is because the microclimate within the canopy almost certainly extends the duration of humidity and temperature above Smith thresholds.

“Therefore it is likely that conditions will have been more favourable for blight than the Met output indicates.”

The Met Office forecast is for conditions to remain hot and dry, with humid conditions freshening towards the end of the week in the south.

Rain in the north will clear, but conditions across the country will remain unsettled with further heavy showers expected at the weekend and next week.

But Dr Keer notes that the particularly high temperatures forecast for the south east for the next few days will help to limit blight development.

  • Agrovista is holding two potato trials open days at Risby, near Bury St Edmunds on Wednesday 15 and Thursday 23 August. Email john.keer@agrovista.co.uk for details or keep an eye out for the report on FWi.