Recent hot, humid weather has increased the risk of potato late blight with Hutton Criteria periods being triggered in several regions in the last few days.
The Blightwatch alert system, hosted by AHDB and the Met Office, has displayed red warnings since June 11 – indicating the highest level of blight threat – just as many crops are reaching the crucial rapid canopy growth stage.
Red alerts have been issued in England for Lincolnshire, Yorkshire, Lancashire, East Anglia and across the West Midlands.
Potato agronomist John Sarup says crops are growing rapidly in most places. “It is sticky and humid, ideal conditions for blight to develop but I have not seen any as yet.”
He advises choosing products to protect new growth such as Infinito (propamocarb) or Revus (mandipropamid).
“Or you can use Ranman but it you use it now there will be less opportunity to use it for tuber blight.
“Spray at intervals of seven days unless you are using Zorvec where it is 10 days, which I am comfortable with.”
Corteva Agriscience field technical manager for potatoes, Craig Chisholm, also highlights latent blight present in volunteer potatoes from fields that were abandoned following a difficult harvesting campaign in 2019 as a threat.
Ben Sykes, who grows processing potatoes near Tadcaster, North Yorkshire, says he has had to spray for blight less than normal by this point in the season (June 16). “It has been quite low pressure until the last 6-7 days when it started raining. But it is high pressure now so we are using good systemic chemistry.
“We are on our second or third spray depending on how forward the crops are. Our most forward crops are on the third spray and more average crops, the second.”
Despite the prolonged period of dry weather, Mr Sykes says most of his potato crops went into a moist seedbed with only the odd field suffering as a result of lack of rain.