The resilience of UK potato growers and their advisors is being tested, this year even without Coronavirus.
The evolution of blight strains has added another level of complexity. 36_A2 and 37_A2 are a game changer for growers, as they complete their lifecycle much faster at lower temperatures and produces higher numbers of sporangia per lesion.
Stef Dierickx, Zonal Expert in Potatoes for global agrochemical manufacturer Belchim Crop Protection, has studied the rise in outbreaks of both the 36_A2 and 37_A2 strains in the UK as well as Germany, the Netherlands, France and Belgium. He highlights the devastating effects of the EU_36 genotype can have on crops and advises all UK growers to be on their guard during the current season. “Both these newer strains, but particularly EU_36, cycle so quickly that, if they do get into the crop, they are almost impossible to stop. Even expensive block sprays designed to stop blight in the field will not work in many cases that I have seen.
Growers need to think about building programmes around products with curative activity to block any potential infection from latent infected tubers. During the rapid canopy phase growers must maintain a very strict protection programme employing short spraying intervals and using products at their full dose rates whilst alternating different modes of action. I would also advise inclusion of a curative compound such as cymoxanil in all sprays” he adds.
For later season tuber control Mr Dierickx advises spraying before any forecasted rain (even if it means shortening a spraying interval) so the product is ready to give protection before leaves get wet. “
For late season control the key choice is Ranman Top so it is essential to save 2-3 sprays for the end of the season to help protect against tuber blight. Although 2 other products offer zoospore activity, the key strengths of Ranman Top are its rainfastness and its flexibility in the tank-mix with other products, including pyraflufen products (Gozai, Kabuki or Albis) plus methylated vegetable oil used for desiccation. Ranman Top is also useful if temperatures drop and there is an increased risk of Zoospore activity.
With diquat gone, flail and spray , or chemical-only desiccation will now take slightly longer to completely kill green leaf and stems, increasing the risk of tuber blight, so the blight programme must continue until the end.