Potato Review

30 POTATO REVIEW JULY/AUGUST 2021 BLIGHT STRATEGIES S TAYING one step ahead of blight is going to be key to successful control both this year and in the future as new strains continue to evolve. Recent data from the James Hutton Institute illustrates the increasing presence of new more aggressive strains across all potato growing regions. While the samples submitted showed that 6_A1 and now 36_A2 were the dominant strains across the UK accounting for 36% and 29% respectively, the resilience of the uazinam-insensitive strain 37_A2 within the population since its rst identi cation in 2016, remains an issue of concern. Meanwhile the chemistry available to growers is coming under increasing pressure. Getting the better of blight How evolving blight strains will a ect spray programmes this season. Craig Chisholm, Field Technical Manager for potatoes at Corteva Agriscience, says the ever-evolving threat of infection needs to be met head-on by growers planning and executing e ective spray strategies using all the tools in the box. Craig said: “At rst sight there appears to be an abundance of riches in the portfolio of blight chemistry but, in reality, it’s not as simple as the number of products available, when it comes to designing a blight strategy. “Resistance to some active ingredients means they are e ectively redundant. e phenylamides are one example, while strains with insensitivity to uazinam (33_A2 and 37_A2) limit its e cacy in the programme. “Although mancozeb is still available this season, its availability in the longer term is still to be con rmed and, on going to print, we don’t know how much longer this useful partner active will be available to UK growers.” The threat this season Last season’s improved harvesting conditions resulted in fewer potatoes left in the ground than in the previous year, further helped by a prolonged period of frosts in early 2021 which will have an impact on the potential population of potato volunteers, reducing the threat of blight from that source for the months ahead. At the time of writing, the conditions were ripe for Hutton Criteria to be met, as indicated by AHDB Blightspy, ring Dark skies looming for blight risk Craig Chisholm