Potato Review

www.potatoreview.com POTATO REVIEW MAY/JUNE 2020 29 BLIGHT “There’s also a high risk of seed-borne blight, particularly in earlier potato crops.” Fergus Hawkins ➜ March and April will has reduced the risk of volunteers emerging early but growers will be on heightened alert after last summer’s period of signi cant blight pressure,” he said. “But this does not mean that growers should ignore getting on a curative rosette spray prior to the crop meeting in the row. is is good practice.” While current dry conditions mean the threat is somewhat dormant, the potential remains, should weather conditions become more favourable for late blight. “Ensuring Zorvec Endavia is applied at the rapid growth phase will deliver lasting protection through excellent activity on stem blight plus the ability to take out any latent infection in the crop. By moving upwards in the plant, Zorvec will also provide protection of new growth, a useful additional property in indeterminate varieties throughout the season,” Craig added. “Zorvec will ensure the best possible start to any blight programme and the 10-day spray interval will enable e cient use of scarce labour resources at a very busy time for farmbusinesses.” Craig says two applications of Zorvec Endavia over three weeks will enable growers to return to their regular spray schedule while freeing up a day for other critical activities, such as irrigation scheduling. Reuben said blight pressure in 2019 left growers reaching for Zorvec chemistry as the most e ective product in their armoury. He said: “Last year was an excellent test of the technology. We went into a heavy period of blight pressure and our agronomists reached for Zorvec and I haven’t had a single agronomist or grower who has said it didn’t do what it says on the can. at is as good a recommendation as you can get. “I personally think Zorvec saved us from having a costly blight epidemic in 2019.” Dr Ruairidh Bain has been extensively testing Zorvec Endavia at Scotland’s Rural College, SRUC. He says the co-formulation of oxathiapiprolin + benthiavalicarb has proven to be every bit as e ective in controlling late blight at the rapid canopy development phase as other Zorvec chemistry he has worked with. Ruairid said: “When Zorvec Enicade plus amisulbrom was launched ahead of the 2018 season it was quite an easy technical message for farmers because it was such a step up in e cacy, setting a new benchmark. “What we have seen in trials with Zorvec Endavia is the same standard but in a co- formulation rather than a co-pack.” His ndings mirror the EuroBlight fungicide table – the late blight network covering Europe. e Endavia co-formulation scores 4.9, out of 5.0 max, for leaf blight – the same score awarded to Zorvec Enicade + amisulbrom. EuroBlight shows all Zorvec products to have market-leading rainfastness and protection of new growth qualities. In “extremely high” disease pressure at the SRUC Auchincruive trials site in 2018, Dr Bain said Zorvec Endavia delivered robust control and a signi cant length of protection. “Early on our site experienced extremely high disease pressure, and also particularly rapid haulm growth because of the high temperatures. Zorvec Endavia stood up to that when the competitors in the trials didn’t,” he explained. “We also noted that no matter which Zorvec product we have tested there has been a legacy e ect from use during rapid haulm growth. “Applied during rapid canopy, what we saw was a long-lasting dampening down of the epidemic curve which was not the case for the competitor products tested. “It has shown to deliver very good control from the start of the epidemic when growers might not even know there is blight in the crop. “By using a Zorvec product early you are helping to atten the disease curve, which backs up the manufacturer’s advice to use it early, during rapid canopy.” Dominant genotypes Syngenta Technical Manager, Michael Tait, said the evolution of more aggressive genotypes of potato late blight has highlighted the need for robust anti-resistance strategies with all applications. A Euro ns trial in Derbyshire last year to test the intrinsic fungicide activity of blight products, in inoculated and irrigated plots, which were also shown to be infected with the aggressive EU36_A2 genotype, showed mandipropamid with a drift retardant to be the most e ective fungicide against all the blight isolates in the trial, he said. Mr Tait highlighted oxathiapiprolin was not included in the trial, to ful l industry commitments to avoid its expose to resistance pressure with season-long intrinsic activity trials. “ e trial results showed that Revus is inherently active on all blight genotypes present, including EU36_A2,” he reported. “ e priority to learn from the evolution of more aggressive new isolates is that robust treatments can help protect the e cacy of every application in the programme for season-long control.” Mr Tait added that whilst the trial had been inoculated with Pink 6_A1; Blue 13_A2 and Green 37_A2, subsequent analysis by James Hutton Institute showed that EU36_A2, which infected naturally, was the dominant late blight genotype in infected plots. e incidence of EU_36 A2 increased exponentially last season, to 27% of all blight genotypes identi ed in overall analysis of UK monitoring. at was up from 17% in 2018 and less than 2% when rst found in 2017. “It is now recognised that mixing blight fungicides with di erent modes of action in with Revus, i.e., mancozeb or other partner fungicides, would provide a technically sound and cost-e ective option for growers and agronomists,” he said, adding that the mix also ensures growers can make best use of available CAA fungicide group applications under FRAC guidelines. He reminded growers that where CAA fungicides are applied as a mixture, they can be used for up to 50% of the total number of “The priority to learn from the evolution of more aggressive new isolates” Michael Tait

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