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area is visible. “This year I will be advising my customers to begin with Kunshi (cymoxanil + fluazinam) – a relatively new addition to the product armoury. It is perfect for coating the ridge while it’s open and delivers a very high dose of cymoxanil at full rate, giving excellent curative kickback. Its partner fluazinam, is proven at the T0 stage and its control of spore activity gives additional protection against blight spores. “On fields where potatoes have followed oilseed rape we also noted Kunshi’s effectiveness on control of sclerotinia during our first full season with the product in 2016,” he continues. Having initially considered Kunshi as a second spray early in the programme last year, Matt now recognises it has a wider role to play throughout the summer and later into the season when higher blight pressure can potentially occur. “A combination of Kunshi + Ranman Top (cyazofamid) gives me the reassurance of a real belt and braces approach but you have to be mindful of Kunshi’s 6m buffer zone on fields with nearby water channels,” he advises. As a former sprayer operator Matt is also keen to highlight the importance of effective application methods that he suggests are sometimes overshadowed by chemical combinations and timings. “When you have massive canopy growth you must

keep water rates up to around 250-litres/ha and forward sprayer speeds to 10kph, while maintaining a 2.5–3 bar pressure, to really drive the droplets into and around the canopy minimising run-off back onto the ridge,” he suggests. By June and July, and facing a combination of more stable canopy growth with potentially higher blight pressure, Matt’s key combinations are Ranman + Kunshi and Ranman + Profilux (cymoxanil + mancozeb), which he always applies at full label rates. “On tuber blight, and in late season, I build my programmes around fluazinam-based products in every diquat mix until the crop is finished,” he adds.

New Hutton Criteria Matt is critical of the potential effectiveness of the new blight prediction system, the Hutton Criteria, with a view that the recent replacement for Smith Periods does not go far enough. “With more aggressive blight strains such as Pink 6 and Blue 13 starting to cycle at 7–8ºC, the minimum temperature of 10ºCset by the Hutton Criteria is not low enough. In my opinion both Blightcast and Agrii’s own Forecast Xtra models are better alternatives. Blightcast pinpoints forecast temperature to hit over 8ºC and more than 11 hours at 90 per cent humidity over 2 consecutive days to trigger a blight period or a near miss, while Forecast Xtra was tuned to the 6_A1 and 13_A2 blight strains several years ago and

is an excellent prediction system which includes data on drops in humidity that are linked to spore release. “I also combine both these systems with Met Office data. If it turns out to be a heavy blight year in 2017 I am sure we will all be saying the Hutton model should have been set at 8oc,” he concludes.

A step up Yorkshire-based SPUD Agronomy’s John Sarup (right) said that while people can argue the difference over the minimum temperature set for the Hutton Criteria, the new system is a step up from the Smith Period method of forecast. “At the end of the day it’s got to be a system that works for everyone, in every part of the country, and while there will always be a variability in requirement from location to location, and field to field, the Hutton Criteria is something that has to try and fit all. “Maybe parameters will change again in a few years’ time, but, for now, the evidence produced by researchers, who have run a large amount of analytics, demonstrates that it’s a better system than we had previously,” he added. John said that the new system would be particularly valuable to him at the beginning of the season, providing him with greater confidence in when to kick-off a blight control programme. “In

the past there’ve been situations when I know I’ve had blight in the crop but there had been no Smith Period warning. It will give me that extra bit of confidence of when to start spraying and, later, whether I need to apply premium products or if I can go with more of a ‘cheap and cheerful’ approach.” According to John, a new blight control product on the horizon from crop protection company DuPont, looks to be of great interest and is set to change how growers fix their spray intervals during the season. Potentially available on farm for the 2018 season, subject to regulatory approval, Zorvec (oxathiapiprolin) is claimed by DuPont to provide a robust 10-day spray interval and have an excellent fit during the rapid growth stage to early stable canopy. “From what I’ve seen of it in trials it looks very impressive compared with other products,” added John. As well as providing a 10-day spray interval, DuPont says that the new product is very active at low dose rates, gives excellent protection and curative activity, is rainfast within one hour and protects new growth. In addition, there is a likelihood that it will have no buffer zone restrictions. Zorvec may also be sold in a coformulation as an anti-resistance strategy, says DuPont. ■

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