An early start to blight control programmes incorporating 5 – 7 day spraying intervals, robust application rates and driving droplets into the crop canopy using the right nozzles are all key to keeping blight under control according to Tiverton based agronomist Matt Alford.

Matt, a former sprayer operator for 9 years prior to joining Agrii in 2008 is now in his 9th year as an agronomist and currently advises on a significant area of potatoes destined for the crisping and chipping markets between North Devon and Somerset.

“ The South West has its own set of unique challenges for growers with a wide variety of soil types and many smaller tree lined fields that create microclimates for a more humid atmosphere which can encourage blight “ he explains.

Like many agronomists Matt is critical of the potential effectiveness of the revised Hutton criteria and does not feel the recent replacement for Smith periods goes far enough.

“With more aggressive blight strains such as Pink 6 and Blue 13 starting to cycle at 7-8C the minimum temperature of 10C set by the Hutton system 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 8C and more than 11 hours at 90% humidity over 2 consecutive days to trigger a blight period or a near miss whilst 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 BBC 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 8C “ he adds.

According to Matt the key foundation in early season blight control is to get some cover on the ridges as soon as any green leaf 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 its 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 2nd spray early in the program 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 6 meter buffer zone on fields with nearby water channels “ he adds.

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 up water rates to around 250 litres /ha, forward sprayer speeds to 10km/h whilst 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 continues.

By June and July and facing a combination of more stable canopy growth with potentially higher blight pressure Matts 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 concludes.