Classic blight conditions lead to an increase in Hutton criteria

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WITH Hutton Criteria being recorded across the country, National Influencer for UPL UK & IE, Pam Chambers, gives a current snapshot on potato late blight for June 2019 and potential options for control.

“Here in the Waveney Valley, Norfolk, full Hutton Criteria have been recorded for June 11, 12 & 13, with more forecast for the weekend and beyond. UPL colleagues have also been receiving them in other locations including Staffordshire, so it’s safe to say we are experiencing a strong risk thanks to classic blight conditions.

As a reminder – a Hutton Criteria occurs when a location experiences two consecutive days with a minimum temperature of 10°C, and at least six hours of relative humidity (90%). This methodology came about following research funded by AHDB Potatoes, undertaken by the James Hutton Institute. It’s believed that this is one of the most accurate ways of forecasting potato blight.

This is some contrast to 2018, when disease pressure was relatively low due to the hot dry weather we experienced across much of the season. 2019 is certainly looking like a much higher risk year, so don’t be caught out!

Despite the warm dry weather last year, three newer clones (EU_36_A2, EU_37_A2 and EU_41_A2) increased in frequency. The survival and spread of these clones, when others are decreasing or have failed to establish, suggests they are evolutionarily fit and could prove more challenging to manage.

Wageningen University carried out a number of studies on mancozeb for UPL Europe Ltd and concluded that the fungicide is effective against all strains of late blight, P.infestans. In addition, it’s a critical component of resistance management and integrated disease management programmes for both early and late blight.

A protectant contact multi-site fungicide, mancozeb is available as a ‘straight’, such as Manzate® 75 WG (750 g mancozeb/kg), or as part of a formulated product such as Nautile® DG (680 g/kg of mancozeb + 50 g/kg of cymoxanil). The addition of cymoxanil provides curative properties. The recently updated ‘late blight fungicide table’ from Euroblight provides information on mancozeb and cymoxanil formulations.

Although mancozeb prevents spores from germinating and infecting the potato plant when applied prior to spore release, once infection has occurred and penetrated the leaf, it will no longer control the disease. This means that timing of mancozeb is important, as is the selection of partner actives.

A combination of propamocarb with cymoxanil, such as in Proxanil® (50 g/l cymoxanil and 400 g/l propamocarb hydrochloride), offers excellent protectant and curative properties, which may be crucial this season. With a 14-day harvest interval and a maximum individual dose of 2.5 l/ha, Proxanil can be applied up to four times within a blight programme.

Growers are advised to subscribe to appropriate blight alerts and be as vigilant as ever to help overcome this aggressive disease. Hopefully 2018 won’t have left anyone feeling complacent.”


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