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Arable

Get it right with blight

With a new and more aggressive blight strain showing resistance to a commonly used fungicide, growers will have to be on their guard more than ever this season.

reasonable price. “That said, it’s important to use as many different actives as possible in a programme as there’s no doubt resistance is a big threat,” he added.

New active

A slow start to the potato planting season has put growers on the back foot, but the advice regarding protection against blight remains the same, writes Dominic Kilburn. A robust blight fungicide programme must be planned, and executed, for the duration of the potato-growing season if crops are to remain protected and blight free by the time they are lifted later this year, says a Norfolkbased specialist potato adviser. With a new and more aggressive blight strain showing resistance to a commonly used fungicide in the UK, growers will have to be on their guard more than ever, ensuring blight spray programme intervals and product choice are spot on. That’s the view of independent agronomist Andy Alexander (right) who says that lessons must be learned following the discovery of the new strain 37_A2. “With some of the first signs of it appearing in crops a couple of years ago, it’s now clear that it is showing resistance to widely-used fungicide

active fluazinam, resulting in tuber blight infection and the breakdown of crops in store,” he explained. “However, I do think that its subsequent spread is due, in part, to some growers taking their eye off the ball with their crop protection programmes,” stressed Mr Alexander. Of primary importance is that blight control programmes begin at the first rosette stage of the crop and continue, without break, until past desiccation, he said. “Growers must apply a robust programme and it is key that they maintain a seven day interval right the way through. “Often you will find some will stop once they have desiccated but they must keep the protection up, particularly as there is less curative chemistry available. “With a £6,000/ha crop in the ground – you have to protect it and for the sake of an extra £50/ha for a

good, robust programme, it’s worth it,” he added. Mr Alexander also highlighted the importance of understanding the chemistry available and how best to target them during the season. “Get the right advice and, in light of the new strain, ensure you understand which actives will provide control of tuber blight. “It’s also important to manage risk through use of the disease and weather forecasting tools available to understand the likely pressure in crops, while control of out-grade piles and volunteers is key,” he suggested. “There will be some who leave fluazinam out of their programmes this season because of the issue with the new strain, but I will continue to use it early in the programme. “Fluazinam has held us in good stead for many years and while it’s easy to have a knee-jerk reaction to news of resistance, it will continue to control other strains and it also comes at a

According to Mr Alexander, new blight product Zorvec (oxathiapiprolin) from DowDuPont is available for the season ahead. “I’ve been aware of this as a coded product for some time now and had a good look at it in trials. It offers a different mode of action to existing chemistry and good protective and curative persistence for mid- to lateseason blight control. “My only concern is that it comes with a recommendation of a 10-day spray interval, rather than 7-, and that worries me a little. “It was used commercially for the first time in Ireland last season and, in time, we will get to understand how best to use it over here,” he said.

Herbicides Turning to herbicides, Mr Alexander reminded growers that although linuron has now been lost from the chemical store shelves, a “use up” period for remaining stocks still exists until 3rd June 2018. “It was the last of the low cost herbicides to be available but there are replacements,” he pointed out. “Praxim (metobromuron) looks like a good pre-emergence product for the control of annual broad-leaved weeds and annual grasses in potatoes. I add Defy (prosulfocarb) to the mix for cleavers control and I’ve been very pleased with it so far. “I’m a great believer in a good preem – crops can take a hit from post-em herbicide use and you shouldn’t have to worry about a post-em if you do a continued over...

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