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Talking Roots with Darryl Shailes: What does this mean in reality for managing blight?

As I write it is raining outside, about 14degC and potato crops are emerging.

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Blight has been confirmed in glasshouses. Plastic and fleece is coming off fields and if any infection is under the fleece the spores can form a spore cloud as the fleece is removed and travel considerable distance.


The 2012 season was the worst blight epidemic year many growers had ever experienced (even worse than 2007) and despite having all the fantastic chemistry we have for disease protection, many fields were completely defoliated by blight. While 2013 conversely was one of the lowest ever for recorded blight infection in fields.


At our Hutchinsons blight trials site - which we run in conjunction with Dr John Keer at RAA – even using untreated areas with inoculated plots and a misting system it was difficult to get blight going in 2013. We didn’t see any significant infection until September. The big difference - the weather.


All of the official warning systems in the UK run on the Smith Period Criteria. Recently other models have been developed in the UK and Holland using more complex mathematical models and incorporating other environmental factors such as leaf wetness and varietal susceptibility.


Also recently we have had a change of potato blight types in the UK. It is thought these new strains have come to our shores from our neighbours overseas.


Blue 13 and Pink 6 are well known and more recently Green 33 has been discovered. We don’t really need to know too much about the genetic makeup of these different strains. What we do need to recognise is that they are fitter and more aggressive and can infect potatoes in a wider range of environmental conditions than first defined by a classic Smith Period. Also they can demonstrate resistant to some active ingredients, including metalaxyl.


What does this mean in reality for managing blight? It doesn’t mean we get blight come-what-may, as demonstrated by the lack of infection in 2013. But what it does mean is that blight is more able to infect potatoes in a wider range of weather conditions and we must react accordingly.

Blight programmes

The classic blight programme has been based on using single products applied at seven day intervals. In 2007 and again in 2012 this strategy was shown to be highly flawed, and tank mixes of products containing protectant and anti-sporulant products with some kickback applied at less than seven day intervals were needed to control the blight epidemic. Intervals as low as four to five days may be necessary in some instances and, if used, we need to ensure the products we are applying permit these reduced interval applications.


We need to be flexible in our approach to blight control and be prepared to tighten intervals and tank mix products when needed. It is vital too to know the level of disease pressure and where blight inoculum is being found in relation to the potato crops being grown.


There are new ways to get access to this information; we can sign up to various different blight warning services available that send warnings direct to our Smartphone. We can get weather forecasts that not only tell us what the weather is but when we can next go spraying, such as on the Hutchinsons App. We can keep up to date with any reported blight out breaks in our area by logging onto the Potato Council Blight watch service.


On-farm it is vital too that we keep on top of dumps and volunteers, checking for wide rows and poor overlap on field boundaries. Being proactive in all these areas can help in our struggle to control blight.


The main thing is we must not let our guard down and expect that what we’ve done in the past will be the best approach required for blight control in season 2014.


  • Darryl Shailes is root crop technical manager for Hutchinsons, with a nationwide remit. He has been working in potato agronomy for more than 20 years
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