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Talking Roots with Darryl Shailes: The question of blight


When I last wrote in early May it was raining outside, 14degC and the question was whether we would have a bad blight epidemic in 2014. The signs were already there.

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We’d had a very mild winter, downy mildew was already being recorded in other crops, months earlier than normal, volunteer potatoes were emerging everywhere and the potential risk was high.


As I’m writing in mid-July, my phone has binged twice in the last three days to say Smith Periods had just been recorded in all of my registered postcodes with Fight Against Blight/Blight Watch; my Dacom Forecast Extra is showing red for blight and alternaria and the

blight epidemic of 2014 is in full swing.


The first confirmed blight outbreak was recorded on May 7, and now when I look at the Potato Council websites’ blight map there have been well over 75 confirmed outbreaks across all the major potato growing areas of the country. This is just those recorded by Blight

Scouts as part of the Fight Against Blight (FAB) campaign, in reality this is the tip of the iceberg.


In the worst cases whole fields have already been burned off and others have had various foci burned out with diquat.


Spray intervals are down to three to four days on some fields with complex and expensive tank mixes and still the blight is not completely under control. However other fields have very little blight, if it can be found at all and intervals are at their normal seven days even if the programme is more robust than normal.


In addition to late blight being prevalent in many crops, alternaria is also showing its head in many fields and causing the most badly affected crops to show signs of early senescence that may result in some of them not making their required market size, specification and yields being reduced.

So what’s happened and what can we learn?

Certainly in some situations programmes haven’t been tight enough early on. The lack of full Smith Periods early gave many a false sense of security but as we discussed in May the new strains of blight such as Pink 6 and Blue 13 are more aggressive than those in the 1970s. These new blight strains don’t need the strict climatic definitions of a Smith Period to become active and are able to infect crops over a wider range of environmental conditions. Do we as an industry need to seriously question what models we follow in the 2015 season?


Also where programmes were started early, in many situations the products chosen were not robust enough and the intervals too wide to achieve good control with crops growing very rapidly and the infection pressure being much higher than normal at the start of the season. We don’t have any truly systemic and curative products available which control all the strains of blight out there so intervals during rapid canopy should have been reduced to five days or so with robust products from the outset where the blight pressure was very high.


Many of my colleagues reported active blight in dumps across the country which were not being controlled effectively despite all the industry warnings every year.


On top of this we have also had high alternaria pressure which had been missed under all the attention being paid to blight and as most of the more robust phytophthora actives do not have any alternaria activity it’s slipped in under the radar.


It is probably too late to dramatically alter what is happening this season apart from ensuring good tuber blight actives in conjunction with anti-sporulants are used right to the end of the programme until all the green material has gone, but mainly to learn the lessons from 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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