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Talking Roots with Darryl Shailes: Dealing with blight

The blight pressure had reduced considerably since July to the extent that the Blight Demo trials organised every year in Derbyshire have had to be cancelled as the infection levels are too low for clear observable differences between products and programmes. 

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It is because the trials are always planted later than normal field crops and there has been very little disease pressure over the last month or so. Also our own trials near Holbeach in Lincolnshire are struggling to take shape.


Prior to this week, the last blight alert I received was on July 12 and my Dacom system has been showing very few red warnings, with just the odd blip, so pressure has been low and growers have been able to be less vigilant with their blight programmes.


That was until now, the first week of September as I’ve just had two consecutive Smith Period warnings come through on my phone and the Dacom system is showing bright red for the whole week, so blight pressure as we finish off the growing season is once again high.


This means most crops, especially those destined for storage will need to have something for tuber blight included at the desiccation timing to ensure no blight is carried in to store. In these high risk crops a blight programme needs to be continued right until all the haulm is dead.


Crops are senescing earlier than normal with only the most indeterminate crops on the best soils still going strongly.


Early senescence can lead to Black Dot issues so growers should be vigilant and field assessments done to crops at risk. Where problems are found priority should be given to lift as soon as the skins are set as it tends to get worse the longer the tubers are left in the ground.


Bruising can also be an issue where crops senesce early, that and dry soils at burn down can make the situation worse in many varieties.


If you can, monitor soil moisture deficient right through to burn down and do not let them get over-dry as once a crop start to bruise at lifting its very difficult to manage.


Another issue for storage is the amount of blackleg in many crops again this season. Blackleg as we all know can lead to bacterial breakdown in store so it very important to ensure crops with any level of black leg have the skins well set before lifting commences to reduce the spread.


Glufosinate is now gone from our armoury at desiccation except where haulm is managed by a flail and spray technique. Glufosinate was especially useful where grass-weeds were an issue and in dry soils. The other actives available for haulm desiccation have very little effect on the clumps of meadow-grass which can be a problem at lifting especially where crops have died off early.


Most crops will now need sequences of diquat and carfentrazone.


Last year there was the odd incident of internal browning when using diquat in very dry soils, something I hadn’t seen before, so a SMART test is essential to determine the rate of Diquat which can safely be used in the programme. Recent work has shown using a

higher water volume with slower forward speed than normal at the first application timing of diquat can help on getting effective haulm control.


Lastly, when planning for next season, remember current best practice for PCN sampling is hectare block’s with 50 cores per sample.

  • 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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