Blight Strategy - Potato blight control 2015

While the winter was relatively mild, cold spring temperatures have meant late planting and slow growth, meaning potato crops in most areas are significantly behind for the time of year. With the start of June and temperatures showing a rise, blight once again poses a threat as conditions become suitable for its sporulation and spread. This article provides an update on field control for the coming season to help plan protection of crops.

Waste potato dump management

Dumps are an important source of blight and other disease, so good hygiene is crucial.  To prevent re-growth, cover dumps with black plastic to promote rotting.  Check dumps regularly to ensure that the covering remains intact.  Any growth should be sprayed off with glyphosate or diquat (Reglone) and covered.  Reglone use on potato dumps is subject to an Extension of Authorisation for Minor Use (EAMU) in the UK, so before using it, you must be in possession of, and have read, the full EAMU (20111882) 

It should be noted that this EAMU expires on 31st December 2015, so no applications of Reglone should be made to potato dumps after this date.

Fungicide timing and coverage are critical.  No matter how good the product, nothing makes up for a late start, stretched intervals or areas left unprotected.  Once blight has got a foot-hold in the crop, it’s almost impossible to eradicate it.  Angled nozzles with a medium spray quality give better canopy cover at all stages of growth.

Start protecting your crop from blight whenever the first blight warning is issued or when plants meet within drills (whichever is earlier).

Blight warnings are issued by AFBI and CAFRE throughout the season in the farming press and via DARD Blight-Net Text Alerts.  Blight-Net will be active from early June and further information can be accessed from the DARD website www.dardni.gov.uk (follow the link from ‘Farming and Countryside’ and then ‘Potatoes’).  If you would like to register for Text Alerts, contact Iain Johnston, CAFRE Crops Adviser, on 02837529084 to register your number.

Blight genotypes – a changing picture

Rapid changes in P. infestans populations causing late blight in Europe, America and Asia, including the emergence of strains which are more aggressive or have reduced fungicide sensitivity have been observed: the Northern Ireland population is no exception.  AFBI researchers are part of an all-Ireland project MonPESC (Monitoring Pathogen Evolution for Sustainable Cropping) which focuses on key crop diseases including blight, this allows the population to be monitored and invasive genotypes characterised to allow integrated blight control strategies to be deployed.

AFBI monitoring of samples provided by DARD Potato Inspectors and CAFRE Crops Advisers highlights the differences between blight populations in Northern Ireland and mainland GB and the need to update and maintain robust control programmes to counter the shifting blight strains.

While the dominant genotypes were still the older A1 types, which seem well-suited to conditions here, monitoring showed that in 2014, the aggressive A2 mating type, Blue 13 genotype, which is resistant to phenylamide fungicides, was found in eight Northern Ireland crops, up from one instance in 2013. Blue 13 was the dominant genotype in GB and several mainland European countries including France, Belgium and the Netherlands.  The other frequently found genotype in Great Britain, known as Pink 6, has been very rare in Ireland, but rose from one instance in NI in 2013 to seven in 2014, most likely due to the warmer weather which it favours.

Through the EuroBlight network, we maintain contact with scientists working on late blight throughout Europe and will update Northern Ireland growers as necessary.

2015 control programmes

It is good practice to use a range of fungicides with different modes of action and not to rely on any one active ingredient for more than half of the programme.  This makes best use of their different types of activity and reduces the risk of selecting for blight strains resistant to any one fungicide.

Options for early season use during rapid growth are Consento and other formulations containing the only non-phenylamide systemic, propamocarb, or the translaminar mandipropamid (in Revus), which is best used as a tank-mix with Shirlan (fluazinam).  These have performed well in controlling foliage infection early season in AFBI trials, as has ametoctradin + dimethomorph (Resplend), which was introduced in 2011.  In 2014, the proportion of phenylamide-resistant blight strains increased significantly therefore growers should limit applications of products containing phenylamides (e.g. Epok, Fubol Gold), to a maximum of twice in the programme.

Continue the programme with a translaminar (e.g. Curzate, Infinito, Invader, Revus) or protectant (e.g. Dithane NT, Electis, Ranman, Shirlan).  Note that both Revus and Invader contain ingredients which have the same mode of action (CAA fungicides); to reduce the risk of resistance, no more than 3 consecutive applications of these products may be applied and the total number of applications is also restricted to no more than half of the intended spray programme (for further advice see product labels and consult (www.pesticides.gov.uk).

The programme should be completed with at least three sprays of a product with tuber blight activity (e.g. Infinito, Ranman, Shirlan).  It is vital that the crop is protected until the haulm is dead: blight can attack green leaves when the crop is senescing or even after a desiccant has been applied and this can lead to tuber infection.  To reduce the risk, a fungicide should be applied with the desiccant (check product labels for approved tank-mixes) and if necessary further fungicide applications made until the haulm is dead.

Remember to check your buyer’s protocols for a list of approved chemicals.

If you have any queries, please contact your local Crops Development Adviser:

• Londonderry/Antrim: Gerard McDaid 028 77721821
• Tyrone, Fermanagh, Armagh: Iain Johnston 028 3752 9084
• Down: Aveen McMullan 028 4461 8075.

Notes to editors: 

AFBI carries out high quality technology research and development, statutory, analytical, and diagnostic testing functions for DARD and other Government departments, public bodies and commercial companies.

AFBI's Vision is “Scientific excellence in Northern Ireland …  serving the world”.

All media enquiries to AFBI Press Office

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