Using varietal resistance to control blight in potatoes

The conversation about Blight in Potatoes and current farm practice

Late blight (Phytophthora infestans) is a devastating disease found in potato crops – you go back in history to revisit the Ireland potato famine to understand what could happen if late blight in potatoes is not controlled properly.

In modern times we have adapted to several techniques – the most popular and effective way is to spray the crop every 7 – 10 days during the main growing season.  

Obviously, the reality here is that if you were looking at this from an environmental aspect this doesn’t look so good – but on the flip side what other alternatives do we have in the armoury?

There is also the continuing issue of newer strains of the blight pathogen evolving.  Add to this, the fact that our growers are facing a new threat in the form of continuing withdrawal of the basic but none the less very effective key chemical actives used in blight control (e.g., mancozeb).  The consequences growers are now facing because of this adds further pressure to the current chemical control cabinet. Making it difficult to build good application strategies which reduce the risk of fungicide resistance developing.

Early versus late blight

Alternaria, also known as early blight, is a mainly soil-borne fungal pathogen that affects potato crops. Symptoms usually appear a few weeks after emergence and start as very small black or brown spots on lower leaves which then coalesce.  There are two types of Alternaria with predominant species is Alternaria solani. The other species Alternaria alternata tends to infect later in the season.   Late Blight has three dominant strains, 6_A1, 36_A2 and 37_A2. 

However, genotypes or 'strains' of blight evolve over time and require constant monitoring.  It is important to be aware that strains can develop resistance to recognised fungicides, although a robust spray programme using multisite actives and alternating different modes of action will really reduce this risk.

So, what can we do?

Varietal resistance

Seed breeders and producers consider varietal resistance as the key factor in the toolbox in a world of reduced armoury against debilitating plant diseases such as early and late Blight in potato crops.

AHDB has developed a digital tool to help growers select alternative potato varieties. The Potato Variety Comparison Tool combines AHDB data on varieties planted in Great Britain and information on disease resistance from the (national) Potato Variety Database run by SASA. Growers will be able to use the tool to compare the variety they usually grow with alternatives that have improved disease resistance ratings.

Forthcoming research

AHDB are currently working on a variety of projects and initiatives based around alternative controls of early and late blight in potatoes including spore trapping, and nutrition-based research linking storage practices.

8 achievable take - home points: -

  • Rotation length
  • Use varietal resistance
  • Hygiene - manage out grade piles, groundkeepers
  • Use clean seed
  • Hutton Criteria
  • Monitor your crops regularly and use in conjunction with decision support systems such as Blight watch, Fight Against Blight
  • Prioritise the use of biological, cultural and chemical controls
  • Know your strains

You can find  further information on this topic on the following links:

Blightwatch Fight against blight The Fungicide Resistance Action Group (FRAG-UK) Potato Disease Identification Potato Variety Comparison Tool

Antonia Walker

Senior Knowledge Transfer Manager - Potatoes