UK potato growers warned of the threat of shifting blight pressures

Speaking at a recent ‘Potato Thought Leadership’ event sponsored by Adama in the UK, Dr Huub Schepers, plant pathologist at Wageningen University and Research Centre in the Netherlands, warned potato growers and agronomists about the shifting disease pressures which he believes will make the fight against blight an increasingly difficult battle to win.

Adama’s ‘thought leadership’ programme is designed to forge closer links and greater understanding with industry experts and stakeholders from across the combinable and root crop sectors. Speaking at the company’s first of such events for potatoes, Dr Schepers explained to a contingent of growers, agronomists and processors that whilst blight in UK crops has historically been caused by Phytophthora infection, there are in fact three main pathogenic species across Europe: Phytophthora infestans (late blight), Alternaria solani and Alternaria alternata (early blight), with all three species capable of causing significant crop damage and losses as a result of tuber and/or leaf infections.

In order to effectively combat all three species, Dr Schepers recommends a four-point plan:

1. Where possible, look to protect crops by extending the rotation;
2. Choose a variety with good blight resistance;
3. Remove volunteers to eliminate blight hosts and sources of infection;
4. Select a fungicide which offers the appropriate level of efficacy, longevity and resistance to the prevalent disease pressures.

With the latter in mind, Dr Schepers warned of the dangers posed by increasing resistance to some fungicidal active ingredients, highlighting that a number of fungicide resistant Alternaria isolates have already been identified in Europe. He also highlighted that climate change posed a significant threat, with warmer, wetter growing seasons creating favourable conditions, particularly for Alternaria. He also warned that whilst many crop protection treatments offer preventative security, few current treatments deliver a curative action against blight. Without proper early season protection, and until 100% resistant genetically modified varieties are commercially available, infected crops will continue to be susceptible to significant losses.

Early season protection is vital

Dr Schepers warns that protection during the early growing season is critical to ensuring that crops remain clean: each day, new, unprotected leaves emerge and present a fresh target site for blight infection to take hold. Re-infection of these leaves will be exacerbated by wet weather conditions, with rain splash rapidly causing infections to spread.

When weather conditions are critical for infection, and spores are present in the rapid canopy development phase, it might be necessary to shorten the spray interval: under exceptional conditions this interval might need to be as close as every three days, especially when aggressive strains of Phytophthora are present. Dr Schepers also advises growers to adopt a field-by-field protection policy, warning that meteorological patterns and strain pressures can vary significantly across a relatively small distance.

For future crop protection strategies to be truly effective, Dr Schepers emphasises the need for new active ingredients, which can specifically target the most aggressive strains of infection, to be developed. Genotype testing of isolates will be required so that the most appropriate active ingredient can be selected on a site-by-site basis.   In the meantime, growers and agronomists must make certain that the current range of available fungicides is used in the correct manner in order to prevent resistance from building and to maintain an acceptable level of control.

Up to date news and disease pressure alerts, as well as the latest thoughts regarding disease control best practive can be found on the EuroBlight website (www.euroblight.net).