By Ken Fletcher

BLIGHT HAS been a particular problem throughout the UK this year and has needed constant vigilance to keep on top of it, but as the saying goes, 'it's the old dog for the hard road' in terms of control methods.

Dr David Cooke, of the James Hutton Institute, said that two blight strains, 6_A1 and 13_A2, dominate late blight populations in the UK and have done so since 2005. In 2014 the former accounted for 60% of the total blight population and the latter, 28%.

These dominant blight strains are more aggressive, having a shorter three or four-day life cycles and producing more spores per leaf area (30-40,000 spores per square cm of lesion).

Therefore, stronger fungicides with good, proven anti-sporulant activity and longevity of action are needed to control this disease. Paul Goddard, of BASF, argued that Invader at its label rate of 2.4 kg/ha is one of the most complete blight fungicide you can get.

“I am the first to admit that Invader is not be the newest blight fungicide. But just because something is new and shiny does not make it better than the establish ‘old guard’," he said.

"Invader has consistently outperformed products such as Revus or Infinito in our Eurofins trials since 2012. But don’t just take my word for it.

"At BASF we have started two fascinating new projects with the help of Ruairidh Bain, at SRUC. The first will look into the anti-sporulant activity of blight fungicides. The second aims to assess the boost Invader gives to the following treatment in a programme.”

The trial testing anti-sporulant activity is entitled testing sporangia viability following fungicide treatments. “It combines field and laboratory work to measure the impact on sporangia production but goes further by also looking at spore viability per se," he said.

"With current blight strains producing significantly more spores than just a few years ago, a product with anti-sporulant activity is a key tool in managing blight risk. However, it is more than antisporulant activity that is important.

"Products that also reduce the viability of any spores that do get through, as we believe Invader does, have a two-pronged attack against the disease and may in part explain why Invader is such a strong product against modern blight. Anti-sporulant activity is a great place to start, but that is only part of the story,” he pointed out.

The trial will use field applications across replicated plots. Samples of foliage will be inoculated with blight and after lesions have appeared, sporulation will be encouraged in the laboratory under controlled conditions.

Any spores that develop will be harvested and the viability of sporangia in relation to the actual fungicide assessed on clean leaves of three potato varieties with different levels of susceptibility. This will confirm, or otherwise, that Invader has strong anti-sporulant activity and goes on to reduce the viability of any spores produced in the field.

“This characteristic has been observed in the field with Invader but now we are looking to have scientific data to prove this," added Mr Goddard.

The second trial looks at blight control from a totally new angle and aims to quantify the boost to the curative activity Invader (and other BASF fungicides including coded products) gives to the following product.