‘Zero tolerance’ stance with blight

Potato blight seems to be getting harder to control.

So growers must be prepared to maintain a “zero tolerance” approach to the disease, urges the BPC.

“Scientifically it is not easy to prove that blight is becoming more aggressive,” says agronomist Mark Prentice.

“But there are certainly anecdotal accounts that the pathogen is getting more difficult to control.

“So growers really must be on the ball this season.

The key is to get on top from the start, because once blight gets into crops it can be hard to stop.”

Analysis of positive samples of the disease from 350 volunteer “scouts” last year found that 38% of them were of the A2 mating types of the fungus.

Those results indicate that the proportion of A2 strains in the population has risen from the 9-10% measured 10 years ago, notes Mr Prentice.

That, in theory, means there is a greater chance of them recombining with the common A1 populations to create more diversity and potentially more aggressive strains, he explains.

“But so far no zoospores have been found, which would have indicated that the two strains had successfully mated.

“As a result a whole new blight research project has been commissioned by the BPC this year.

It will involve a co-ordinated national programme over three years, led by SCRI looking at population diversity, mating types and zoospore survival to see whether control strategies need to be altered.”

The encouraging news is that despite the findings all modern fungicides offer control provided they are applied correctly.

This season the arrival of two products containing new active ingredients and approval for an increased rate of another well-established one is particularly welcome, he adds.

New are Valbon (benthiavalicarb-isopropyl) from Certis and Bayer CropScience’s Infinito (fluopicolide + propamocarb), while Syngenta has introduced a new higher rate 0.4 litres/ha rate of Shirlan (fluazinam).

It is important to have a range of effective molecules available in the armoury to counter the threat of more aggressive strains and possible resistance, Mr Prentice explains.

“One of the key weapons farmers must have in controlling blight is the ability to change products regularly.”

But the first line of defence is to eliminate sources of the disease by planting healthy seed and tackling the previous season’s legacy, he stresses.


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