Increased levels of resistance to phenylamide fungicides were identified in blight samples tested from the BPC Fight Against Blight campaign last year, compared to 2006. Genetic profiling has also demonstrated that resistance was commonly found in the A2 genotype, which now dominates the blight population in Britain. This highlights that growers may need to update their strategy for Fubol Gold use over the coming season, according to Syngenta Technical Manager, Beth Hall.
Mrs Hall believes the increased level of resistance identified could have been associated with the sustained high blight pressure from early season onwards. "This allowed the blight to go through more life cycles than in a normal year. With resistant strains being generally more aggressive and able to complete their life-cycle faster, we would expect the higher incidence of resistance to be picked up.
"However, all of the results from our blight trials last season indicated that Fubol Gold continued to perform well during rapid canopy growth and it retains an important role as the most systemic blight fungicide to protect new growth from infection," advises Mrs Hall. "But growers must be mindful of the changing blight population, and be prepared to adopt further anti-resistance measures to counter the threat to the phenylamide group", she warns.
For the coming season, Syngenta has temporarily reduced the number of Fubol Gold applications recommended during rapid canopy growth to one. However, the company will continue to work closely with the Fight Against Blight campaign, potato growers and agronomists to capture and test the earliest cases of blight emerging under plastic and on early crops, in order to determine whether the former two-spray recommendation should be reinstated.
Mrs Hall highlights previous work indicates the proportion of phenylamide resistant blight strains declines over winter. "We need to assess the blight population in the early spring this year, to identify the level of resistance remaining in the population and the risk to crops. Until then, growers should proceed with caution and ensure that Fubol Gold is followed with fungicides with an alternative mode of action, taking care not to stretch intervals where the risk of blight is high." She adds that, along with the phenylamide component, mefenoxam, Fubol Gold also contains mancozeb that will control all resistant strains of blight.
Blight strategy
Mrs Hall advocates growers commence their fungicide programme with a Shirlan application at the rosette stage after full emergence. "Shirlan has been shown to be highly effective against all strains of blight. An early application will protect vulnerable growth and add an additional layer of protection on the soil surface to inhibit zoospore activity. We would then advocate a single application of Fubol Gold followed by non-phenylamide fungicides for the rest of the season."
Syngenta Potato Manager, Simon Parker, reports the company is looking at further options and alternative strategies within its existing range of blight fungicides, utilising the very latest new chemistry to provide an effective solution for the coming season, and a robust strategy to counter resistance into the future. "Revus proved to be highly effective under the toughest conditions last year," he adds. "It is set to become the foundation of blight programmes where powerful foliar blight protection is essential."
Ireland finds no A2 blight and low resistance
Billy Cotter of Syngenta Ireland reports that the situation in Eire is very different, with the official Teagasc blight monitoring reporting no A2 strains have been found from 120 isolates examined in 2006 or 2007, with very low levels of phenylamide resistance being identified.
