Tough approach needed to beat the problem of potato blight

Apr 30 2008 by Sam Wood, The Journal

NORTH EAST farmers need to take a tough approach to the increasing problem of potato blight, industry experts have said. It is important not just for the sake of efficacy but also for resistance management Dow AgroSciences said yesterday.

Andy Leader, Principal Biologist for the company said: “Potato blight is a devastating disease which has become more aggressive. At this year’s Potato Council Blight Forum, experts reported that over 70% of blight populations tested in 2007 were of the new genotype 13 A2.

“The A2 mating type remained rare in the UK blight populations until 2005 and now it is dominant. With the evolution of genotype 13 it has become apparent that blight is now more aggressive, it can grow faster, it has a shorter latent period and is possibly more active at lower temperatures.

“So effective season-long control of this more aggressive pathogen must be planned with resistance management very much top of mind. The current chemistry available to growers is effective against these new aggressive blight strains, though care needs to be taken in which products to apply when and not over stretching spray intervals.

“With fungicide resistance a significant concern for growers and advisers, measures to minimise the problem should be implemented in any disease control programme.

“General advice is to alternate or block fungicide groups within a programme, to use multi-site products more frequently and to integrate products with more than one active ingredient. To do this effectively growers and advisers need to go into a lot of detail on individual products, their active ingredients, their modes of action, their resistance status and their label recommendations.

“For instance the protectant fungicide Electis will control all known blight races and strains, including A2 isolates.

“It has intrinsically low resistance risk as it contains two complementary active ingredients, mancozeb and zoxium. There is no known potato blight resistance to zoxium, which has a different mode of action distinct from all other potato blight products, or to the multi-site mancozeb which has been around over 40 years.

“There has been no shift in resistance during testing of Electis since launch in 2001 and it has excellent activity against phenylamide resistance strains.

Its label allows up to 10 sprays in any one crop and growers have ultimate flexibility as to how they integrate this fungicide into their programmes.”

Mr Leader said it is also important to apply each blight fungicide at its most appropriate time.