Fungicide guidance remains unchanged for potato growers

Tuesday, 4 August 2020

Results from blight fungicide testing show no significant decline in sensitivity according to research supported by AHDB.

The data taken from trials carried out throughout 2019 means no changes in recommendations for blight control issued by the Fungicide Resistance Action Group (FRAG). There were however some differences in control among some of the actives tested, these were at doses well below field rate.

Researchers from the James Hutton Institute tested 15 isolates representing three different genotypes of the blight pathogen, including newer types 36_A2 and 37_A2 and older 6_A1. They tested a range of doses of seven different fungicides for their efficacy in reducing lesions on potato leaves. Their aim was to ascertain the EC50 - the dose at which the fungicide reduces lesion growth by 50% compared to the untreated control group.

The majority of the data from last years’ trials was consistent with results from 2018. This meant no meaningful changes in the EC50 for the fungicides tested. Despite this, there was some variation between isolates with slight reductions in efficacy of certain fungicides against the newer genotypes.

This included fluopicolide, where efficacy was slightly lower against 36_A2 than other genotypes and mandipropamid, which required slightly higher doses against 37_A2 compared with 36_A2 and 6_A1.

Included in the testing for the first time this year was amisulbrom to which a slightly lower efficacy against 36_A2 than both 37_A2 and 6_A1 was noted. Also included for the first time was oxathiopiprolin which proved effective at very low doses with EC50 values in line with other studies.

Research leader David Cooke said: “While there are indications of minor genotype-specific differences in efficacy, this data does not show any immediate cause for concern for potato growers that newer blight genotypes are causing problems for fungicide programmes – especially in this season that has been generally ‘low risk’.

“This doesn’t mean there’s room for complacency however. Growers are advised to follow FRAG guidance and adopt Integrated Pest Management (IPM) approaches where possible.”

All the variations between isolates were found at well below the dose rates used in the field and, as such, were not considered significant enough to require changes to FRAG guidance. 

Best practice for controlling blight using fungicides remains making full use of fungicides with different modes of action.

You can do this by:

  • Avoiding relying on a single fungicide group
  • Targeting specific products to appropriate growth stages
  • Using multi-site fungicides such as mancozeb
  • Checking product labels for manufacturers’ recommendations on dose, timing and spray intervals, and restrictions

Growers and advisors can support this research by joining the blight scout initiative to get a sample pack and sending blight samples to the Fight Against Blight service.

For more information on controlling blight in potatoes please visit our blight page on the AHDB website.

Comparison of sensitivity to a range of fungicides in contemporary genotypes of Phytophthora infestans in 2019

Read the full report