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Pesticide resistance and the withdrawal of key chemicals could leave growers with just eight ways to combat potato blight, say scientists. Robust blight strategy vital to tackle pesticide resistance

Pesticide resistance and the withdrawal of key chemicals could leave growers with just eight ways to combat potato blight, say scientists.

A robust blight resistance strategy is needed to combat the problem – but success will depend on good planning, alternative modes of action, and the adoption of future technologies, growers have been told.

Managing pesticide resistance in potato crops – including chemistry to target late blight – was explored by Faye Ritchie from ADAS during a recent seminar hosted by the Crop Health and Protection (CHAP) agri-tech innovation centre.

Modes of action

Pesticide resistant blight strains and legislative changes which have seen key chemicals withdrawn mean growers could be left with just eight viable modes of action against the disease, warned Dr Ritchie.

Alternating between these different modes of action within the spray programme – and using approved tank mixes and co-formulated products – offered the most effective approach to help manage resistance development, she added.

But tactics such as adjusting spray timings were less effective.

Dr Ritchie said potato growers were faced with two main challenges when trying to overcome late blight:  fungicide availability and changes in the pathogen population. Both these challenges were linked.

Integrated approach

“Developing a robust strategy for resistance management based on an integrated approach will also help to overcome the issue of fungicide availability – particularly pertinent given the status of mancozeb.

“The first steps should always be to take time to devise a plan ahead of the season, including non-chemical strategies. This should include controlling potential sources of the pathogen, such as outgrade piles.”

Fungicide tank mixes, co-formulated products and alternating modes of action were an effective use of available chemistry. But other measures – such as resistant cultivars – would increasingly allow greater flexibility and help reduce dose rates.