Resistance to new blight strain a concern

There are lessons Irish potato growers can learn from farmers’ experiences in dealing with the new EU43 strain of blight in other countries, the national potato conference’s attendees heard last week.

The strain is just a few years old but has already developed a resistance to two of the remaining chemistry tools farmers have in the fight against late blight – Revus and Zorvec – with the strain detected in Oak Park last year.

Senior crops specialist with SEGES Innovation in Denmark, Lars Bodker, highlighted the need to mix at least two modes of action, alternate these modes of action as much as possible and to deploy decision support systems in spraying plans to combat the strain.

Farmers in Denmark were left with their “backs against the wall” when Zorvec resistance was found in EU43 in 2023, but agronomists there have developed a spray regime to help protect crops.

This strategy has seen the fungicide treatment index – the number of full-rate fungicide treatments going out on crops over a single growing season – increase.

“One of my primary focuses when I started my career was to reduce fungicide inputs in potatoes.

“But what happened really is that in my time, we have increased the treatment frequency index by one spray each year since,” Bodker said.

“Now, we are up in total when you add two full doses in each spray in a 12- or 13-spray plan, you are on a treatment frequency index of 25,” Bodker added.

“That is not a sustainable way of controlling late blight into the future.”

The conference heard that resistance genes should be mixed with modes of action to help prevent EU43 from evolving resistance to these genes.