Why are some fungicides not working as well as they did in the past?

Fungicide resistance is an increasing threat to the Irish tillage sector, according to Teagasc’s Steven Kildea.

Due to resistance, he said, some fungicides are not working as well as they did in the past.

“They mightn’t work at all or they may just show a reduction in their efficacy which can then have an effect on the subsequent control and the yield we achieve,” he said.

Speaking at the recent National Tillage Conference, the Teagasc Research Officer said a range of mechanisms contribute to this resistance and they can either be very simple or complex.

“There are three main mechanisms that cause resistance.

“The first is target site mutations and as chemistry has got more and more specific fungicides have targeted very specific enzymes.

“And a very simple change in the DNA of the disease leads to a change in the target site which can make the fungicide less effective or completely ineffective,” he said.

The second reason he cited for the development of resistance was the overexpression of the target site.

This occurs when the pathogen creates more target sites, resulting in an increased amount of chemical being required to hit the individual targets.

And the final cause of fungicide resistance is efflux, he said, which occurs when the pathogen pumps the chemical used to treat the disease out of the cells.

When all three are combined, we have a nasty situation where we are going to lose a lot of efficacy into the future.

Diseases showing signs of fungicide resistance in Ireland

  • Septoria
  • Microdochium spp. (ear blight)
  • Rhynchosporium commune
  • Ramularia colli cygni
  • Net blotch

Is there anything we can do?

Kildea said managing resistance is a balancing act between anti-resistance and control.

There are some basic principles we can apply in terms of managing our crops and how we manage disease control that should be utilised to slow resistance down.

“We need to ensure that if we apply a fungicide it is going to do something,” he said, and if crops don’t need a fungicide, don’t apply it.

“It is important to actually know what we are doing when we are applying these fungicides and if we are applying something it has to provide a benefit,” he said.

He added that fungicides should also be applied in a mixture.

“Applying a mixture is actually of benefit. We need to ensure that we are applying two actives with different modes of action to get the required result,” he said.

“It is important we look at what is in a mixture to see how it will impact on the population,” he said.