Resistance to wild oat herbicide prominent in the south east

Herbicide resistance in grass weeds is one of the challenges facing the tillage sector at present. Ronan Byrne, a PhD student at Teagasc Oak Park, told the Teagasc National Tillage Conference what levels of resistance are like in wild oats on farms.

Wild oats have been found to have resistance to products like Axial (pinoxaden), Falcon (propaquizafop), Foxtrot (fenoxaprop) and Stratos Ultra (cycloxydim).

A survey of samples, from fields where resistance was expected, found a significant resistant population to these herbicides in Co. Wexford.

“What we found in this survey was that there were a number of populations of wild oats in Co. Wexford that were actually resistant to these herbicides,” Ronan explained.

This population in Co. Wexford was randomly sampled in 2017 and a subset of the population was tested for resistance to pinoxaden and fenoxaprop.

Around 55% of the populations were resistant to at least one of these herbicide active ingredients.

“Of this 55%, 8% of the total samples were resistant to Axial and all of the Axial resistant populations were resistant to Foxtrot to varying degrees.”

The main mechanisms for resistance:
  • Target site resistance – a simple mutation can stop the herbicide from binding to its target within the plant;
  • Non-target site resistance – the ability of the plant to metabolise herbicide active ingredients.

Ronan added that glasshouse studies have shown that some populations carry both types of resistance.

What causes resistance at farm level?
  • The misuse of herbicides – using the same herbicide year-after-year;
  • Lack of crop rotation;
  • Using reduced rates of herbicide – associated with non-target site resistance;
  • Lack of an integrated weed management approach.