UK researchers confirm fungicide resistance in oilseed pathogen
For the most part, winter oilseed rape crops sown out during the month of August have emerged with vigour.
This is according to Teagasc tillage specialist: Shay Phelan.
He further explained: “Sorting out grass weeds and volunteer cereals is the key management priority for growers right now, where winter oilseed crops are concerned.
“Spraying crops with a fungicide to prevent the onset of phoma is another important requirement at this stage.
“However, choice of product is important in this regard. Some chemistries will also have a growth regulation impact.
“Growers may not want this to be the case as they will want individual plants to be large enough to fend off the impact of pigeon grazing later in the season.”
Meanwhile, scientists have identified resistance to a major group of fungicides in populations of the oilseed rape pathogen Plenodomus biglobosus for the first time worldwide.
The discovery raises concerns that control of phoma - one of the most serious diseases of oilseed rape - could become increasingly challenging.
Phoma can cause substantial yield losses in oilseed rape and is caused by two related fungal pathogens: Plenodomus lingam and P. biglobosus.
P. biglobosus trials
While P. lingam has historically received greater attention, P. biglobosus has become increasingly important in UK and European crops.
Scientists from Rothamsted Research in the UK screened populations of P. biglobosus collected from the UK and Poland.
They found that 95% of UK isolates were resistant to the SDHI (succinate dehydrogenase inhibitor) fungicides boscalid and fluxapyroxad, compared with just 6% of Polish isolates.
Some UK isolates showed up to a 500‑fold drop in how well fungicides work against them under laboratory conditions.
The researchers also confirmed that resistance was linked to mutations in genes encoding the fungal succinate dehydrogenase (SDH) enzyme, the target of SDHI fungicides.
The study also found little evidence that these mutations reduce the pathogen's fitness, suggesting resistant strains may persist in field populations.
Rothamsted's Dr Kevin King, who led the research, said: "The scale of resistance we detected in UK populations was striking.
"This is the first confirmed report of SDHI resistance in P. biglobosus anywhere in the world."
Further research is now needed to determine what impact this may have on phoma disease control under field conditions.
The findings follow recent Rothamsted reports of reduced sensitivity to azole fungicides in European populations of both phoma causing pathogens.
It also highlights the growing importance of resistance monitoring and integrated disease management strategies.
