The Bayer/ NIAB survey tested 197 Italian ryegrass samples for resistance to flufenacet. Trials also looked at cross-resistance to other common pre-em actives and how a farm standard pre-em programme would perform against the hardest to control populations.
73% of samples tested were still susceptible to flufenacet. But 17% showed reduced sensitivity and 10% were not controlled by field rates of flufenacet as a single active.
Looking across the whole survey, there is variable herbicide sensitivity; around the country and even between fields on the same farm. This means that farmers need to be prepared to resistance test and plan control programmes on a field-by-field basis.
22 samples were selected for cross-resistance testing to other pre-em actives. It showed a correlation between flufenacet, prosulfocarb and pendimethalin resistance. But we need to be careful with how we interpret this according to Mr Cussans. “If there is resistance to one active, it doesn’t automatically follow that you have resistance to the others.”
Importantly for many farmers, there is no resistance to glyphosate in ryegrass in the UK, unlike Australia for example. So, they still have one of the most effective out of crop controls available.
Firstly, use the full range of cultural controls to manage populations before the herbicide programme. Then the aim should be to employ different modes of action within and between seasons to prevent strong selection pressure on one or two actives.
Researchers tested 7 of the most resistant ryegrass samples to see how combing modes of action stabilises control in the field. “Combining three actives, in this case Liberator + Proclus largely but not completely ‘overcomes’ flufenacet resistance.”
Farmers and agronomists sent in nearly 200 ryegrass samples for the NIAB / Bayer ryegrass 2021 ryegrass survey.
As part of this season’s CropCheck initiative, our technical managers have partnered with local farmers to track disease progression in commercial wheat fields across the UK and Ireland.