Growers are being warned to continue to actively use integrated weed management programmes after Bayer grassweed resistance testing has confirmed reduced sensitivity to key active ingredient flufenacet.
The testing has found, in a few isolated cases, black-grass from farms in Germany with reduced sensitivity to flufenacet. More troublingly, results show that rye-grass with enhanced metabolism resistance to flufenacet is present on a small number of UK farms, says Bayer.
There are no results indicating flufenacet resistance in black-grass in the UK or overseas, but reduced sensitivity in Germany should act as a wake-up call to farmers, it says.
In practical terms, Bayer does not anticipate these results leading to a radical change in black-grass management. But product stewardship continues to be of crucial importance, says Bayer’s Dr Gordon Anderson-Taylor.
“No active is safe from the risk of resistance, so it is always important to vary modes of action throughout the herbicide programme to slow down the development of any resistance. Achieving the best possible results with herbicides is also important, using pre-emergence herbicides like Liberator at the true pre-em timing will get more consistent results.”
The situation with rye-grass is more concerning. In the study, some UK populations required more than 300g/ha flufenacet applied pre-em for 50 per cent rye-grass control and more than 3kg/ha flufenacet for 90 per cent control. These figures are well above the label rate for flufenacet which is 240g/ha, hence the resistant classification for these rye-grass strains. Researchers also found rye-grass samples from France and the USA with resistance.
“The results are worrying for farmers with rye-grass problems, but I would like to emphasise that resistance is unlikely to be widespread,” says Dr Anderson-Taylor. “Once again, the research is focusing on the most resistant samples available.
“Understanding the rye-grass population on your farm is essential. A resistance test can tell you the status of rye-grass and help you manage it more effectively. But there are three things all farmers dealing with rye-grass need to do to mitigate the risk: cultural controls, crop rotation and varying herbicide modes of action.”