Growers must do more to target grassweed herbicides at the most competitive weeds and maximise the use of cultural and agronomic control methods, ProCam’s technical director, David Ellerton advised.

Recent reports of increasing resistance to Atlantis [mesosulfuron-methyl + iodosulfuron-methyl] (Farmers Weekly, 16 June) had highlighted the dangers of over-relying on a particular product or mode of action, he said.

“Atlantis is a very strong product, but there is such a high proportion of crops being treated with ALS inhibitors now, every time you use them, you’re selecting for resistance.”

Spray timing was crucial and in some cases this spring, ineffectiveness of Atlantis (and other herbicides) may have been down to the product being applied when conditions were too cold, rather than resistance, he continued.

“You need to make sure you’ve got active weed growth, so they take up the chemical.

March and the beginning of April were quite cold and this may explain some of the variable weed control from early treatments.”

Blackgrass resistance would not go away and growers should not rely on sulfonylureas, fops or dims as the only means of weed control next season, he advised.

“Use as wide a range of herbicide groups as possible and, ideally, include a pre-em.

Bigger weeds are more likely to develop resistance.”

There was a range of new chemistry available for next season, including the post-em Axial (pinoxaden) and pre-em Defy (prosulfocarb), he noted.

He also mentioned two new products, yet to be launched, for use in winter oilseed rape and beans – napropamide (Jouster) and dimethanamid (Springbok).

Dr Ellerton said targeting the most competitive grass and broadleaved weeds in each field was also important, along with the use of stale seed-beds, drilling date, density and variety choice.

“Delaying drilling can allow you to miss the peak blackgrass emergence in September and make use of stale seed-beds.

Careful variety choice can help minimise any yield drop from delayed drilling.”

paul.spackman@rbi.co.uk