OILSEED RAPE herbicides used to control blackgrass provide a good opportunity to slow resistance development and control resistant weeds already present, experts have advised.

“It is important growers use the opportunity that oilseed rape offers,” said Rothamsted Research’s Stephen Moss. Target site and enhanced metabolism resistant blackgrass strains are widespread across England, so correct product choice is vital, he said.

In trials at ADAS Boxworth, Kerb Flo (propyzamide) killed around 99% of blackgrass in oilseed rape established by minimum or no tillage – even where weed populations were high and target site resistance to key cereal weed killers was present.

“Kerb is good on min-till or broadcast crops where the soil has not been disturbed and the [blackgrass] seed is nearer the surface,” said ADAS’s Lyn Tatnell.

“It is less effective in plough-based systems.” Where ploughing was used, 85% of blackgrass was controlled, results showed.

Kerb Flo has a different mode of action to herbicides associated with target site resistance, such as the ‘fops’ and ‘dims’, so it can help manage difficult blackgrass situations, added Dow AgroSciences’ Colin Bowers.

But even though there is no known resistance to Kerb, making it a good option for break crops, growers should not become over-reliant on it, noted Mrs Tatnell.

Dow AgroSciences recommends applying Kerb Flo after the oilseed rape crop has three true leaves, from 1 October to 31 January, at 2.1 litres/ha.

For more on autumn herbicides, see this week’s FARMERS WEEKLY magazine (23 September 2005).