Herbicide timing critical for black-grass control in rape

UK - November 08, 2007

Correct timing is critical for optimum control of grass weeds in rape crops, warns a leading weed control researcher.

Seven years of Kerb Flo (propyzamide) trials at ADAS Boxworth have shown that optimum grass weed control in rape depends on getting the application timing right. 

“For best results, Kerb Flo needs to be applied when soils have cooled to 8°C,” explains ADAS weed researcher Lynn Tatnell. “Applying the product too early, when soils are still warm could result in propyzamide breaking down faster so reducing the period of control.” 

Getting timing right can be difficult. Growers need to take account of soil conditions and temperatures as well as crop and weed growth. On heavy land, which wets up quickly, growers may have to compromise by applying earlier with a slightly reduced performance. On lighter land, where ground conditions allow a more flexible approach, growers should wait until the soils are cooling. 

“Normally on the heavy land at Boxworth we apply Kerb Flo in the first two weeks of November. This year the soil temperature is 12°C and conditions have been very dry. In addition high dormancy resulted in later germination of black-grass. Therefore, I expect we will be waiting until late November,” explains Lynn Tatnell. 

Where resistant black-grass is present Kerb Flo should be applied at 2.1L/ha in 200L/ha water. Applications to oilseed rape need to be made between 1 October and 31 January. Using Laser (cycloxydim), in tank mix, improves black-grass control even where target site resistance grass weeds are present.