Timing especially critical for resistant black-grass control in rape this autumn

UK - October 08, 2007

Protracted dormancy and germination of black-grass this season means correct timing of post-emergent oilseed rape weedkillers will be critical to control resistant black-grass warns a leading grass weed expert. 

“The right timing for herbicide applications in oilseed rape this autumn will be critical for optimum control of black-grass,” warns James Clarke of ADAS. “For best results herbicide properties need to be matched with likely emergence patterns of weeds and soil conditions.” 

Use of Kerb Flo (propyzamide), applied in oilseed rape, is an important tool for controlling resistant black-grass, but best results occur when used on cool and moist soils once black-grass seeds have germinated.  

“Our work over several years at ADAS Boxworth showed that best application timings of propyzamide were after soils had wetted up.  The combination of residual activity and good control of plants with shallow roots means applying in November typically gave the best results.  Applications at the full dose gave the most reliable control of resistant black-grass.  Where roots of the black-grass were deeper a contact graminicide needed to be added to maintain level of control,” advises James Clarke. 

Kerb Flo can be applied between 1st Oct to 31st Jan when soils are moist and cool. As optimum timing varies from year to year, Dow AgroSciences issues regular bulletins to agronomists on optimum timing. Where resistant black-grass is a threat Kerb Flo should be applied at 2.1 L/ha; in other circumstances otherwise 1.75 L/ha can be used.