Sarah advises on post emergence herbicides
21 Nov 2017
A single pre- or post-emergence herbicide is rarely sufficient to control grass weeds such as sterile brome and black-grass. Good control of grass weeds comes from applying a robust pre-emergence herbicide and following this with a peri or early post emergence treatment whilst weeds are still small. If treatment is delayed weeds become bigger and herbicides less effective, particularly if populations have high levels of herbicide resistance. Weeds also need to be actively growing for the herbicides to have the greatest effect.
A range of herbicides can be applied at the peri or post emergence timing including flufenacet, picolinafen, prosulfocarb, pendimethalin and, diflufenican. Flufenacet is integral to any black-grass control programme but over reliance on any one active is undesirable as it can lead to resistance. True post emergence herbicides that contain mesosulfuron and iodosulfuron are ALS inhibitors and many black-grass populations are already resistant to these herbicides, again small targets and active growth are key to maximising control.
Timings and rates are dependent on crop and weed growth stage and calendar date so check labels before application.