Chemical controls can be broadly split into four groups: pre-emergence and post-emergence herbicides, non-selective control across whole fields (i.e. pre-drilling glyphosate), and patch spraying.
In-depth advice
1. Pre-emergence
Pre-emergence herbicides such as Liberator (flufenacet + diflufenican) remain the backbone of chemical black-grass control and, when paired with a solid programme of cultural controls, can prevent black-grass from stealing yield.
Pre-ems are applied immediately after drilling and taken up by weeds either through roots absorbing the active ingredient from the layer containing the herbicide, or by shoots emerging through this treated layer. Application conditions can therefore greatly affect efficacy.
Flufenacet remains a highly effective active ingredient for pre-emergence black-grass control, and when used in Liberator in conjunction with Proclus (aclonifen) typically achieves high levels of control. The addition of aclonifen can increase control by 10-15%.
Stacks or sequences of other actives, such as pendimethalin, prosulfocarb and tri-allate are also possible to improve control.
Post-emergence
Post-emergence herbicides are a vital part of integrated black-grass control programmes, especially where pre-em control has been compromised (e.g. due to weather) or weed emergence is protracted.
Contact post-emergence herbicides like Atlantis OD (mesosulfuron + iodosulfuron) and Monolith (mesosulfuron-methyl + propoxycarbazone) work by being absorbed through weed leaves. Hamlet (mesosulfuron, iodosulfuron + diflufenican) is also primarily contact-acting, but has some residual activity.
Ideally, growers should apply a post-emergence spray while black-grass is still small and easier to control.
3. Non-selective (whole fields)
Non-selective herbicides, principally glyphosate, have been a cornerstone of black-grass control for many years.
Targeted use of glyphosate can significantly reduce the pressure on other in-crop chemistry, minimise the need for intensive cultivations and achieve big reductions in weed populations.
Spraying off weed flushes before autumn or spring drilling means less black-grass emerges within the crop, which would otherwise need controlling with pre- or post-emergence products.
However, over-reliance on glyphosate must be avoided and best practice followed to protect the efficacy of this important tool.
4. Patch spraying
Where black-grass has emerged late or survived other chemical and cultural controls, the option of last resort where hand rogueing is not feasible may be to spray-off affected areas of crop with a non-selective herbicide, such as glyphosate.
Doing so before black-grass sets seed in late June into July is essential to prevent potentially high levels of seed return in following crops.
Mapping black-grass helps identify areas requiring patch spraying and best practice guidelines must be followed when using glyphosate in this way.
