Black-grass management: stacking not just about mixing herbicides

Winter wheat growers facing problems with black-grass shouldn’t just think that ‘stacking’ is all about tank-mixing different herbicides together.

Instead, it should encompass ‘stacking together’ multiple methods of managing the weed, urges Syngenta field technical manager and grass weed expert, Iain Hamilton.

These include cultural methods, chemicals, and the sometimes-overlooked technique of correct spray application – all with the target of achieving more than 97per cent control to stop populations increasing, he adds.

“There is a lot of talk about ‘stacking’ when it comes to managing black-grass,” explained Mr Hamilton, who highlighted the UK’s increasing black-grass problem at this year’s Cereals Event.

“Clearly, stacking different pre-emergence herbicides together plays an important role. Indeed, we have seen that tank-mixing the herbicide Defy with a flufenacet-based treatment has typically boosted control by 20per cent in trials. But we are encouraging growers to think much wider than this.

“It should also be thought of as stacking all the other available tools together in appropriate ways – and doing this all through the rotation,” he added.

Among the cultural strategies to consider, said Mr Hamilton, is to start by re-appraising which crops are included in the rotation, and then opting for crop varieties that are more competitive against the weed.

“Spring cropping, for example, can achieve around an 80per cent reduction in black-grass levels,” continues Mr Hamilton, “depending on the frequency it’s used and the time of sowing.

“Also, with winter cropping, choose varieties that are better able to suppress the weed. In wheat, competitive varieties can reduce black-grass by 27per cent. Alternatively, with its vigorous spring growth, around 90per cent fewer black-grass seeds were produced per metre squared in Hyvido hybrid barley compared with winter wheat in independent research – potentially returning 90per cent fewer seeds to the soil.”

After crop choices, Mr Hamilton urges growers to plan cultivation methods at an individual field level, rather than adopting a blanket approach. “Ploughing will bury shed black-grass seed, and can reduce levels by 67per cent. But if you use it in the wrong field there’s a risk of bringing previously buried black-grass seed back to the surface. So in these fields minimum tillage may be better – but it must be used with stale seedbeds before drilling,” he insisted.

“After cultivating, delaying drilling will also allow more time for black-grass to emerge and be controlled in stale seedbeds. Plus, residual pre-emergence herbicides can be more effective when applied later – due to more favourable soil conditions.

“With post-emergence herbicides, make sure they are applied at the correct time to maximise their efficacy.

“Finally, with both pre- and post-emergence herbicides, don’t overlook factors such as sprayer speed, boom height and nozzle choice. Spray application is something Syngenta has done a lot of research on. Getting it right can improve black-grass control by those important last few per cent.”