Hold your nerve: keep wheat drills under wraps to beat black-grass

Hold your nerve: keep wheat drills under wraps to beat black-grass15 September 2022

Farmers with a known black-grass burden shouldn’t be lured into bringing their winter wheat drilling date forwards just because large parts of the UK have seen improved soil moisture levels following the dry, early harvest. That’s the advice from Mike Thornton, head of crop production for agronomy firm ProCam, who recommends that growers should hold their nerve and delay drilling for as long as is practicably possible.

“Rushing out to drill just because we’ve seen some decent rainfall events in the last few weeks would be counter-productive,” Mr Thornton says. “Instead, delaying drilling until mid-October, or even into November where weather conditions allow, provides a fantastic opportunity to create some really good stale seedbeds after this year’s early harvest, especially for those growers who need to control burgeoning black-grass populations.”

Whilst a significant proportion of wheat growers with a severe black-grass problem might aspire to delay their drilling date for as long as possible, it remains to be seen how many will actually hold their nerve: “There’s a lot of talk about how this year might mirror the historic summer drought and infamously wet autumn of 1976,” Mr Thornton says.

“Admittedly we could be heading into another wet end to the year, but the truth is no-one really knows what the weather might hold. What we do know however, is that delaying drilling to enable weeds to germinate so they can be controlled before the next crop is planted is still the best tactic on high-risk land. It therefore makes sense to play the long game and to keep the brakes on the seed drill until the first flush of weeds has been eliminated.”

Yields needn’t suffer

For growers concerned that delaying drilling can affect yield, a multi-year ProCam trial at the company’s trials hub at the Stockbridge Technology Centre near York, in which different winter wheat varieties have been drilled at monthly intervals from September onwards, has shown that although drilling date can affect yield, it was not crops drilled in September which produced the best yields, but those sown in October.

“That might sound illogical,” Mr Thornton explains, “but it actually makes a lot of sense. That’s because, compared with September, there’s likely to be more soil moisture for germination in October and seedbeds should be more weathered down to aid crop establishment. More grass weed seeds should also have germinated by October therefore allowing for better control before planting commences.

“Residual herbicides should also be more effective and persist for longer in October’s cooler, moist soils, which will be of benefit to later-drilled crops where there may only be time to make a single treatment compared to earlier-sown crops which might need both pre- and peri-emergence applications. For both strategies, drilling cereal seed to the correct depth is crucial from a crop safety perspective, so it pays to scrutinise herbicide product labels before drilling commences.” 

Mr Thornton says later-drilled crops might also face a reduced threat from barley yellow dwarf virus (BYDV) infection – due to lower air temperatures reducing the activity of disease-vectoring aphids – with later-drilled second wheats also less likely to be affected by take-all. “In both cases there’s no guarantee later drilling will reduce the level of risk, especially as it’s unlikely temperatures will suddenly drop off a cliff over the next few weeks, so both risks will still need to be monitored. However, these are added potential benefits for growers whose resolve to delay drilling might be wavering.”