Carefully targeting cultivations and selecting more competitive varieties will help wheat growers maximise cultural black-grass control this autumn.
Trials at the Hutchinsons Mollington Regional Black-grass Centre, at CA & A Hall & Son's farm near Banbury, Oxfordshire, first reported in A&AF in June, are now showing there can be significant benefits to weed control from using well-timed, shallow cultivations and growing more competitive varieties.
But as fields begin to be cleared this harvest, Hutchinsons Technical Manager Dick Neale urges growers to be patient with cultivations to maximise their benefits.
Most black-grass will generally not germinate until the third week of September, so stubbles should be left until then, he says. Hot, dry, sunny weather degrades seeds left on the surface, plus some will be eaten by birds and insects.
“There's no point moving any soil until mid-September at the earliest, and when you do, only move the top 50mm to avoid bringing up old seed or burying fresh seed. This also helps protect the most biologically active layer of soil,” he says.
A light cultivation at the optimum time can 'make the world of difference' to black-grass control, by stimulating germination and encouraging a strong flush of weeds that can be sprayed off before drilling, Mr Neale adds, also pointing out that cultivating too early increases the risk of seedbeds becoming too fine by the time fields are drilled later in autumn.
The drill trial at Mollington reinforced the benefits of a shallow cultivation and showed direct drilling to be less effective when faced with black-grass pressure. Three machines – a Weaving GD 8000T, a Sky EasyDrill HD and the farm's Väderstad Rapid – were compared in a field of Skyfall, sown in October at 450 seeds/m2.
The Weaving and Sky plots were both direct drilled, but due to difficulty direct drilling with the Väderstad, it was preceded by a single cultivation using a custom-built surface cultivator immediately prior to drilling.
This extra soil disturbance mineralised nitrogen and created a better tilth, which resulted in the most black-grass emergence within the crop of all three drills, but also the highest crop establishment and tillering – giving greater crop competition. This was reflected by the highest wheat ear count of 753/m2 this spring, well above the 546/m2 and 569/m2 in the Sky and Weaving plots respectively.
As Hutchinsons agronomist Toby Kellie explains, this crop competition meant that although more black-grass plants emerged within the Väderstad plot, each produced fewer tillers per plant. In contrast, the low soil disturbance in the direct-drilled plots stimulated less black-grass germination, but the lower crop competition meant those weeds tillered more.
“Overall, it resulted in the same average black-grass ear count of 10/m2 in all three plots, although it occurred in different ways. This is a dramatic reduction from four years ago.”
He acknowledges cultivating the Väderstad plot so close to drilling was a necessity given the conditions last autumn and was not ideal, as black-grass emerged with the crop.
“Fortunately, we achieved excellent results from our autumn herbicide.
“In future, the solution for all drill types is to reduce the initial black-grass plant population by cultivating earlier to promote that initial flush in a stale seedbed before drilling, then use crop competition to reduce tillering of remaining or later-germinating plants.”
The variety and seed rate trial demonstrates how crop competition can further reduce black-grass pressure.
"If you're going to drill later for black-grass control, you have to choose a variety which can compensate for the issues this may raise, through more vigorous establishment and strong tillering,” Hutchinsons Specialist Seed Consultant David Neale explains.
“But any variety must suit your location and soil type, so it pays to try a few options and seed rates.”
On the silty loam at Mollington, Costello, LG Sundance, KWS Crispin and LG Skyscraper were compared, each sown at two different seed rates (400 and 500 seeds/m2) in mid-October after potatoes.
He adds: “KWS Crispin really stands out, producing a good number of tillers at both seed rates and was very competitive against black-grass in autumn and spring.
"Having a vigorous crop that establishes well early in the season is key to competing with autumn-emerging black-grass, but the crop has also got to get away well in the spring to stand the best chance of competing with spring-emerging weeds.”
In contrast, LG Sundance lacked the tillering and competitiveness of other varieties in this trial, although it did retain more tillers at the lower seed rate, providing some compensation for final ear count, he notes.
Beware spring emergers
Mr Kellie points out that although excellent weed control was achieved last autumn, a significant amount of black-grass emerged in spring. These plants tended to be smaller, with fewer tillers than autumn-emerging black-grass. However, they could still return a large amount of seed.
Post-emergence herbicides in January/February can be effective but should not be relied on, especially as it can be hard to travel on fields at this time.
“Crop competition is therefore our main tool for controlling spring-emerging black-grass, so it's vital we do everything to maximise this, whether through improving soil health, cultivations, variety choice, or other agronomy," he adds.
With that in mind, fellow agronomist Toby Page says next season's trials will again look at different drill types (namely disc and tine drills), but also consider other ways to boost establishment.
This includes trialling tailored nutrient seed dressings to improve autumn vigour and competitiveness, plus a look at the new variety KWS Extase, known for its high biomass. Hybrid wheats will also be tested to see how their low seed rates fit into black-grass situations.
Mr Page says: “Our aim is to produce a rounded package of agronomy advice showing the range of cultural options available for black-grass control.”
- Leave autumn cultivations until at least mid-September
- Restrict cultivations to the top 50mm
- Delay drilling until mid-/end-October to control autumn-emerging black-grass first
- Maximise black-grass suppression through crop competition
- Select competitive, high-tillering varieties with strong autumn and spring vigour
- Use appropriate seed rates to maximise competitiveness
- Consider other ways to promote autumn vigour e.g. seedbed preparation, nutrition
- Beware of spring emerging black-grass-consider post-em herbicide and maximise crop competition.