New trials in Oxfordshire are showing how crop competition can make a valuable contribution to black-grass control within an integrated strategy.
It is the fourth year of the Hutchinsons trials at the Mollington black-grass centre near Banbury, where weed populations have fallen from 1,500 plants/sqm to 50 plants/sqm, by focusing on cultivations, soil health and rotation.
The dramatic reduction in black-grass pressure has allowed winter wheat to be reintroduced to the site for the first time in four years and Hutchinsons agronomist Toby Kellie is investigating how wheat can be managed to suppress black-grass, through drill choice, variety and seed rate.
Growers saw this work first-hand at an open day on March 14, where Mr Kellie and Hutchinsons Seed Business Development Consultant David Neale highlighted early findings from plots that will be monitored through to harvest.
In one field, three drills were used to sow Skyfall at 450 seeds/sqm last October, allowing comparisons of machine characteristics. These included a Weaving GD 8000T, a Sky EasyDrill HD and the farms Väderstad Rapid. The latter was preceded by one pass with a custom-built Surface cultivator as the Väderstad could not direct-drill well enough to be a fair comparison.
Mr Kellie highlighted a clear correlation between soil disturbance at drilling and resulting black-grass pressure, with the Weaving drill causing least soil movement and lowest black-grass germination. The Väderstad/Surface technique moved most soil and was rated worst for black-grass.
However, extra soil disturbance to create a tilth in the clay loam had clear benefits for crop establishment, which was highest in the Väderstad plot (69% and average 2.3 tillers/plant) and lowest (57% and 1.2 tillers per plant) in the Weaving trial.
"One drill isn't necessarily better than the other, but working characteristics are worth considering, No-disturbance direct drilling has a place, providing it's not at the expense of crop establishment. There's a balance between creating conditions for good establishment without stimulating too much black-grass.
"Due to the dry autumn, we didn't cultivate a month prior to drilling as per our strategy, but this would have created a better tilth for the Weaving to perform better."
Cultivating the Väderstad plot so close to drilling put it under greater black-grass pressure, which was exacerbated by not being able to apply residual herbicides until post-emergence, he added.
Fortunately, favourable conditions in late autumn/early winter meant residuals worked "immensely well" and negated this pressure, but he acknowledged other years could have been different.
Variety choice and seed rate
A separate field after potatoes hosted a trial comparing four wheats - Crispin, Skyscraper, Sundance and Costello - at two seed rates (400 and 500 seeds/sqm).
Although black-grass risk was higher given significant soil movement in the preceding crop, excellent residual herbicide performance reduced weed pressure across all plots, Mr Kellie noted.
However, early observations suggested Crispin, sown at 400 seeds/sqm, had performed better for establishment vigour, tillering and black-grass suppression, Mr Neale said.
"Speed of establishment, and tillering in autumn and spring, are key to maximising crop competition, as the quicker crops prevent light getting to black-grass, and the less impact it has on yield
"Crispin is the go-to variety from what we've seen so far, with 91% establishment, 364 plants/sqm in autumn and 981 tillers/sqm in spring."
Skyscraper also tillered well, although lower establishment meant less early crop competition. The variety's extra height could help smother black-grass later though, he noted.
Mr Neale reminded growers that differences between varieties and seed lots meant it was crucial to drill by seed number rather than weight.
"At the same seed numbers you can easily get 50kg/ha difference in physical seed weight per hectare. This is critical in planning the right variety for drill date and tillering structure. We can easily provide our growers with this information."
Learn about our upcoming Mollington black-grass demo day [HERE]