Management flexibility is perhaps the most important priority in black-grass control reveal the latest long-term agronomy trials at Stow Longa say Agrii.
Established in 2014/15 in the wake of the Centre’s five year cultivations and drilling strategy research, the trials involve five, 1 ha ‘fields’ subject to a range of different rotations and cultural regimes.
Two years into the work, yield and gross margin as well as black-grass population comparisons between rotations and regimes are providing a wealth of extra intelligence on the most economic as well as effective weed control.
“In our first year we recorded average black-grass populations varying from zero to 1200 heads/m2 over our five separate fields,” reported Agrii agronomy manager, Colin Lloyd. “At 18 to 285 heads/m2 across the fields in the 2015/16, we saw noticeable improvements from our rotations in three cases and backward steps in two.
“More interestingly, though, the black-grass populations we saw from the 19 main treatments we had across the trial last season varied from 1 to 876 heads/m2. At the same time, the operating margins (including establishment as well as input costs) differed by nearly £1000/ha from -£376/ha to +£567/ha.
“What’s more, the best results in Year 2 didn’t necessarily come from the fields with the least seed return the year before. It all depended on both the crops we chose and the way we established them.
“This underlines the extent to which the good work of one year can all too easily be undone by poor decisions the following season,” Colin stressed. “Encouragingly, though, it also shows that getting things wrong in one year can be overcome with good decisions the next.”
As well as underlining the value of both rotational ploughing after many years of minimum tillage and delaying winter wheat drilling, the 2015/16 trials highlight the importance of rotational choices in long-term black-grass control.
Unsurprisingly perhaps, spring cereals – either after a fallow or another spring crop – stand out as much better for both black-grass control and margin-earning than winter wheat in ground with a history of serious weed problems.
However, even following a zero seed return fallow, the Stow Longa work shows a spring crop will not keep black-grass under sufficient control without the most appropriate establishment management.
In the same way, it points up the fact that two spring crops in a row aren’t necessarily the solution either, although correct management can do much to reduce the weed burden.
“Winter beans look a very interesting proposition,” noted Colin Lloyd. “Their margins may be modest, but in both Year 1 and Year 2 they gave us the lowest levels of black-grass seed return of any crop. An average of 18 heads/m2 last summer following 390 heads/m2 in the previous wheat crop was especially impressive.
“Late August-sown cover crops resulted in higher black-grass populations than either deep cultivation or ploughing in most cases. But a clear improvement in winter wheat yields and operating margins after the covers – even after accounting for their extra costs – suggests they are contributing in other ways.
“Overall, the message coming out of this latest work is clear,” he concluded. “We need to keep sufficient flexibility to respond to our black-grass problems field-by-field, season-by-season with all the cultural as well as chemical tools available to us. We need to see the challenge as a continuous and continuously evolving one rather than something that can be fixed by a simple action or two. And we still have a lot to learn about a number of potentially valuable cultural opportunities – most notably winter beans and cover cropping.”