The term resilience cropped up several times at Hutchinsons’ recent Cambourne blackgrass demonstration day, particularly when it comes to the weed itself.
It shows an uncanny ability to fight back against evolving farming systems, and as it adapts so control strategies need to adapt further noted Hutchinsons technical manager Dick Neale
What has been observed at Cambourne is that while plant numbers have reduced, the productivity of those plants has increased. At the old Brampton site, plant numbers of 400 or 500/m2 were recorded; now it’s 40 or 50 m².
One battle won, perhaps, but those weeds that survive are ‘bigger and fitter’. Blackgrass plants that haven’t been exposed to herbicides or crop competition show remarkable vigour with a tillering capacity not matched by cereal crops.
In addition, the company has observed a protracted emergence of blackgrass into November and even through the dry spring of this season.
One of those adaptions Dick wants to see is seed rates adjusted to row spacing. He pointed out that some systems are as wide as 25cm, yet seed rate often remains the same. “Care has to be taken to ensure the correct spacing down the row so plants grow out rather than upright, so seed rates need to be lowered not increased.”
A focus for work at the Cambourne site is identifying where blackgrass is emerging from within the soil profile. At the site the majority is emerging from 2-4” depth, no surprise Dick noted with the farm’s shallow cultivation approach. “Knowing the emergence zone is critical in how the problem is managed,” he added.
Blends competitiveness boost
Also under investigation are blends. Jade Prince, services specialist, showed single varieties of blends of Typhoon, Dawsum, Mayflower against the three varieties as straights.
The rooting differences between the three resulted in a more diverse profile throughout the soil and boosted surface cover. Jade also pointed out that root diversity is pumping out a range of different root exudates, feeding an equally diverse range of soil organisms, improving soil health.
Diversity was also Jade’s answer when questioned about how to improve organic matter. Using the Terramap system, Jade had analysed the farm’s organic matter, noting that soil data was invaluable to help improve crop competitiveness in problem areas.
Using maps taken from the system, it revealed clay to soil organic carbon ratios being as high as 13 – 1, where the ideal was 1 part carbon for 8 parts clay. “Those areas with spare clay particles can absorb more carbon, an opportunity to improve OM and boost crop competitiveness,” she noted.
John Cussans, weed scientist principle consultant at ADAS, isn’t surprised that things have changed. He pointed out that as better agronomy has improved crop yields, so it has done the same for weeds. “The research data shows the size of blackgrass plants that survive control is increasing. A seedling plant density that delivered four heads per m2 in 1990 has more than doubled. Now it can be ten,” he noted.
Protracted germination
In addition, germination is more protracted. “There’s no big germination bang through reduced soil movement, resulting in more seeds left in the reservoir to germinate later. Coupled with more open canopies which also creates the conditions for later germination. It’s more unpredictable now,” John added.
The field for the herbicide trials had been treated as such, drilled on October 5th at 20 cm spacings, resulting in germination being staggered. Untreated plots had plant counts of 30 m2. “These untreated plots have head numbers above 30 x 4,” he added.
Those plots where a sequenced strategy had been applied offered the best control.
“Here, with the grassweed pressure, the sequence of a tight pre-em and early post-em has worked well. If that early post-em gets stretched to a true post-em, then it has fallen apart. In a September drilled crop, the gap between cotyledons and the first true leaves is around seven days, an October drilled crop ten. That’s how tight the window is. Luckily, I haven’t got to do it.”
John considers in such situations, a well-timed sequencing strategy offering an appropriate active loading was more important than the choice of chemistry. “Here, this has worked better than single pre and post-em applications of the most active products,” he noted.
Drainage. Can you afford not to?
The question of drain maintenance was part of the event. Will Foyle, head of farm business consultancy at Hutchinsons, presented data showing how drainage had shown a significant reduction in seed return and a significant increase in yields and profitability.
It’s not only important for reducing blackgrass but also for supporting crops. The knock-on consequences of poor drainage are increased waterlogging, resulting in areas of stunted or underperforming cash crops, no crop at all, plus a potential harbour for blackgrass. “Blackgrass thrives in wetter soils and where there is little competition,” he said. “Importantly, poor drainage also compromises the ability to travel at optimum times, such as restricting the opportunity to drill or apply a herbicide.”
Taking data from the 23/24 season, he showed that the yield deficit from wetter areas of the field was close to 4t/ha. “Where we had areas of poor or compromised drainage, the spring barley achieved 3.75 t/ha. Where the soil structure allowed agronomic actions to be undertaken, it was over 7t/ha,” he noted.
Allowing for drainage improvement costs of £3000/ha and an adjustment for ploughing to reduce seed return where no drainage has been undertaken, Hutchinsons calculations show a net difference of £400/ha between the two. “The data is a compelling argument for maintaining drains,” Will added.
As is the seed return. Being able to travel when required for optimum husbandry likely to see a seed return of 35% as opposed to 150%.
For those that might be daunted with the task of identifying drains and outlets, Will and Dick had used Omnia to georeference locations from maps produced in 1958, the scouting app taking them to the location in question. “The maps aren’t perfect, so our first dig was a fraction out. But once found, knowing the spacing between the drains, locating others was pretty straightforward.”
