Arable News

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Black-grass problem covered in heavy land spring cropping trials

A ‘Black-grass Masterclass’ was organised by Innovation for Agriculture (IFA) and RASE at the Suffolk Showground

Ahead of this autumn’s weed control strategies getting into full swing, a ‘Black-grass Masterclass’ was organised by Innovation for Agriculture (IFA) and RASE at the Suffolk Showground, Ipswich. Dominic Kilburn attended.
Even in late winter cover crops continue to produce biomass above and below ground.
Growers contemplating the use of a spring crop on parts of the farm where black-grass is becoming an unsustainable problem should consider drilling a cover crop this autumn to bridge the gap between harvest and drilling in the spring.
The right cover crops can deliver a highly successful black-grass control programme, improve soil condition and structure and facilitate minimal disturbance/direct drilling of the spring crop.
That’s according to Agrovista technical manager Mark Hemmant (left), speaking at a ‘Black-grass Masterclass’ event staged at the Suffolk Showground in Ipswich recently.
He said that cover cropping was the missing piece of the black-grass jigsaw where spring cropping is part of the rotation. “Spring crops are the most reliable way of dealing with black-grass but it’s not so easy to grow them on heavy land and can be challenging,” he explained. “But use of cover crops can help to extract moisture in winter and improve soil structure for successful direct drilling in the spring – the latter required so as not to encourage any black-grass seed germination within the freshly sown spring crop.”
However, Mr Hemmant pointed out that not all cover crops are the same. “You want to be looking at a cover crop that doesn’t smother black-grass as it establishes in the autumn. The cover crop must allow black-grass seed to germinate with it so that a split herbicide treatment can be used in the spring to kill the cover crop and then the black-grass,” he stressed.
Agrovista recommends its own cover crops for autumn and winter use including black oat combined with common vetch, or black oat and berseem clover. While Mr Hemmant acknowledged that there are other black oat and vetch varieties on the market, it’s a case of “buyer beware” as some are not suitable for sowing in August and early September, he warned.
Low cover crop seed rates allow black-grass to germinate during its key germination period.

Rooting habits
According to Mr Hemmant, both black oat and vetch have a high biomass rooting structure which continues to grow into winter although, particularly in the case of vetch, it needs to be sparsely planted in the autumn to allow the black-grass to germinate. “Cover crop seed rates need to be considered carefully and reduced to keep crops sufficiently open.
“Cultivate, drill them to a depth of 5cm and roll,” he added.
Berseem clover can be grown in combination with black oat but also as a companion plant with oilseed rape, he continued. It has a big tap root which benefits soil structure, it has quick but not big autumn growth above ground, and dies off at the first frost.
“Trials comparing oilseed rape condition grown with, and without, companion crops have shown improvements from the better drainage and soil structure provided by the companion crops,” he suggested.

Heavy land trials
Agrovista’s Northamptonshire-based Project Lamport is a heavy land rotational project aimed at developing new ways to control black-grass that still enable combinable crops to be grown.
Direct drilling of a spring crop into structured soil and cover crop residue.
One of the project’s aims is to develop a way to reliably drill spring crops on heavy land which has a history of highly resistant black-grass populations, min-till cultivation and winter cropping. Indeed, in June 2013 a crop of oilseed rape failed at the site following the wet autumn of 2012 and black-grass infestation.
In year 1 of the project, in July 2013, the site was ploughed (for the first time in 10 years) and black-grass heads counted a year later in 2014.
“Where winter wheat had been grown without herbicide treatments, black-grass head counts were 550/m2. This compared with 55 black-grass heads/m2 in wheat combined with a full programme of herbicides,” explained Mr Hemmant.
“Where stale seedbeds had been implemented and spring wheat the choice of cereal, black-grass head numbers fell to 15 heads/m2, but where the Agrovista cover crop was used ahead of spring wheat, numbers fell to 2 black-grass heads/m2.”
The latest results from the project (2014/15 season), and only recently released, demonstrated that the untreated second winter wheat now had 2,000 black-grass heads/m2; second wheat with herbicides 274/m2; stale seedbed followed by spring wheat 36/m2 and Agrovista cover crops followed by spring wheat had less than 4 black-grass heads/m2.
“The second wheat produced a very high black-grass seed return compared with autumn-sown cover crop and spring wheat which produced a very low seed return,” he pointed out. “Yes the spring wheat was lower yielding (8.6t/ha) compared with the winter wheat (10t/ha) but it was much cheaper to grow,” commented Mr Hemmant.
“We also looked at fallow in Year 1 followed by winter wheat (with or without herbicides?) in year 2 and this resulted in 36 heads/m2,” he added.
He concluded that the use of Agrovista cover crops, in combination with direct drilling of spring wheat, had been very successful in both years of the project; reducing the number of black-grass populations and improving the condition of the soil, while at the same time allowing the growing of profitable crops.

No quick fixes
Don’t assume if your grass weed control strategy worked well this year that it will be similarly successful again for next season.
That was the warning from grass weed research scientist Dr Stephen Moss (of Stephen Moss Consulting) left, who suggested that this was not the autumn to ease up on black-grass control.
Dr Moss said that black-grass resistance to herbicides is increasing and that quick fixes on farm are not the answer; rather a three to five year strategy was required to tackle it. “There’s been an 18-fold increase in the amount of oilseed rape being grown on farm in the UK since 1975 and a 10-fold increase in winter wheat sown in September, so we shouldn’t be surprised.
“Autumn cropping and early drilling make a huge difference in the amount of black-grass as more now comes up in the crop rather than pre-sowing,” he added.
He pointed out that almost every farm in England with black-grass has resistance to herbicides, although not every product, and he suggested that growers will have to make best use of current chemistry as no new active ingredients were on the horizon.
“There is resistance to all the main pre-emergence herbicides, although partial in many cases, however it does seem to be increasing slowly.”
Dr Moss said that understanding black-grass biology underpins the approach to controlling it via non-chemical methods and these included the following key points:
– 80 per cent of black-grass emergence is in the autumn
– Depth of emergence is from less than 5cm
– Seed decline when buried is relatively rapid (74 per cent/year) but growers are starting with high volumes on their farms. Data suggests that only 3 per cent of seed survives 3 years of burial
– Seed shedding patterns: from mid-June in winter wheat and a little later in winter barley, but most is shed just prior to harvest

Shallow stubble cultivations
Dr Moss said that Danish research work has demonstrated that while it is popular for growers to cultivate stubble immediately after the combine to stimulate grass weed germination, it may be better to delay that action. “As long as there is some moisture, black-grass seed will germinate on uncultivated stubble and so it’s questionable as to how much shallow cultivation will help,” he commented. “It may simply increase the likelihood of encouraging older black-grass seeds to germinate from previous years but help preserve freshly shed seeds,” he added.
“We don’t really know enough about the relative benefits of shallow cultivations under different weather conditions and it’s what comes up in the following crop that’s important, not so much what comes up beforehand,” he continued.
“Possibly the best cultivations are those that give you the best seedbed for drilling a wheat crop in mid-October and which also provide the best conditions to maximise the efficacy of pre-emergence herbicides which tend to work better in October than September. I understand that there are conflicts in terms of field operations at that time of the season, and we don’t have all the answers, but drilling at that time could be the driving force for getting on top of black-grass.”
He also referred to AHDB Cereals & Oilseeds-funded trials work carried out by NIAB TAG (2010-2014) that resulted in 33 per cent less black-grass plants/m2 being found where autumn drilling was delayed by three weeks from mid-September. Results also showed 50 per cent less black-grass heads/m2 and 25 per cent additional control from pre-emergence sprays used.
“Each black-grass plant is 55 per cent less competitive in late October compared with late September drilled crops,” he added.

Autumn to spring
Turning to the benefit of spring sown crops in the battle against black-grass he highlighted that Rothamsted trials had shown a mean reduction of 88 per cent in the amount of black-grass when changing from autumn to spring drilling, across five different years between 2001-2012.
“Again, spring cropping is not a complete solution and if most of your black-grass germinates in the spring, then it’s clearly not the answer. But growing two or three spring crops in succession can be very effective.
“Fallowing or grass leys is also a consideration for growers but one year of either of these is not enough. Two to three years is better but grass must be well managed to prevent seed return. Alternatively, a flexible approach to spraying off black-grass patches in early June within crops for several years if necessary – a sort of ‘patch fallow’ – can prove very effective.”
For growers in non-traditional black-grass areas, such as northern England, Wales, Scotland and Ireland, where signs of resistance may appear due to contamination via seed lots or straw, they should target patches with a sprayer or knapsack (if only small patches), or hand rogue, where possible each summer, he advised.

The sky’s the limit
Drone operating company Ursula Agriculture was represented at the event by Alex Dinsdale (left), and he suggested that the company’s UAV fixed wing aircraft (compared with rotary or manned alternatives) was the most suitable for monitoring and recording black-grass occurrence on UK farms.
According to Mr Dinsdale the Ursula fixed wing drone can cover approximately 40ha (100 acres) in 30-45 minutes of flying, before producing a digital map for farmers to then use for identifying and then spraying off black-grass infestations and patches.
Operations are usually carried out in May and June when black-grass is appearing above wheat crops.
Mr Dinsdale said the system could also offer crop performance monitoring – highlighting the best or worst performing crops in individual fields – with a view to better nutrition planning.
Suited to enterprises of 200ha (500 acres) and larger, costs can vary between #10-#20/ha.

Cover crop advantages
– Low seed rates allow black-grass to germinate in the cover crop
– The right cover crops have the ability to produce high biomass later in the autumn and winter both above and below ground
– Easy to kill prior to planting the following crop
– Soil structure to facilitate minimal disturbance drilling
– Roots and residue minimises soil disturbance when drilling the spring crop
– Will not create a pest, disease or volunteer problem in following crops

Benefits of delayed autumn drilling
– Less black-grass in the crop as more can be destroyed pre-drilling
– Fewer black-grass heads and less seed return
– Better control from the herbicide programme
– More of a benefit if delay from mid-Sept to the first half of October
– Growers must be flexible as every field is different and every year is different Don’t delay drilling in all fields, but target the worst affected

  • Written by: Farmers Guide
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