Arable News

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Crop diversification vital in the war against weeds

One a conventional grower, the other organic, have developed similar strategies for weed control

Two farmers; one a conventional grower, the other organic, have developed similar strategies for weed control, delegates heard at the recent BCPC Weeds Review 2014 event, held at Rothamsted Research. Dominic Kilburn writes.Cambridgeshire farmer Ed Banks said that he inherited a ‘total black-grass’ situation on his farm.It may seem odd, initially, when a grower derives a certain level of satisfaction from seeing patches of black-grass appearing on yield maps of fields on his farm. However, Ed Banks says that when he first inherited the family farming business Thomas Banks & Partners in Cambridgeshire back in 2007, whole fields were infested in black-grass and, in many cases, crops had to be written off before progress could be made.Now, nearly eight years on, he says that a focus on crop rotation and cultivations, in particular, has meant that there has been as much as a 50 per cent reduction in black-grass on the farm.Speaking recently at the BCPC Weeds Review 2014 event at Rothamsted Research, in Hertfordshire, Ed, who farms 1,200ha (3,000 acres) just south of Cambridge, said that he inherited a ‘total black-grass’ situation. “We were seeing whole fields of black-grass and not just patches. Attention to detail in the past had not been good, and I haven’t been able to use any post-emergence herbicide control since,” he explained.Cropping on the predominantly heavy land farm had previously been based on a wheat/wheat/oilseed rape rotation and it had been the break crop that had caused significant difficulties with black-grass.”Our break crops weren’t good and I was finding that oilseed rape was allowing black-grass in. As a result, our first wheats were dirtier than our second,” he pointed out.“This was exacerbated in the 2012/2013 season when we got a really wet autumn in 2012 – highlighting problem drainage areas – and the rape just didn’t grow. As a consequence, the following wheat was infested with black-grass and had to be sprayed-off and replaced by spring barley the following spring.”According to Ed, a whole farm approach to combating black-grass was required, which included a revamp of cropping plans and a change in the way the land was cultivated. “It was clear that our wheat and oilseed rape rotation wasn’t working and with the loss of post-em herbicide control, we were running out of options.”With some lighter land on the farm, sugar beet was introduced into the rotation, as was spring beans for the worst affected black-grass areas, and spring barley too – the latter performing very well on the farm over the past year being grown on some of the black-grass infested wheat land.”Introducing sugar beet gave us different chemistry to be able to use against black-grass but we found it just as hard to control,” commented Ed, “but it did give us the option of hoeing,” he added.Wide crop row spacing was also introduced into the oilseed rape establishment system – seed delivered to the soil off the back of a subsoiler while leaving the area between the tines undisturbed to reduce weed establishment. In addition, all fertiliser was applied ‘in-the-row’ to better target nutrition to the growing crop, and to aid establishment and weed competition.According to Ed, machinery on the farm is now GPS-operated which allows the use of a precision-guided Micron Varidome ‘hooded’ spraying system to apply glyphosate between the rows in both sugar beet and OSR.As well as a good opportunity to hit black-grass with different chemistry, it also delivered a 70 per cent reduction in herbicide use and the long-term aim on the farm is to vari-rate pre-em spray applications in wheat for a more targeted approach to control black-grass.Cultivations
The second major area of change required to address the black-grass problem was the farm’s cultivation strategy, which had traditionally been based on the plough. However this was causing poor, cloddy seedbeds, which impaired the efficacy of pre-em herbicides, as well as drying ground out and reducing the flushes of black-grass, he explained.A Vaderstad Carrier cultivator, similar to this, is used to remove as much black-grass as possible before drilling takes place at Thomas Banks & Partners.“We changed to min-till and we are now starting to see benefits in terms of improved seedbeds, and we also delay our wheat drilling,” said Ed.”I try to get in the field as soon as possible after the combine with a Vaderstad TopDown cultivator followed by a Carrier disc and press about a month later, and this will kill up to about 50 per cent of the black-grass that has established. “We then spray off with glyphosate before drilling wheat to a depth of 4cm.
“If there’s a chance of another light cultivation prior to drilling then we’ll do that but the pre-em applications are then our last opportunity to take out black-grass,” he added.On over-wintered land ahead of spring cropping, Ed said that he would keep cultivating before spraying off prior to drilling. “Glyphosate is obviously key for us and I would be concerned if regulation meant that we had to do without it, but we use cultural control as much as possible.”Certainly we have found that if winter wheat is followed by winter wheat in the rotation, and drilled early, then wheat will not be the best crop on the farm in terms of gross margins.”For growers who find themselves in a similar situation as us, my advice would be to be brave and desiccate wheat crops that are infested with black-grass, replacing them with a spring crop for the long-term benefit of the farm.”Changing our cropping and cultivations across the farm, and using new technology in wider row crops, for example, has worked for us and stopped the weed seed return. We have reduced black-grass on the farm by as much as 50 per cent over the past five to six years while, for some of my neighbours, it keeps getting worse.”Learning from organicAlso speaking at the event was organic farmer and agricultural consultant, Stephen Briggs (left), who emphasised that in a farming system where herbicides were not permitted, crop diversification was key when considering weed management.Organic systems rely on a wide range of cultural and physical systems, and management approaches to weed control, he commented. “However I believe there are real opportunities to adapt organic technologies and approaches into conventional farming systems,” said Stephen, who farms organically on 240ha (600 acres) near Peterborough, Cambridgeshire and is a consultant with farm advisory business Abacus Agriculture.”The underlying principle for weed management on organic farms is crop rotation and diversity and so we have to accept a certain level of biodiversity, although this has to be balanced with the economics of farming and the production of an acceptable crop,” he explained.”The less diversity in crop choice then the more weed pressure there is in fields,” he added.Stephen suggested that a starting point for organic growers when considering weed control options was to look at historic land use, weed problems and cropping, and to see what the weeds were telling them in terms of indicators of soil physical and mineral conditions.Some weeds for an organic farmer were acceptable (and beneficial to organisms), such as knotgrass redshank and chickweed, however there were those such as charlock, wild oats, brome and black-grass that were not, he suggested.”Weeds are the number one problem for most organic farmers and there’s no silver bullet, but management options include rotation, crop choices (type and winter versus spring), in-crop agronomy and between crop agronomy (green manures, catch crops and under-sown crops).”He said that choosing a crop such as oats instead of wheat could lead to a significant reduction in weeds and those varieties with early development and a prostrate growth habit provide distinct advantages.”Most organic farms will also have livestock and this is used as a tool for adding grass leys into the system as well as cattle, sheep and pigs crop grazing for weed management.”Cultivating stale seedbeds, he said, was an important tool in reducing the number of weeds in the following crop and it was best employed with later autumn and spring sowing.”Organic growers give more time to producing stale seedbeds by drilling later – drilling early in a tight window at the end of the summer increases weed numbers,” he said.”Wheat usually goes in from mid-October and winter beans from mid-October into November. Not drilling anything in September allows far more time for weed flushes to be taken out by cultivation, and time also needs to be taken ahead of spring drilled crops.”Stephen pointed out that higher seed rates on organic farms – typically 200kg/ha for winter wheat and 250kg/ha for spring wheat – also played a part in weed suppression, while wide-row drilling of wheat, oats and peas enabled in-crop hoeing or tined weeding to take place.”Most combinable crops can be grown on wide rows from 20-25cm without detriment to yield and performance,” added Stephen.  Organic farm preventative weed management options: at a glance
– Crop rotation
– Choice of crop species
– Choice of variety/cultivars
– Use of stale seedbeds
– Time of sowing
– Seed quality and rates
– Crop architecture
– Crop vigour
– Under-sowing in cereals and mixed cropping
– Inter- and bi-cropping
– Allelopathy


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