Arable News

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Field Focus – August 2013

Not surprisingly, our agronomists’ thoughts are turning to black-grass ahead of what could be a critical autumn for its control

Not surprisingly, our agronomists’ thoughts are turning to black-grass ahead of what could be a critical autumn for its control. Dominic Kilburn writes.Notts and Lincs
The first thing growers should ask themselves ahead of drilling wheat this autumn is should winter wheat be drilled at all or is a spring crop, or even fallow, a better option for long-term grass weed control, said Nottinghamshire and Lincolnshire-based Arable Alliance agronomist Andrew Wells (left).  Growers mustn’t stumble blindly into drilling a winter crop in fields where black-grass is a real problem, he stressed.”I am going to ask growers to start drilling in their cleaner fields first and, if they have to drill wheat into fields known to be bad for black-grass, they should delay drilling these into October and make the maximum use of stale seedbeds and glyphosate.”Where black-grass is very bad, then they could plan to drill a spring crop, making full use of repeat glyphosate applications to stale seed beds during the autumn,” he added.Andrew said that he hoped that black-grass dormancy would not be as bad as last autumn, although with a range of black-grass seed in the ground shed over several years, it was difficult to predict. “I do expect there to be more control from stale seedbeds this autumn compared with last,” he suggested.He reckoned growers would have to be realistic about when they planned to get the bulk of their winter wheat crop in the ground, and he advised delaying until at least late September/early October to give a chance for black-grass control beforehand. Where black-grass isn’t an issue then a mid-September drilling date is perfectly acceptable. “I would also be happy to push the seed rates up for the later drilling slot to add to the crop’s competitiveness,” he added.Andrew conceded that although delaying drilling was the right thing to do where black-grass was a problem, if as a consequence pre-em sprays were then applied to poor seedbeds and an autumn applied early post-em spray was missed because of deteriorating conditions, then growers could once again find themselves in a difficult situation. “If missing an autumn post-em application means that the next time you get near the crop with a herbicide is Atlantis (mesosulfuron + iodosulfuron) in April, that is not going to give good enough grass weed control in most situations.”What we need for black-grass control is a good stack of actives at both pre- and early post-emergence, including Avadex (tri-allate) if possible, with Atlantis being included in the early post-em application,” he said.”There are serious questions over Atlantis’ efficacy when applied to large black-grass plants in the spring, but autumn applications to smaller weeds are often more effective,” he added.”On the positive side many growers have spring sown crops to harvest this year so there are options to make use of farm-saved seed where spring crops are planned for sowing for harvest 2014, giving useful savings compared with the cost of purchased seed. As with all farm-saved seed, get it tested for germination, vigour and diseases to make sure it is good enough to use and to determine if a treatment is required.”Northants, Beds and Cambs
Before any crop management decisions are made, consider the likely effect they will have on black-grass.That was one of the key messages from 3-Shires AICC agronomist, Gerald Collini (left) who advises on land in Northamptonshire, Bedfordshire and Cambridgeshire.”Whatever the decision, from cultivations through crop, variety, planting time, chemical choice and timing, make the likely effect on black-grass the priority,” he advised.Gerald said that to have any chance of success with black-grass this autumn, there were two clear routes to go down; either keep black-grass seed near the surface for stale seedbed activity or plough it down properly to keep it there for a few years.Speaking in mid-late July, he said that if the dry conditions remain, then ploughing may not even be an option on the heavier land. “We know that conditions can change very quickly, but the hot weather has fractured the chalky boulder clay beautifully and has done a lot to repair the structure of damaged soils,” he commented.”After last year’s problems, delaying drilling and waiting for black-grass to germinate before spraying off with glyphosate won’t be popular but there aren’t many other options,” he said.”On clean fields, drilling can proceed at the normal time from mid-September, growers can apply the usual residuals if conditions allow and control should be sufficient, but on the less clean fields, where black-grass is a problem, this won’t be enough. At least one spray-off before planting is vital now that Atlantis can no longer be relied upon. It can still do something if used early, pre-tillering, but it’s not cheap when only 10-20 per cent control is the best achieved.”Gerald said that many growers will have held off from drilling last autumn and found, to their cost, that they failed to get crops in the ground because of the bad conditions, but he suggests that there is the potential to grow high yielding spring wheats which offer a flexible planting date and the opportunity to carry out several stale seedbeds beforehand.”We need to be thinking about using crops to control black-grass so why not plant a crop that can have a delayed drill timing?” he questioned.He added that spring barley also looked a good option with crops faring well this season despite no preparations done to seedbeds over winter and the delayed start. “Spring cereals offer the opportunity for a serious reduction in black-grass numbers and seeding potential as well as an easy entry for oilseed rape,” he added.Essex and Herts
Advising on land in north Essex and east Hertfordshire with Samco & Shrim Farmers, AICC agronomist Jamie Mackay said that while black-grass is an issue in places, he doesn’t have the large areas of resistant populations that can be found in some parts of East Anglia, but his blackgrass is harder to control with chemistry compared with fifteen or twenty years ago.”We were certainly challenged in the autumn and on the larger farms where they had to get on the drill and keep going, some missed the opportunity for stale seedbeds and some pre-ems last autumn.”As a consequence post-winter applications of pendimethalin + Atlantis really struggled to gain control of black-grass in the spring,” he commented. “The mix hasn’t failed altogether, but the trend for reduced efficacy is one we’re finding year on year in our resistance testing, which in reality is confirming what we’re finding by field observations.”Jamie said that the message he strives to give his growers is for them to be extremely cautious about sowing winter cereals much before 20th September, unless they really have to on account of very large acreages. “And they should leave the ‘dirtier’ areas to the end of the drilling programme,” he added.”I am trying to encourage a glyphosate spray before drilling followed by Avadex granules and then a flufenacet/pendimethalin/DFF application probably at early post-emergence. It’s nothing new but it’s worth reiterating what is required. The hope is in some way to reduce our reliance on spring Atlantis mixes.”If the black-grass situation is bad we will move to a spring crop as we want to build the cultural control element to bring the black-grass numbers down – one man on a tractor can’t do it all,” he stressed.In terms of spring cropping options, Jamie said that beans and linseed are featuring more heavily in his rotations for the coming season, the latter providing very good weed control options.
*Jamie can be contacted at: [email protected]


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