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Arable

Cultural control continues to evolve in black-grass challenge Originally set up as a crop protection trials centre, Agrii’s Stow Longa heavy land site near Huntingdon has evolved more into a major study of cultural control methods in the on-going battle against black-grass. Dominic Kilburn reports on some of the latest findings.

If left untreated, the trials site at Stow Longa has the potential to produce as many as 1,500 ears of black-grass/m2

After 17 years of heavy land black-grass trials at Stow Longa in Cambridgeshire, it’s clear that cultural control methods including cultivation, drilling date and rotation are key drivers for success with difficultto-control resistant black-grass populations. And, while there is no blue print for success – as every farm and field is different – the advice from one expert is for growers to remain flexible in their approach to black-grass control this season. Understand what has been done in the past and then work with your agronomist to answer all the questions, and then establish a strategy for the season ahead, summarised Agrii’s Colin Lloyd (right), speaking at Stow Longa earlier in the summer. “Assess each field. Think about cultivation and rotation, and consider later drilling or drilling in the spring if needs be. There might be a need to ‘spoil’ the planned rotation – perhaps a spring barley instead of a second wheat – but it’s about staying in business,” he said. And that advice is just as pertinent to those in parts of the country where signs of black-grass are being seen for the first time, as well as for those who have been battling it for several years, stressed Mr Lloyd. “Black-grass is an adaptable plant

and resistant black-grass is now widespread in many parts of England and moving into Wales and Scotland,” he warned. “100 ears of black-grass/m2 reduces winter wheat yield by 1t/ha and 400 ears of black-grass/m2 is common on many farms in the UK. This is not sustainable and the reason why black-grass control is so important,” he added. Trials at Stow Longa initially focused on ‘new product’ Atlantis (mesosulfuron + iodosulfuron) before and after its launch in 2003, and there was concern at the time that not all the answers for weed control were going to be found in a can if the product was to fail. In 2008, 97 per cent control of black-grass was achieved with Atlantis at the site compared with around 15 per cent in 2015/16, which, according to Mr Lloyd, if left untreated, has the potential to produce as much as 1,500 ears of black-grass/m2.

Later drilling Cultural control trials began in the early 2000s and later, in 2010, a

There might be a need to ‘spoil’ the planned rotation – perhaps drill a spring barley instead of a second wheat to help combat black-grass, growers are advised.

cultivation and drilling date ‘Five-Year Strategic Project’ also commenced. Over a four-year period (2010– 2015), project trials demonstrated that there was an average of 41 per cent additional winter wheat yield delivered by drilling in October compared with a September drill date – worth an extra £360/ha/year. “Later drilling is driving the benefit for black-grass control,” commented Mr Lloyd. “Growers need to get it out of their heads about drilling early for bigger yields. Yes, that was true before resistant black-grass but that’s not the case now.” He suggested that primary cultivations, whether that be a rotational plough or some other form of cultivation, should take place as soon as possible after harvest to allow for the maximum time for grass weeds to chit ahead of drilling. “Get cultivations out of the way early, then leave the land for about six weeks before spraying off with glyphosate and drilling. “After many years of trials here on a heavy land site infested with resistant black-grass, we have found the six week gap critical. I don’t care whether it’s a high dormancy year or a low dormancy year for black-grass seed. Allow six weeks and that will give you the maximum chit,” he stressed. If you still want to drill something early, then look at a winter barley and not a wheat,” added Mr Lloyd. “Don’t keep scratching the soil with more cultivations to try and get more chits. You must have the resource on farm to drill your entire winter acreage late, otherwise you shouldn’t be trying to do it,” he continued. “If it’s a problem, then there must be a change in the workload to make it happen as you cannot keep doing what you used to do where black-grass is concerned. “Rotational ploughing may still be the ‘cultural control utopia’ but later drilling is driving the benefits,” he said.

By comparison, direct drilling in year 3 – following direct drilling in year 2 and the plough in year 1 – delivered 84 per cent control of black-grass and delivered yields of 7.21t/ha. “Three years on after the start of the project, the plough was still showing its rotational benefit,” highlighted Mr Lloyd. “The difference in the amount of black-grass control and yield was excellent – in this instance (2013) doubling the yield three years after the initial change in cultivation technique,” he explained. “We are trying to understand what all these cultivations mean – but we do know that cultivation and drilling date makes a difference. “You can beat black-grass but in order to do that you are going to have to do something a little different,” he suggested.

Nutritional boost Agrii technical advisor David Felce briefly highlighted on-going trials work at Stow Longa looking at the role that nutrition can play in boosting later drilled wheat. He said that because later drilled wheat has a shorter growing period, nutrition in the seedbed in the form of a seed dressing could boost crop growth and, in turn, its competitiveness against black-grass as it establishes. “When you are drilling late on heavy soils everything has to be focused on a good seedbed and good soil structure – including the right balance of air and water in the soil to encourage biological activity – as well as maximising the use of fertiliser to supply the crop with the major nutrients,” he concluded. ■

Cultivation conundrums In the same project, different cultivation techniques were studied for their affect on black-grass control with a rotational plough demonstrating high levels of blackgrass control compared with direct drilling and disc- and tine-based cultivations. Interestingly, in year 3 (2012), direct drilling – following direct drilling in 2011 and min-till in 2010 – resulted in only 33 per cent control of black-grass with resulting wheat yields of 3.65t/ha.

Agrii adviser David Felce said that often there is negativity surrounding the use of the plough, but he suggested that it had delivered good results at Stow Longa this season and is a good method of injecting air into the soil to increase biological activity.

12 www.farmersguide.co.uk August 2017

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