Improving soil hygiene to minimise the spread of weed seeds could help tackle grass-weeds, and good practice is backed up by some interesting equipment overseas. Jane Carley finds out more.
In the battle to gain control over arable weeds, growers are increasingly looking to their entire farming system for clues on how to reduce weed seed populations. Black-grass, in particular, is being reported in parts of the country where it has previously been unknown and one cause of its spread may be seeds being transported to those areas from more traditionally afflicted areas.
Weeds can quickly spread to previously clean fields and, if herbicide resistance is present, control can become challenging.
Richard Hull, weeds ecology and evolution technician at Rothamsted Research, says: “It is vital to know which are your worst fields for weeds, and also the distribution in those fields. If resistance to herbicides is present in those weed populations, it is imperative to stop seed spread to other parts of the farm for long-term sustainability. The effectiveness of any measure to stop seed spreading is dependent on many factors, including population size, time and implementation.
“If possible, clean machinery between fields. It is time consuming but could pay off in the long run. Cultivate the worst fields last, therefore not dragging seed to cleaner fields. Ideally, enter and start cultivating from cleaner parts off a field, finishing in the worst areas.”
The most important action, he maintains, is not to spread seed any further than its current limits.
Another possible cause of weed seed spread is from the combine, especially in the chaff, Mr Hull points out.
“Where possible, make sure all chaff is removed from the combine before moving to the next field, although again, this has time implications.
“Another option where time is at a premium would be to start in the worst part of the field and finish in the cleanest. This way, seed would be spread in the field, but finishing where the weed burden is lowest should ensure the lowest level of carry over to the next field.”
Soil hygiene is also at risk when using contractors, he says.
“If you have contracted a combine to come and harvest land, make sure the machinery has been fully cleaned out before arriving on your farm. The last thing you want is weed seed, which could have resistance issues, being spread on your land.
“The same could be for said for balers and the movement of straw. This movement of machinery could be one of the main reasons certain weed species appear to be moving into areas of the UK where they have not been seen much before.”
In mainland Europe, chaff management is being developed as a solution to weed seed spread. French manufacturer Thierart specialises in chaff management solutions, from swathing systems to collection hoppers which can subsequently be emptied into heaps away from the harvested area. Collected chaff can be stockpiled or baled and then turned into biofuel pellets or briquettes, or used as animal bedding or a feed constituent.
The company claims chaff recovery can decrease weed populations by 97%, reduce the incidence of diseases, such as fusarium, and cut slug populations, minimising the need for treatments and offering savings of up to €35/hectare (£24/ha).
Cereal crops yield up to 2.3t/ha of chaff which is used as a biofuel feedstock across France, with barley grown in the Loire Atlantique region offering biogas potential of up to 263nl/kg from raw material.
When baled in with straw, it offers from 0.7-2t/ha of extra bedding material, with an increased absorption capacity and low dust content, said to be ideal for poultry. Trials are ongoing with poultry producers Moulin Henry and Doux as well as cattle breeders the Meusienne Union Dairy.
It is also used as a fibre feed for improved digestion in cattle fed on starch-rich diets.
As a heating material for pelleting or briquetting, wheat chaff offers energy yields of 15,240kJ/kg – more than two-year old hornbeam wood at 12,560kJ/kg.
Thierart’s chaff collector models are available for most makes and models of combine and weigh 800-1,100kg. The chaff collector is fitted to the rear axle of the combine and supported on the grain tank. A mechanical screw auger loads chaff from the rear of the combine to the hopper, which is emptied hydraulically. The unit is priced at €30,000-€40,000 (£21,000-£28,000) depending on model.
Also in the range is a two-stage turbine designed to remove chaff from the combine, optimising material flow and reducing risk of jams. The company says this is a good solution for smaller combine harvesters equipped with cutter bars smaller than 5.5 metres; options include removing the chaff in a trailer or windrowing it via a deflector. A chaff chute also allows chaff to be spread or placed on top of the straw.
Thierart’s tractor-mounted collector system can blow tipped windrowed chaff either into a trailer or into the pre-chamber of a baler, using a paddle to collect the chaff to prevent any backflow of earth or stones.
A different approach is offered by the Harrington Seed Destructor, developed by farmer Ray Harrington, Western Australia, with assistance from the Grains Research and Development Corporation (GDRC).
The original design features a diesel-engined trailed mill, based on a processor used in the mining industry. It collects chaff from the rear of the sieves and crushes seeds before blowing the residue out on top of the straw swath. Combine cutter bar heights need to be slightly lower in most crops (described by Mr Harrington as ‘beer can height’) to ensure most weed seed heads are processed.
Field trials have shown up to 95% weed seed destruction efficiency when used during commercial harvesting of wheat, barley and lupins.
A new version of the machine has since been developed to process chaff as it exits the header of class 9 and 10 combines, enabling straw to flow into the spreader. The integrated approach, which mounts the mills on the back of the header, is designed to use less power and have a higher capacity than the original version. It is still being evaluated by the GDRC ahead of a commercial launch.
Despite using the header’s power system, the new version processes chaff at more than 30t/hr, spreading the crushed mixture evenly across the field. The commercial tow-behind HSD is still used for class 6, 7 and 8 headers which do not have enough power to drive the integrated mills. It is manufactured and marketed by De Bruin Engineering, of Mount Gambier, South Australia.
Mr Hull says: “This device is mainly used to tackle rigid rye-grass in Australia, which comes to inflorescence later than black-grass and more seed is on the plant at harvest. By the time winter wheat is harvested in the UK, about 99% of all black-grass seeds have shed.
“However, it may have an application in winter barley, where up to 30 per cent of black-grass seed could still be on inflorescence at harvest. It could add a further non-chemical weed control option for growers who have ALS-resistant black-grass on their farms. The same chemistry can be used on barley as in wheat crops, but it is more competitive to weeds.”