As the pressure on chemical weed control continues to grow from multiple sources – whether from resistance development and active ingredient withdrawals to water company issues and consumer demands – mechanical methods of controlling weeds are attracting closer attention from growers of combinable crops.
But while inter-row weeding early in the season on wide-row, band-sown cereals is one thing, controlling grass-weeds later in the year is quite another.
The experiences of one Suffolk large-scale organic farm, though, suggest above-crop grass-weed control shows promise.
John Pawsey’s Shimpling Park Farm, Bury St Edmunds, Suffolk, began organic conversion in 1999 and completed the process in 2007.
The farm comprises 650 hectares of mostly Hanslope clays, with a further 980ha of contract organic farming.
A flock of 1,000 New Zealand Romney sheep grazes 500ha of two-year grass/ clover leys, while the 1,200ha of all-combinable cropping is grown for specific end-users, with wheat and beans going to animal feed mills.
Barley is normally sold as malting and exported to the continent; oats are grown for White Oats, spelt goes to Sharpham Park and the farm’s quinoa crop is bought by the British Quinoa Company.
All grain marketing is done by Andrew Trump of Organic Arable.
Since the beginning of conversion to organic production, routine mechanical removal has been central to weed management, with several different machines used in sequence, depending on crop and growth stage.
Only relatively recently, however, has tackling grass weeds been successful to a significant extent late in the season, thanks to investment in a French-made machine first seen by Mr Pawsey at a farm show in France in 2015.
He says: “We’ve been gradually moving away from the plough to minimum tillage and one of our most successful weed management tools has been the CTM Weed Surfer, which is a great machine, one on which we provided some development feedback.
“The key issue though is with weed stage and size in that once its hood is over the top of the crop the blade downdraft can push the weeds around.
As a result, we would sometimes have to make further passes to catch missed weeds.
“When in France in 2015, I saw the Bionalan Selac, which uses a slightly different but still very simple principle.
“Built around an intermediate chassis cushioned by a nitrogen ball cylinder and with a central pivot, the machine features pto- or hydraulically-powered rotating blades working against fingers to decapitate grass-weed seed heads above the crop before the seeds reach maturity. As a result, they do not germinate and create new plants.”
Each blade covers a metre of the machine, which is available in 4m/6m/9m/12m models.
Working height of 0.15-1.8m according to crop is set via a mast and angle can be altered hydraulically, while front or rear mounting is possible.
Dividers are height-ad justable to adapt to crop and weed height and, with its open structure, there is no wind from blade rotation to affect the weed stand.
Impressed by the machine, Mr Pawsey found there was no UK importer and, after considering bringing one in himself, finally did so in time for spring 2022.
Since then, an agent has been appointed.
“Our main grass-weed issue is wild oats and I’ve done lots of research over the years collecting seed samples at different stages and sending them to NIAB to determine viability.
“It’s not an exact science, but once the plant is flowering halfway up the panicle you have about a week to 10 days to cut before the seeds at the top become viable.
“Oats are very pernicious and it takes relatively little seed return to quickly result in an infestation that smothers crops.
“One of the first fields we con verted to organic production was a sea of wild oats and through use of the CTM machine and agronomic advice we have pretty much now got it to a rogueable state.
“The natural next step was to find a tool that could give us similar results in fewer passes and that led me to the Bionalan Selac.
” When first using the Selac, Mr Pawsey found it relatively easy to set the machine to just skim the crop surface.
“However, we found that height precision is really important, as this skimming is just enough to cause light damage that can subsequently allow development of ear disease and we were seeing low levels of bunt.
Uneven fields can also cause uneven work, but we’re doing very little ploughing now and our fields are more level as a result.
” Forward speed depends on the infestation, but is usually 8-10kph with his front-mounted machine, adds Mr Pawsey.
“With an experienced operator it’s possible to do quite a lot in a day, but they need to be focused on machine height, especially where land is uneven, so it can be demanding to operate.”
The Selac proved effective on wild oats during its first season and in addition worked well in tackling charlock, another of the farm’s key weeds, says Mr Pawsey.
“To tackle that we used the machine earlier, pre-flag leaf of the crop.
It’s helped get charlock in hand on our handful of problem fields.
“We didn’t have it early enough to use the Selac for black-grass control, but it’s something we will try next year, although it’s not such a key weed for us as our broad rotation helps suppress it.
But where it does occur it’s a challenge for mechanical control as it’s such a spindly, light plant.”
Mr Pawsey’s crop establishment is based around a pair of System Cameleon low disturbance drills imported from Swedish maker Gothia Redskap.
With units shifted over and coulters changed, the machine can also be used post-drilling for initial weed control via inter-row hoeing, as well as undersowing where required.
Wheats are sown at around 350 seeds/sq.m, depend ing on thousand grain weight, to aid early weed suppression.
“Over the past 20 years we’ve learned a lot about weeding at various stages of various combinable crops and, coupled with our drill hoes and tined weeders, I think we’ve now honed the machinery fleet to what we need.
The next thing we may look at is the value of variable rate seeding to up rates and outcompete weeds where there are known patches.”
Winter crop establishment now relies largely upon a Farmet Fantom deep tine unit followed by one of a pair of Farmet Verso 8 spring tine cultivators or a Vaderstad Carrier 925 short disc, depending on conditions.
The Cameleon drills then look after sowing and early inter-row weeding.
Spring crop land is ploughed or increasingly, min-tilled where possible, with a target to minimise fuel use.
“The first spring with the Selac appears to be helping us in getting towards the levels of weed control I’ve been seeking since we moved to organic production,” says Mr Pawsey.
“It fits into a weed control system that also includes the Cameleon drills and a Weedcut ter Combcut, also made by Lyckegard and also imported by Primewest.
The latter is an even more recent arrival, and is reckoned effective in destroying thistles, nettles, charlock, docks and black-grass.
I purchased one after seeing what it could do and am looking forward to working it alongside the Bionalan machine this coming season.”L