Ongoing restrictions to the availability of herbicide actives means alternatives may soon be needed. Jane Carley takes a look at developments in electrical weeding.
Harnessing electricity to destroy weeds is not especially new, but the challenge has always been how to make the technique viable for field-scale work.
From tractor-mounted solutions to robots, several manufacturers are looking into the technology including CNH Industrial (parent company of Case IH and New Holland), Lemken, The Small Robot Company and Rootwave.
First announced at Agritechnica 2017 and now in commercial production, the Xpower tractor-mounted electrical weeder is part of the AgXtend suite of precision farming equipment from CNH Industrial.
Xpower’s high-voltage electricity is provided by a generator mounted at the rear of the tractor, with electricity transferred to the front-linkage weed destruction unit. Sensors and/or a camera-based guidance system is used to steer the machine, with control over the tractor taken care of via Class 3 IsoBus system.
A series of paddles pass over the ground and when one paddle makes contact with the weed leaves, an electrical charge travels down through the plant to the soil. Another paddle touching an adjacent weed closes the electrical circuit which conducts electricity through the plant, destroying its vascular bodies and causing it to ‘wilt’, although treated weeds can initially appear moist as water is carried out of the plant.
In common with many new developments, this year’s trials have been hampered by the pandemic, but the three-metre working width tractor-mounted electrical weeder saw action in October with selected salad, vegetable and cereal growers in the UK.
John Downes, CNH Industrial precision farming manager, explains: “We trialled the Xpower with a salad grower who wants to control glyphosate-resistant nettles in lettuce post-harvest.
“The nettles form a ‘carpet’ which cannot be controlled with glyphosate and the only other suitable product has recently been withdrawn. The trial was carried out with passes at 1.5, 2, 3 and 6kph and while we saw the best results at 1.5kph, control was also good at 3kph – significant since the existing method of non-chemical control is to use a gas burner which travels at 1.2kph. Data from the trial will be used in a wider NIAB/AHDB study so it will be interesting to see the conclusions.”
Mr Downes says there is also interest for controlling oilseed rape volunteers, but away from the high value vegetable/salad sectors where there are few chemical alternatives, potential is limited by work rates. While other configurations are being explored, 3m is believed to be the best starting point for field-scale crops. There is also the potential for section control for use where weed burdens are less.
Conditions affect the speed of the operation, with a dry day being the most favourable for connectivity, while fresh, moist growth is more easily killed than mature plants. Regrowth time depends on the root mass of the weed.
For safety, the unit monitors waveforms so will pick up obstructions or unintended targets and turn off the connectivity, while a rubber skirt will prevent anything getting under the unit. But with the generator producing 2,000 volts, the operator is required to test all paddles with a volt meter at the end of the process to ensure they are no longer active before allowing anyone else to approach the machine.
Impact on soil microbiology was found in German trials to be little different to chemical applications and there is said to be no long-term effect on soil fertility. And, of course, no residue, says Mr Downes.
“It is not in itself a new technique – several electrical weed control devices were developed at the turn of the 20th century, but as herbicides became available in the 1930s, they died out.”
There will be two other production models on the market in 2021. A 1.2m front-mounted unit for use on a compact tractor in amenity weed control applications and a vineyard-specific variant with two or three applicators on break-back arms with rubber flaps to protect the vines.
Prototypes include an inter-row version for use in crops, with the crop protected from the conductors by ‘hoods’ similar to those on a shielded sprayer. CNH Industrial is also looking at applications for use as a desiccant in potatoes – an increasing interest now diquat is off the market.
“The challenge is that the kill rate and effect on the tubers depends on the variety and time of year,” says Mr Downes.
“We need to be able to destroy the tops without damaging the crop. We are also exploring how this type of desiccation will affect skin set.”
Recognising this is emerging technology that will continue to develop, CNH Industrial is offering customers the opportunity to lease the XPower from periods of two weeks upwards.
“We want them to be able to experience the effects without having to invest £160,000 in a machine that is likely to change. We can take a lease machine back in and upgrade it – we have already seen that the latest design uses 30 per cent less power than the 2019 model which is out with farmers, but with the same effect at 30 per cent lower cost.”
Small Robot Company is developing weed ‘zapping’ technology for its Dick robot and, after in-house field trials earlier this year, has progressed to farm trials with its farmer investors this autumn.
Chief marketing officer Sarra Mander explains: “Using weed maps from data gathered by the Tom robot and processed using artificial intelligence, five probes on the Dick robot destroy weeds with an electrical charge that passes down the stem and into the root, using a soil engaging wheel to complete the circuit.”
The technology is already proven in partner Rootwave’s handheld electrical weeders which are used in the groundcare industry, but lower voltages are required to tackle relatively soft, leafy weed growth rather than the likes of Japanese Knotweed, for example.
Weed mapping will also permit selective weed control, where farmers may want to leave favourable non-crop plants, such as pollinators, undisturbed.
“Establishing weed thresholds helps increase the efficiency of the weeding operation while also impacting on pricing,” Ms Mander adds.
“Some farms may have a maximum price for weed control of £150 per hectare and a ‘zero tolerance’ approach will be more costly. Equally it may be necessary where the aim is to control yield-limiting weeds such as black-grass.”
A commercial weed zapping service is expected to be launched in 2021, alongside a satellite office in Cambridgeshire to extend the scope of field trials.
Lemken bought Dutch manufacturer Steketee, best known for its mechanical weeders, in 2018, intending to develop its products to offer a range of non-chemical weed control solutions. This includes the use of electrical weed destruction and discussions have taken place with Rootwave in the UK to supply the electrical solution. Steketee has already advanced into automatic camera guided mechanical weeding.
This summer, Lemken also announced it was pulling out of crop sprayer production and moving its focus to non-chemical weed control.
Laurens Struik, designer at Steketee, says: “The Lemken Group is still involved in ongoing projects looking at electronic weeding and we believe such innovative methods and technology will be at the forefront of agricultural crop care in the near future.”