For more than a century, agronomists have entertained the idea of shocking weeds into submission using electricity. The first patent for the tech was issued in the 1890s for electric weed killers, large, lethal monstrosities as dangerous to their operators as to the weeds targeted.
But work by Massey University PhD student Dan Bloomer in conjunction with Professor Kerry Harrington of Massey has proven weed control using very small doses of electricity is possible and safe across a wide range of weed types found in New Zealand crops and pastures.
Bloomer’s work fits under AgResearch’s wider project investigating weed resistance in NZ, a problem lead scientist Trevor James says is increasing at a rate beyond expectations.
“We have been doing surveys for four years and have found resistance as high as 45% in Waikato maize crops, while the number of weeds showing resistance has increased 50% in four years to 19, that we know of,” he says.
James says the resistance level surprised even seasoned experts like himself who expected to detect only about 5% resistance.
After a lull in electric shock treatment for weeds there was a surge in interest through the 1970s and ’80s. However, the launch of glyphosate saw interest subside as weed wiper methods were taken up.
The use of electricity has continued in places around the world, including organic operations, but Bloomer says the energy intensity of the equipment is high, and there is still operator risk.
Working with custom technology akin to electric fence energisers, Bloomer trialled high-voltage, low-energy equipment that uses less than 1% of the energy other technology consumes.
“If you were to look at the energy consumed in diesel terms, microwave technology uses about 2000 litres a hectare, steam and flame about 200 litres, ploughing 5-30 litres, herbicide 20 litres, and this machine about 30 millilitres a hectare.”
The machine – which is subject to its developer’s IP – can deliver a low level of electric current at a pulse rate of microseconds to targeted weeds.
“It is similar energy levels to an electric fence but multiple times a second. It will jolt you, like an electric fence, but it is not as dangerous as if you were shocked by household mains,” says Bloomer.
The conventional electric weeding approach essentially boils the plant’s tissue, bursting the cells. Bloomer’s method doesn’t appear to work the same way, though he is still researching possible mechanisms.
It has proved effective on seedlings of wireweed, fat hen, redroot, black nightshade, common speedwell, shepherd’s purse and thistles.
Grasses could prove problematic, with a need to get more energy lower down into the base to hit them in the growing zone, rather than just the leaf. Hitting the grasses before they are tillered appears to be most effective.
“With enough power you can kill anything. But you need to be able to do it with a low level of power, that’s the trick.”
Treatment time amounts to fractions of a second, with more time spent moving between weeds than on them.
Bloomer says he can see the potential for the kit to be used in robotic technology. He says it is a contrast to much of the tech developed now that involves attaching age-old methods like sprayers or cultivators to robotic machines.
“The reality is a robot would consume more power moving between weeds than the zapper itself.”
James says there are two reasons Bloomer’s machine has potential.
“It is ground based, and not weather dependent and can be attached to robots that can operate at night, giving it a very wide range of operability.”
The machine’s low level of energy consumption and safety add to its usability and ability to be adapted to a wide range of weed control applications. It could include having a rechargeable handset not dissimilar to an electric drill in configuration.
“What we like about it is the ability to use it when scouting for resistant weed populations. I have visited farmers doing enormous amounts of work to get rid of resistant weeds, digging up large areas of arable land at great cost and loss.”
Vineyards have been an early source of resistant weed development and are limited in their ability to use herbicides.
“This sort of technology would mean they can extend their use of herbicides and control the weeds,” says James.
He says the electric tech is one of a portfolio of options being studied under AgResearch’s resistance programme. Other projects include more work on microwave use, virtual paddocks to control stock access to weed-infested areas, bio-controls for weeds and RNA-altering technology.
