Hot air, lasers, irradiation scrapped; researchers decide on electrocution

Unlike previous attempts at using electricity to destroy weeds, this method passes through the root and then the soil

Steel might not be the only way to kill weeds without chemicals.

“A decade or so ago we looked at high energy microwaves for weed control alternatives,” said Ken Greer of Western Ag in Saskatoon.

The agronomist has long sought out alternatives to conventional processes in prairie agriculture, including the company’s PRS Probes, which replace soil sampling for nutrient monitoring.

“Microwaves didn’t raise temperatures enough to kill the weeds, so that wasn’t going to work, but then I ran across Zasso’s efforts,” he said.

Greer spoke to the German company about the technology and found it had plans to commercialize and market it in North America.

“(Zasso) told me they were planning to look at the zero-till market in North America, so they were planning to take the idea to California agriculture,” Greer told a small room of veteran Saskatchewan equipment company engineers and officials.

“I told (Zasso) that the Prairies was actually where no-till lived and here they are.”

Matthias Eberius had a successful environmental testing background, using duckweed tissue to measure materials present in surface water.

Along with partner Dirk Vandenhirtz, he was seeking similar technology models that looked at doing “traditional processes in non-traditional ways.”

“Most development of new herbicides stopped 25 years ago. Glyphosate is in trouble in many countries. It is public perception, but it is real because of it,” he said.

“A new non-selective method of controlling weeds that didn’t involve chemicals is needed and we could see that opportunity.… We looked at hot air, lasers, irradiation, but these weren’t focused on the plants enough.”

Those tactics usually killed the tops of the plants.

“Lasers tended to pass through the leaves, burn holes, not kill them,” he said.

A Brazilian researcher had been working with farmers to kill weeds using high-tension electricity, and that caught the German scientists’ attentions.

“Tillage has been the traditional means if you want to kill without chemicals, and it avoids developing resistance,” said Eberius.

While the idea isn’t entirely new, patents for using electricity to kill plants in the fields go back to the 1950s.

“But the Brazilian work took it a step further,” he said.

“The soil is not the ground. The circuit is completed though the roots and then the soil. That is what kills the plant.”

Depending on the size of the plants and the soil conditions, this means passing 5,000 to 15,000 volts of pulsed electricity though plants at 2,500 to 15,000 Hertz. The pulsing minimizes the sparking effects of the high voltages.

The drier the plants and soils, the higher the voltage needed.

Testing for 10 years in Brazil with fields ranging from sugar cane, and its giant weed issues, to no-till bean fields has shown that the system effectively terminates weeds of all sorts.

Getting high-tension power safely into a weed was the challenge.

The Germans worked with their new Brazilian partners and investors from Switzerland to develop tractor power take-off driven generators with transformed high frequency, high voltage electricity that could flow from shoot to root and through the soil to close the circuit.

“We see almost no regrowth of the plants that are treated this way, and with no open soils, there is no erosion or issues related to tillage, no issues related to chemicals,” he said.

“So it is timely for the agricultural community.”

The Eletroherb’s mode of action is to instantly damage the plant’s chlorophyll and cell integrity from the leaves to the roots. Vascular bundles are broken, leading to very rapid drying down of the tissues after 100 to 1,000 joules of power are passed through the plant.

“It only raises the temperature a bit, so there is no cooking of the tissues or burning, raising temperatures 20 to 30 C,” he said.

Metal pads act as electrodes to carry the power to the plants, and these can cover a whole area or just work between rows, depending on the configuration.

In very dry conditions, a disc can receive the power.

“It is the most effective when power flows into one plant, through the soil and out through another plant, effectively hitting them twice, but it can flow through the plant into the soil and this works well, too,” he said.

Managing the power has been key in the development of the implements because electricity generation and handling typically don’t work well when demand rises and falls rapidly.

“We have solved that issue,” Eberius said.

“Depending on the conditions (of the plants and soil’s conductivity), the width of the machine, it will determine how fast you can travel in the field.”

The system doesn’t appear to affect microbial activity with stubble and plant tissues breaking down at similar rates to herbicide terminated weeds.

More research is needed to understand the effects on insects and worms.

It may be desirable for some pests to have control from the power system, but in others, such as earthworms, it might not.

“We will be looking at these issues beginning very soon,” he said.

The electricity in the system is focused on moving from the source and back to the circuit, so plants that are adjacent to the contacted weeds are not injured.

“You have to touch the plants to kill them,” he said.

“But it open up options for killing tall weeds in short crops,” and that would work in a prairie lentil field with volunteer canola or where kochia was taller than the legumes.

The company feels its tool would not replace the need for other types of weed control, such as chemicals in conventional crops and tillage for organics, but it would offer a cost effective alternative that would meet some market demands for chemical-free control and where herbicide resistant weeds have developed.

 

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