Could weeds be controlled by zapping them? Extension is investigating

CORVALLIS, Ore. – In agriculture weeds have a huge impact on crops and the bottom line, especially on organic farms where using herbicides aren’t an option.

“Weeds are very problematic,” said Marcelo Moretti, weed specialist for the Oregon State University Extension Service. “Every commodity crop I work with that has an organic system lists weeds as their No. 1 research priority.”

So, in the spring of 2021, Moretti started a research project to determine the effectiveness of using electricity to control weeds. The method is not new – the first patent in the U.S was granted in 1890 – but the system required too much energy to be effective then. Now, scientists and equipment manufacturers are taking another look.

Moretti will lead a three-year, $2-million electric weed control study funded by the U.S. Department of Agriculture Organic Research and Education Initiative, working in collaboration with Cornell University and the University of California, Davis.

As weeds develop resistance to herbicides the cost of control rises and along with it, farmers’ frustration. As organic production increases in the United States and Europe, non-chemical control becomes more essential.

“It’s not a stretch to say herbicide resistance is a serious problem, not only in organic production but also in conventionally grown ag crops,” Moretti said. “Because of that, interest in electric weed control is rising. There are now companies making electric weeding equipment protypes. We’ve reached out to those companies to use their equipment.”

Electricity is a thermal weed control, Moretti said. The electricity is applied directly to the plant and once it gets inside, travels to the roots and comes out through the soil, it effectively kills the plants. The electricity is applied with electrodes connected to a tractor, which is run by a large generator coupled with a transformer. For Moretti’s study, he’s using 30 kilovolts-ampere and between 5,000 to 12,000 volts, significantly more than a household system. The method requires at least a 75-horsepower tractor, which most growers already own.

“We’re seeing better results than we expected,” Moretti said. “Most other non-chemical methods are not as efficient. We’ve determined that it has really good efficacy with the tractor moving at a mile and a half mph to kill ryegrass. The question now is should I go that slow in one pass or go through twice at a faster speed, which would kill weeds that were missed or re-emerging weeds.”

So far, there’s been excellent efficacy against serious perennial weeds like field bindweed, yellow nutsedge, Canada thistle and horsetail. Annual seedlings are easily killed. Himalayan blackberry has so much woody material it’s difficult to destroy, but electricity will knock it down for easier removal. Smaller weeds are easier to erradicate. The process can be used after a rain, though the more moisture in the soil, the more input of electricity is necessary. Saturated soils can be problematic, Moretti said, so judicious timing is recommended.

Moretti’s work concentrates on weeds in hazelnut orchards. Oregon produces about 99% of the U.S. domestic hazelnut crop. To date, Italian ryegrass is resistant to at least four herbicides commonly used in hazelnuts and control options are limited since tillage can’t be used.

“Soil tillage for weed control is alright, but you cannot do tillage in hazelnuts,” Moretti said. “If you disturb the soil, it will affect the harvest process and the tree’s roots and promote erosion. Tillage has side effects. You’re losing soil health as you till and breaking up the structure of the soil. That’s bad news for plant nutrition. Tilling may have a negative impact on plant growth.”

Because of that, growers are forced to use more herbicides, which is expensive. Mowing is an option but some weeds like ryegrass are not killed by mowing. Instead, Moretti is applying electricity to weeds in orchards to determine how safe it is among hazelnuts. For two years, he will measure how well the trees grow when electricity is used for weed control.

There are possible drawbacks to using electricity to control weeds, Moretti said, including human safety and fire. Correct timing will take care of fire and training will solve the human safety issue.

The cost is dependent on how fast the tractor moves. If It’s driven at 2 mph, the cost is less than $40 an acre, which is comparable to herbicide applications, but it will treat a smaller portion of the field.

“If what we’re seeing is correct, we now have a cost-effective non-chemical way to control weeds,” Moretti said. “We didn’t have one until now. Everyone recommends using non-chemical methods on resistant plants. It looks like we found something that’s a game-changer.”

Zasso, created in Brazil by a Japanese immigrant, is the furthest along at creating a prototype and was ready to share one with Moretti and his team when COVID-19 delayed things. So, in January Moretti and his team assembled the system themselves and by March it was fully functional in the field, which was good timing for controlling weeds. Summers are too dry and there’s concern about fires with electricity. If you kill weeds late in the season, they are already dying and it becomes meaningless to use electricity.

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