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A new way to control weeds. Zap them

Weeds like these that dried out in a median along Santa Fe’s St. Michael’s Drive in 2018 possibly could be controlled using electricity if research at New Mexico State University’s College of Agricultural, Consumer and Environmental Sciences pans out. Santa Fe city government has launched a ‘war on weeds.’ (Eddie Moore/Albuquerque Journal)

LAS CRUCES – A researcher in New Mexico State University’s College of Agricultural, Consumer and Environmental Sciences (ACES) is leading efforts to understand the biology of what’s happening inside weeds and trees as electricity is being used to safely and effectively kill them.

Erik Lehnhoff, assistant professor of weed ecology in the Department of Entomology, Plant Pathology and Weed Science, and his team have received a competitive grant of $45,115 from the college to collect background data and write a proposal on how electricity can control weeds.

Lehnhaff’s team includes Paul Neher, a local inventor and hobby farmer; Donovan Bailey, a professor of biology; Wayne Van Voorhies, a molecular biologist; and Leslie Beck, an extension weed specialist.

The researchers are working on two different systems, a tree-killing operation and a weed-killing operation. Both work on the principal of running an electric current through the plants and into the ground through a continuous loop.

“It’s a very low current, less than an electric fence, so you can get shocked a little. It’s not pleasant, but it won’t harm or kill you,” Lehnhoff said. “For trees, we put a screw into the tree near the root crown and attach the lead to it and it runs electricity through the tree and down to the roots. Over the course of a couple of days, it will end up killing the tree. It does depend on the diameter of the tree, so bigger ones will take longer.”

The system has been tested on nuisance trees like Siberian elm or Mulberry that can grow through landscapes where they’re unwanted.

Cutting the trees off at the surface often doesn’t kill these invaders because they regrow from the roots. If they are dug out, it makes a mess and other desirable plants can be ruined. If herbicides are used, there’s a risk of accidentally killing nearby plants.

When it comes to killing herbaceous weeds, a quarter-inch screen mesh is placed on the ground to carry an electric current.

“The screen almost acts like a pre-emergent herbicide,” Lehnhoff said. “When weeds contact the screen, there will be a low current of electricity going through them and preventing them from growing. This will be a great application for a landscape where you have a few ornamental plants and don’t want anything anywhere else. We’d cut out a hole for the size of plant you want to keep and have the electric mesh everywhere else.”

This operation has been used to kill Bermuda grass, which spreads above and below the ground, and is very difficult to remove. The mesh screen is laid on the spot of grass to be removed and hooked up the electricity. Over several days, the grass will be killed.

Researchers believe the current is going down to the roots and inhibiting plant growth. Plants not contacted initially by the screen eventually emerge, connect with the screen and are ultimately killed.

Lehnhoff explained that there have been similar systems in the past, but they used very high voltage that ended up boiling the plants. That option wasn’t safe and didn’t always kill trees targeted for removal.

“In terms of how it works, we still don’t really know,” Lehnhoff said. “There are a lot of electro-chemical processes going on in plants at the cellular level and with transports of solutes through the plants.

“So, it could be something as simple as disrupting water and nutrient uptake into the plant or it could affect photosynthesis and the movement of ions across cell walls. Those are the types of things we are still working on.”

Neher, an electrical engineer, developed the electrical plant control idea. He wanted to kill weeds at his own house and on his few acres of pecan trees without using herbicides.

“He started playing around with this idea of electricity and ended up discovering a certain signal that could be used to kill weeds,” Lehnhoff said.

Lehnhoff said the method the NMSU group is working on could be used mostly for landscaping. There is still research that needs to be done to see how to apply similar methods to larger scale farming because irrigation presents a problem when trying to use electricity to manage weeds.

“This could be a tool that replaces some herbicide use because a lot of people don’t want to use herbicides any more. Also, this method would be great for someone with an organic garden,” Lehnhoff said. “It can also replace the plastic weed barrier that is placed under landscapes to minimize weeds from coming up.”

Lehnhoff and his team are currently running tests to understand what’s going on within the plants as electricity runs through them. They are establishing sample plants that will have different levels of exposure to electricity. Plant tissues will be collected and gene expression will be analyzed in an attempt to determine which plant pathways are being affected.

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