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A “Death-Ray” for Weeds Could Replace Chemical Weed Killers

Don't lie, gardeners. Bent over like a cooked shrimp, pulling weed after weed from your garden, you've thought to yourself, I wish they were all dead.

Spraying weed killer near your prized plants can be tricky, but picture this: a weed, sucking up valuable sun and nutrients — but suddenly, a shadow passes above, and deep within the plant pest, tiny, violent vibrations begin. The molecules shake, the water inside warms and expands, until its cell walls come down like Jericho — and the weed is destroyed.

Dr. Graham Brodie of the University of Melbourne is working on a method that could make this very satisfying fantasy come true: a device for zapping the stubborn plants with microwaves.

"By using microwaves to heat the water particles within a weed, the vibrations cause the plant cell walls to explode, killing the plant," Brodie told the university's publication Pursuit.

Microwaves create electromagnetic fields that oscillate rapidly, causing polarity to flip back and forth extremely quickly. Heat is produced by the friction of the water molecules in the cell rapidly moving to try to match the polarity.

As herbicide resistance rises, non-chemical means of killing pests will become more and more crucial.

The microwaves can also destroy dormant seeds, using higher energy to push underground and essentially cooking them before they can germinate. Although this has a harmful effect on the biomass of the soil, the bacteria seem to bounce back quickly, Brodie says.

The challenge was in delivering the microwaves effectively and accurately across a broad area, while also being energy efficient. Brodie has created an antenna system that can focus the microwaves directly at the weeds or strafe under the soil, for a pre-emptive strike.

Placed on a trailer, it can be drawn behind a tractor to kill weeds across an entire field, without the need for herbicides. (It's conceptually similar, if less wasteful and destructive, than the propane flamethrowers some organic farmers are using to kill weeds.)

"By using microwaves to heat the water particles within a weed, the vibrations cause the plant cell walls to explode, killing the plant."

Dr. Graham Brodie The University of Melbourne

As herbicide resistance rises, non-chemical means of killing the plant pests will become more and more crucial. Much in the same way that a few bacteria develop resistance to antibiotics and become "superbugs," plants that survive an herbicide can produce a legion of seeds that grow to be herbicide-resistant super-weeds.

The problem is a big one: the International Survey of Herbicide Resistant Weeds shows 164 varieties identified in the U.S. alone. Resistant pigweed is so common in parts of Minnesota and Arkansas, Scientific American says, that farmers have begun hiring workers to rip out or blowtorch them.

Even worse, some weeds are showing resistance to multiple herbicides, which work in different ways. This means that simply utilizing a different herbicide — or even a rotating cast of them — may not be enough to hold off resistance.

That resistance may cost farmers millions of dollars annually.

Resistant pigweed is so common that farmers have begun hiring workers to blowtorch them.

Non-chemical methods of plant control can be used for environmental measures as well as agricultural. In 2017, a pilot program in Lake Tahoe used UV rays to kill invasive plant species.

Experts at the Department of Agriculture warn that herbicides may eventually become obsolete; the race is on to find ways to kill weeds that do not rely on their application. And doesn't blasting microwave radiation across the fields like an alien overlord seem like a pretty great method to do so?

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