Stem Shock: new herbicide in development

A new mode of action based on RNA could soon be killing a weed near you

Palmer amaranth.

It’s been over 20 years since chemical companies released a new mode of action in herbicides. But a B.C.-based company is cooking up a whole new type of herbicide.

“We use a different mode of action for the actual killing of the plants than a lot of traditional herbicides. Most herbicides, by reducing the specific level of proteins, will starve the plant,” says Chris Tuttle, co-founder of Cotyledon Consulting.

Cotyledon’s new weed killer, dubbed Stem Shock, contains RNA, a molecule that carries protein-regulating instructions from a plant’s DNA. The RNA in Stem Shock will reduce the amount of protein the weed produces, killing it, Tuttle explains.

Tuttle holds a biology degree from the University of Victoria, and along with co-founder Layne Woodfin, forms the scientific team for the company. Sam Mercer works full time on business development for Cotelydon Consulting.

Stem Shock is designed to work on a specific weed species. “You would need a more or less perfect match between our RNA and the RNA present in the weed for those genes. And we have to target multiple genes to have an effect.” They target regions of a plant’s gene that varies quite a bit between species, to make sure they’re not hitting off-target plants.

Targeting multiple genes will help slow resistance to Stem Shock, Tuttle says.

“But more importantly, weeds can’t develop resistance to RNA interference itself without compromising most of their immune systems, because they use it for so many other things. So they can’t develop resistance in traditional ways. All they can do is alter the sequence of the genes that we’re targeting so that our RNA doesn’t perfectly match anymore. And so at that point, it’s easy enough to build a new RNA that’ll be effective again.”

Focus on ag weeds

Scotch broom, an invasive weed that plagues Tuttle’s hometown of Victoria, B.C., area, was a burr under Tuttle’s saddle that helped inspire Stem Shock’s creation.

“I’ve always wanted to have a solution to these invasive weeds that isn’t so destructive,” says Tuttle. Victoria isn’t the only community struggling with invasive weeds. Florida sprays herbicides in waterways to control water hyacinth, Tuttle says.

But as much as Tuttle would like to help municipalities control invasive weeds, the markets either seem too small, or it’s not clear how much money is being spent on invasive weed control.

“Whereas when you’re looking at agriculture, the numbers are clear, so it’s a lot easier for us to build a model around it.”

Tuttle says they’ve decided to focus on water hemp and Palmer amaranth because U.S. farmers face herbicide resistance in both those weeds.

“The plan will be to sell as a tank mix with glyphosate to farmers who are currently growing these Roundup Ready crops where they’re having the problems.”

One reason farmers face a herbicide-resistance “epidemic” with weeds like Palmer amaranth is that they’ve been reluctant to change, and many are still spraying glyphosate, she says.

“And it makes sense until the second or third year of a Palmer amaranth infestation, when suddenly your crop’s pretty devastated.”

Cotyledon Consulting has filed two patents with the World Intellectual Property Organization. They’ve lined up a manufacturer for the RNA itself. Once they’ve produced the RNA, there will be formulation, packaging, and distribution to organize. Tuttle says they plan to work with independent distributors in the U.S. facing herbicide resistance. They’ll place technical sales reps to get test commitments from farmers to see how Stem Shock works in the field.

Tuttle isn’t the least bit phased by the idea of targeting other weeds. Genetic sequencing is already available for some target weeds, or, they can map that information themselves for somewhere between $5,000 and $10,000. With that data, they can use their algorithms to build RNA molecules.

Creating these RNA sequences is “much, much easier” than developing the small molecules used in traditional herbicides, Tuttle says. Generating the RNA only takes a few months in the lab.

One big question is whether a product like Stem Shock will need to go through 10 years of regulatory testing for each RNA sequence, or whether Cotyledon Consulting will be able to get the entire mode of action approved.

The Environmental Protection Agency is developing protocols for regulating RNA pesticides, Tuttle says. “There are some interesting precedents being set, but it’s a much bigger question of regulatory than the actual technical capacity with these herbicides.”

But RNA is a food molecule, already being sold on Amazon as a nutritional supplement. That gives Tuttle hope that they could even get it approved by organic regulators.

Readers can reach Chris Tuttle by emailing [email protected].

About the author

Field Editor

Lisa Guenther

Lisa Guenther is field editor for Grainews based at Livelong, Sask. You can follow her on Twitter @LtoG.



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