When Dr Craig Stewart started looking into the challenges farmers have killing weeds with herbicides, he wondered why this wasn’t a bigger deal in society.

“Everyone has to eat,” Dr Stewart says. “So it’s very important, given the increasing concerns about environmental contamination, environmental degradation and understanding how we're preparing that food.”

That’s why his PhD research with the ANU Research School of Chemistry explored how to produce new types of weed-killing plants derived from natural products, called bio-herbicides.

“I think part of what got me very interested in this project from the start, was that everybody knows about antibiotic resistance: you hear about it in every chemistry course.

“But then I started doing a bit of reading on herbicide resistance in agriculture. I thought, why aren’t people talking about this more?” Dr Stewart says.

The main herbicides used in agriculture have changed very little since glyphosate-based herbicides, such as RoundUp, became popular. Now weeds are becoming resistant to these really common herbicides. As they are less effective, farmers need to use more chemicals to get results.

“I think everyone thought glyphosate was going to be un-killable,” he says. “And then it was extremely fallible.”

“Especially, as we’ve seen in the last few years, there’s a lot of pushback against glyphosate specifically, because of all the long term health usage concerns.”

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Dr Craig Stewart. Photo: Nic Vevers/ANU

Dr Stewart’s task as a synthetic chemist was to develop molecules that could be used to produce more natural herbicides, with a commercial goal from the outset.

“We wanted to try to make a new product, however long that was going to take, because development is such a long timescale.”

The idea was inspired by the specific natural product, m-tyrosine, a non-proteinogenic amino acid found in a particular species of grass.

“This grass, called Festuca, produces m-tyrosine from its roots, and that allows it to combat its own environment,” he explains.

“In the presence of m-tyrosine, seedlings display stunted development, particularly of the primary root, ultimately leading to their death.

“It's actually used to line highways in the US because it prevents weed growth over the highways,” he says.

“These plants have been used for decades. It’s so effective. So there's something about that gradual release in that environment that works. It's also helping to really slow resistance development.”

This Goldilocks product would then be genetically engineered into crop plants which, once mature, would automatically prevent weeds from growing around them, without the need for spraying.

This model has worked previously for killing pests, but hasn’t yet being used in weed control.

“That will be really, really cool to be able to deliver a herbicide-producing crop that can protect itself,” he says.

Dr Stewart’s research got the ball rolling by developing a library of these bioactive molecules, but because of the extensive development pipeline there’s a still a long way to go before these bio-herbicides will be used on the farm.

“I was pretty sure at the start of the project that I wasn't going to see the end of it,” he says.

“The most important part is the journey. Everything that you learn in the process, by really getting invested in it, that's the real benefit.

“It's a process of investigation and surprise," he says.

"You end up with a weird, complex mixture from your reaction, so you're always putting together the clues on the chalkboard. It's kind of like being a detective every day.”

The answer to the problem of herbicide resistance, is that there is not one single answer, says Dr Stewart.

“I think a holistic approach with a real focus on a collection of techniques would be the best place to go. Obviously, I'm not a farmer, I’m a chemist, but there are lots of non-chemical methods which aid in delaying or preventing the development of resistance in particular crops or fields,” he adds.

“A big part of the reason why we're in this bind right now, globally, with this complete lack of novel herbicides is because people refused to bring in additional weed control techniques outside of synthetic herbicides.”

We need researchers like Dr Stewart to change that.

“Having gone through that PhD, you can come out at the end saying: I can address all these problems, I have the skills.”

If you’d like to help new products take root, consider a Bachelor of Science, and PhD in Chemistry.