Scientists have demonstrated that they can use a crop spray to silence genes in plants, rendering the plants resistant to a virus for several weeks.

A team at the University of Queensland in Australia has developed a technique that allows it to deposit RNA onto the leaves of crops. The spray makes use of microscopic sheets of clay, into which RNA is loaded. As the sheets stick to the leaf of a plant and gradually break down, the RNA is taken up by the plants where it is processed and used to trigger silencing of the genes of any viruses that invade the cell.

In a paper published today in Nature Plants, the team shows that a single application of such a spray can stop tobacco plants from succumbing to the pepper mild mottle virus for as long as 20 days. The team explains that the technique works because clay adheres well to the leaves, ensuring that the RNA remains in contact with the plant for as long as possible.

This is by no means the first attempt to use such a tactic to help plants thrive. Monsanto, for instance, has developed its own RNA sprays in the past, but its successes have targeted the insects that consume crops. In those cases RNA kills the pests, rather than equipping the plant with an ability to tolerate the problem.

As our own Antonio Regalado explained when describing Monsanto’s work, using RNA sprays to silence genes has some obvious benefits. They may be faster to create than a whole new strain of genetically modified crop, and could also be used across multiple varieties of plant. And their temporary nature may not necessarily be a hindrance: it could, for instance, allow farmers to turn off gene function only when required.

As New Scientist points out, the potential for such a spray isn’t limited to just preventing disease, either. It could be used to help crops tolerate drought, trigger ripening, or activate some other genetically controlled trait.

Questions will hover over the use of such sprays. Advocates will argue that such RNA isn’t problematic if it enters the human food chain, as it has been shown to quickly break down in the presence of saliva and stomach acids. Skeptics, meanwhile, will argue that a lack of evidence means that the RNA could yet pose a threat to animals, insects, and other plant life.

Like GMOs before it, the promising new technique may struggle to win widespread support—however useful it may be.

(Read more: Nature Plants, New Scientist, “The Next Great GMO Debate,” “Monsanto Cultivates a Rose That Doesn’t Wilt”)