Deterring Possums with Pyrethrum

by Priya Mohandoss

After noticing the presence of both brush-tailed and ring-tailed possums foraging around and damaging the plants in her backyard, zoologist and keen gardener Professor Lynne Selwood came up with the idea to develop a substance that could preserve and protect her beloved plants from browsers, i.e., animal species that use trees for their habitat and something that was readily accessible for all to use.

During the first five years, she conducted a series of independent experiments, choosing particular plants from her garden that were inedible to possums, such as jasmine. Then, similar to an herbalist, she made a concoction; diluting the chopped leaves with water in order to form a spray.

However, all the plants that Lynne tested proved to be irritants and had much toxicity. It was only when she used pyrethrum, an organic compound found in Chrysanthemum cinerariifolium and Chrysanthemum coccineum, to deter pests from her citrus trees that she discovered that possums withdraw from it as well.

Lynne Selwood
Professor Lynne Selwood FRSV with her Possum Repellent spray, produced by Yates. Photo: Priya Mohandoss

Although she had found the active component in pyrethrum acted as a deterrent, the drawbacks were that it deteriorated in sunlight and easily washed off leaves in rain. As a result, it took a further fifteen years to solve how pyrethrum could be fixed in its effective, oily phase. Yet after examining the principles of radial symmetry and diatoms (micro-algae found in oceans), Lynne discovered that diatomaceous earth, a natural occurring mineral made from diatoms and containing silica, resolved the matter.

Her next step was to approach the Commercialisation Unit at the University of Melbourne. After doing more assessments with the product, the spray was then patented and then presented to gardening product manufacturer Yates. As they say, the rest is history!

The spray is now available for commercial use with the patent and a portion of the proceeds going to the University.

Being a problem solver and having a continued interest in browsing animals, Lynne is now in the early testing phases of determining a substance that has the capability to deter rats from targeting a variety of plant species, particularly tomatoes and citrus trees.

Congratulations Lynne!

Yates Possum Repellent 1 litre spray is available from Bunnings Warehouse.