Deterring possum browsing with a repellent spray

The outcome

Yates Possum Repellent Spray deters possums from eating plants. The spray can last for up to seven days. Based on natural substances, it can be used on both ornamental and edible plants with only a one-day withholding period.

The spray was developed by Yates Australia using research from the University of Melbourne, and is now widely available for purchase in garden stores around Australia.

The need

Common brushtail possums (Trichosurus vulpecula) and common ringtail possums (Pseudocheirus peregrinus) damage urban parks and gardens in Australia. Both species are native to Australia and are protected by state and federal laws. In the state of Victoria, possums are protected by the Wildlife Act 1975. It is illegal to capture or kill possums without a permit.

Several proprietary possum deterrents are commercially available. Other products – such as fish sauce, animal-based fertilisers or garlic – are also used. However, a study of 14 products commonly used to deter possum browsing found that none were completely effective.

Effective, humane and non-lethal methods are needed to reduce possum browsing.

The research

Biologist Professor Lynne Selwood began investigating methods for deterring possum browsing in the 1980s. Possum deterrents rely on smell, taste or texture to discourage the animals from eating plants.

As a gardener, Professor Selwood wanted to discourage possums from browsing in her backyard. Over several decades, she tested various products, focussing on natural substances. She found that applying pyrethrin, a plant-derived insecticide, to plants could deter possums from browsing. However, pyrethrin degrades in sunlight and is also washed away by rain.

Professor Selwood combined the pyrethrin with diatomaceous earth and mineral oil. Diatomaceous earth is a powder made from the fossils of diatoms – microalgae with a cell wall made from silica. It is used in the garden as an insecticide and in potting soil. This combination of materials helped the pyrethrin solution stick to leaves. It may have also protected the pyrethrin from sunlight.

The solution has been tested by Professor Selwood in her own garden for over 20 years. She also tested it in 10–12 other gardens over three years.

Professor Selwood continues to work at home to improve the spray. She is also working on developing a spray to deter rat browsing in home gardens.

Technology development history

Professor Selwood patented the possum deterrent solution in Australia and in New Zealand. She donated these patents to the University of Melbourne in 2013.

A division of DuluxGroup (Australia) Pty Ltd, Yates Australia licensed the intellectual property from the University in 2014.

Yates worked with Professor Selwood to improve the deterrent solution. The company tested its efficacy in a commercial nursery. The solution was effective in reducing possum browsing for up to seven days after application.

Yates registered the product with the Australian Pesticides and Veterinary Medicines Authority in 2018. Yates Possum Repellent Spray was introduced to the Australian market in 2019.