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Stand By to Repel Browsers

Poison baits and shooting may not be the best ways to prevent pests such as rabbits and possums from destroying vegetation, say Landcare Research scientists. Improved repellents could provide a cheaper and safer means of control.

"Repellents have the advantage of being easy and safe to apply because they don't use toxic substances," says researcher David Morgan. "Also, they are cheap compared to animal control or tree shelters."

In the late 1980s, Forest Research Institute scientists developed a repellent based on egg powder and acrylic paint. Now marketed as Treepel, this provides six months of protection for a few cents per plant.

The Landcare researchers are working to improve the durability of repellents. Experiments are also under way to see if the intensely bitter substance Bitrex can be taken up by a plant into its leaves.

Other trials are investigating whether repellents can be fixed to leaves like some herbicides, or incorporated into plastic mouldings surrounding seedlings for slow release over several years.

Another possible deterrent is the scent glands and waste products of predators such as foxes and stoats. Overseas results indicate that browsing declines in the presence of predator odours, so this may be a possible form of biological control if New Zealand rabbits and possums respond similarly.