Tradescantia fungus to tackle pest plant in Hamilton

Leaves infected with the tradescantia yellow leaf spot fungus.

A spotty fungus is the latest arsenal in the toolbox to tackle a widespread pest plant, and it has just been released in a Hamilton park.

The tradescantia yellow leaf spot fungus is native to Brazil and was imported to New Zealand by Landcare Research for the first time last year.

This is only the second time it has been released in the Waikato.

"Three species of tradescantia beetle have previously been released in different parts of the Waikato, with each one attacking different parts of the plant," said Waikato Regional Council biosecurity pest plants officer Hamish Hodgson.

"The beetles have established really well, and at Hahei we've even been able to harvest beetles and release them in other areas," he said.

But the beetles have a big job ahead of them, and at sites which experience flooding the insects struggle to survive.

"That's where it's hoped the fungus will be able to help. Last week we planted 10 tradescantias already infected with the fungus in Edgecumbe Park. We'll be checking on the area regularly to track the spread of the infection," said Hamish. Infection begins when spores germinate on the surface of tradescantia leaves. This requires moisture.

The fungus then penetrates the leaves and they eventually shrivel and die.

"Because this plant is so widespread in New Zealand, manual or chemical control on a large scale is simply not feasible. That's where biological control — or biocontrol — comes in," said Hamish. "It uses a living organism to control another, and it's a method that has been used very successfully across New Zealand since the 1920s to safely control a number of different weeds."

Tradescantia — also known as wandering willie — smothers the ground, preventing native tree regeneration. The plant is also a nuisance for home gardeners and causes allergic responses in dogs.

Stem fragments are spread by water movement, livestock, dumped vegetation, soil movement, boots and mowers.

For more information visit weedbusters.org.nz.