AN army of very hungry caterpillars, incubating in the Barossa Valley, will soon be ready to gorge on a noxious weed across the Northern and Yorke regions.

The horehound plume moths, currently in a nursery at Rosedale, are expected to be ready to attack this month.

Known as host specific, plume moths only have a taste for the invasive horehound weed, with the larvae feeding on the growing tips, weakening the plant and reducing the flowers and burrs.

Northern and Yorke Landscape Board landscape officer David Hughes said during an initial trial in the region, in 2018, a batch of moths eliminated 75 per cent of a five-hectare infestation in less than a year.

“Not only did our 60 original very hungry caterpillars increase and decimate the horehound on the host property, but we found the caterpillars had spread to three adjoining properties and roadsides where they were busy attacking the weeds, turning them into sticks,” he said

“Some farmers have suggested these moths act like a thousand sheep that have come in and eaten the weed back to its roots.”

On the sheep property of Gawler’s Brian Sambell, near Burra, a 50 square-metre patch of horehound has completely disappeared after plume moths were released there about two years ago.

“It certainly works,” Mr Sambell said.

“I couldn’t show you a horehound plant where I released the caterpillars now. They’re all gone.”

Horehound has a distinct odour that taints milk and meat when consumed by stock. Seeds are dispersed when its tenacious burrs get caught in wool, fur or clothing, with large mature plants producing in excess of 20,000 seeds per year.

Landscape officers from the Northern and Yorke Landscape Board will be ready to supply free plume moth larvae to landowners with horehound infestations in September.

To express interest, landowners should contact the Northern and Yorke Landscape Board (8841 3400).