Farmers’ hearts a-flutter over weed-killing moth

David Hughes and Jamie Pook release horehound plume moth
David Hughes and Jamie Pook release horehound plume moth

Some very hungry caterpillars have been using their extraordinary eating skills to reduce a noxious pest north of Gawler.

Last October a biological control agent called the horehound plume moth (Wheeleria spilodactylus) was released on a Rosedale site infested by the difficult to eradicate horehound weed (Marrubium vulgare).

Horehound has a distinct odour that taints milk and meat when consumed by stock. Its tenacious burrs get caught in wool, fur or clothing and large mature plants can produce in excess of 20,000 seeds per year.

The results were remarkable with 75 per cent of horehound eliminated from the five hectare infestation in Rosedale in less than a year.

Natural Resources Adelaide and Mt Lofty Ranges (AMLR) District Officer David Hughes was ecstatic about the results of the trial.

“The drier conditions seem to have provided perfect conditions to increase the population of the plume moth and allow them to flourish,” Mr Hughes said.

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

“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 are busy attacking the weeds there, turning them into sticks, much to the delight of the landowners,” Mr Hughes said.

Plume moths are host specific, feeding only on horehound and do not attack any commercial crops or native plants.

Plume moth larvae feed on the growing tips of the horehound, weakening the plant and reducing the number of flowers and burrs produced.

More work to control this weed has commenced with the AMLR team identifying horehound sites along the rail line from Kapunda to Eudunda as well as sites in Tarlee, Penrice, Two Wells and Dublin for the next release of plume moth larvae.

The team will also be supplying caterpillars to several landholders on adjoining Natural Resources areas further north in the Burra and Halleluiah Hills region.

For assistance in managing horehound or other declared weeds, please contact the Natural Resources AMLR Gawler office on 8115 4600.

A decimated horehound leaf

A decimated horehound leaf