Very hungry caterpillar tackles horehound weed

News release
09 November 2017

Adult horehound plume moth

Adult horehound plume moth

An effective biological control against a noxious weed has just been re-released north of Gawler.

The horehound plume moth (Pterophorus spilodactylus), first released 20 years ago to tackle horehound weed (Marrubium vulgae), is flourishing on recent infestations boosted by ideal growing conditions.

Natural Resources Adelaide and Mt Lofty Ranges (AMLR) District Officer David Hughes says the generous rainfall this year had created a perfect environment for the pest plant to thrive.

“We’ve been aiming to reduce the weed using one of the best weapons, a natural biocontrol called horehound plume moth,” Mr Hughes said.

Caterpillar of horehound plume moth

Caterpillar of horehound plume moth

“Some farmers have said the moth is so effective that when it goes to work, ‘it’s like a thousand sheep have come in and eaten the weed back to the roots’.”

Horehound plume moth caterpillar damage

Horehound plume moth damage

Landowners recently asked Natural Resources AMLR for help with an infestation of horehound at a Rosedale property.

Officers from the Gawler Natural Resource Centre collected horehound plume moth caterpillars from bushes around the district.

Then they applied these grubs to a large five-hectare infestation of the weed to the property in Rosedale, spreading about 60 of the caterpillars among the plants. Officers expect the grubs are already on the job and devouring the horehound.

David Hughes and Jamie Pook spread horehound plume moth caterpillars

David Hughes and Jamie Pook apply horehound plume moth caterpillars on horehound weed

Horehound, traditionally used to make beer, is an introduced perennial herb that can grow out of control if not managed. It invades rural properties and contaminates the meat, milk and wool of livestock that eat it.

The horehound plume moth was first introduced by Natural Resources AMLR to the area in 1997.

The grub is host specific and will only feed on horehound. When active, it can heavily reduce the seeding capability of this pest plant and reduce the size of infestations.

“Horehound plume moth is one of a number of biocontrol agents and also part of an integrated approach to help control weeds,” Mr Hughes said.

Landowners have a legal responsibility to control the spread of horehound weed under the South Australian Natural Resources Management Act 2004.

For assistance in managing this or other weeds, please contact the Natural Resources AMLR Gawler office on 8523 7700.

Photos courtesy of Dragos Moise.

More information

Natural Resources Adelaide and Mount Lofty Ranges