New Zealand EPA approves release of moth plant rust fungus

The New Zealand Environmental Protection Authority (EPA) has approved an application to release the moth plant rust fungus Puccinia araujiae to help control the moth plant weed (Araujia hortorum).

The application, from Northland Regional Council, on behalf of the National Biocontrol Collective (12 regional/unitary authorities and the Department of Conservation) was made under the Hazardous Substances and New Organisms (HSNO) Act 1996.

The rust fungus Puccinia araujiae is a highly specific parasitic fungus that is expected to severely impact on moth plant, its primary host. The typical symptom of the fungus is rust-coloured lesions on the plant leaves and fruit, causing defoliation and killing the plant’s stems. The fungus will also limit seed production, which will in turn inhibit the spread of the moth plant to new sites.

“Manual control of the moth plant weed is time consuming and has only had limited success,” said Sarah Gardner, General Manager Application and Assessment.

“The application approved suggests the introduction of the rust fungus as a biological control agent will likely reduce the spread of the moth plant. Reductions in the abundance of moth plant populations may also deliver biodiversity and conservation outcomes.”

Moth plant belongs to the sub-tribe Oxypetalinae. Other members of this sub-tribe, including the exotic ornamental tweedia (Oxypetalum caeruleum), will possibly be affected by the fungus. If necessary, home gardeners could mitigate damage to tweedia by applying an over-the-counter fungicide. There are no native species that belong to the same sub-tribe or tribe as moth plant therefore no native New Zealand plants are expected to be harmed by the fungus.

Moth plant is a tough perennial, broad-leaved herbaceous climber with twining stems, clusters of small cream tubular flowers and choko-like fruit. It can reach over 5 metres when it grows up trees or creeps over the ground, shading out low-growing vegetation. The sap of the fruit and stem is a skin irritant. The weed is considered a threat and cannot be sold, propagated or distributed in New Zealand. Some regional councils require landowners or occupiers to remove moth plant from their property.

The plant is native to south-east Brazil, Argentina, Paraguay and Uruguay. It has become naturalised in a number of countries and has been regarded as a weed in most countries it has colonised. In New Zealand, moth plant is widespread in Northland and Auckland and found throughout the Coromandel, Waikato and Bay of Plenty. There are also sporadic infestations in the Wellington region and around the top of the South Island.

The rust fungus is the second biological control agent approved for release under the HSNO Act to control moth plant. The first agent, the beetle Colaspis argentinensis, was approved in 2011 but has not yet been released. If the beetle is released, the two agents are expected to work together to suppress the moth plant.