Local release of boneseed predator

MEDIA STATEMENT
August 31, 2007

Local release of boneseed predator

A new organism to help control the pest plant boneseed has been released on Banks Peninsula.

The boneseed leafroller caterpillar (Tortrix s.l. sp.“chrysanthemoides”) was released this week at Diamond Harbour by staff from Landcare Research.

The release and the supporting research is part-funded by Environment Canterbury as part of the national Biological Control Collective.

The caterpillar was first released into New Zealand on Waiheke Island in March this year.

The caterpillars feed on the shrub’s foliage, and they web leaves together to make homes for themselves, which is where the name “leafroller” comes from.

Boneseed is a pest because it has the potential to cause substantial environmental damage in the Canterbury region by invading mostly coastal plant communities. In Canterbury the plant is located on Banks Peninsula and coastal communities between the peninsula and Kaikoura.
“Biological control using boneseed leafroller is the only option for managing this weed in a number of areas,” Environment Canterbury pest and biosecurity chairman Cr Robert Johnston said.

“Using herbicide is often impractical because of inaccessible terrain, and the chance of damaging native plants,” he said.

“A reduction in herbicide use could reduce the damage to non-targeted plants and reduce contamination of soil, air and water,” Cr Johnston said.

Landcare Research, the Department of Conservation and most regional councils nationwide collaborate on projects to control pest plants, by using natural predators of the plants.

People looking for more information on biological control of pest plants can visit: www.landcareresearch.co.nz/research/biosecurity/weeds/biocontrol

Notes for Editors
The plant

Boneseed is a bushy shrub that grows up to three metres high. It has thick, leathery leaves with slightly toothed edges. Masses of bright yellow daisy-like flowers bloom in spring, followed by clusters of fruit that turn black when ripe. The single seed inside is very hard and the colour of bone, hence the name. A very hardy shrub that can grow in a variety of soils, it is frost-resistant, and tolerant of semi-shade, drought and salty environments.

The problem

Boneseed colonises low coastal and open vegetation. It shades out native tree seedlings and can invade coastal cliffs, sand dunes, scrubland, roadsides and offshore islands. Its thick growth can restrict the use of beach areas, especially sand dunes. It can be spread widely when birds and possums eat the fruit and distribute the seed in their droppings.

Boneseed in Canterbury

In Canterbury the major areas of infestation are in the Port Hills of Banks Peninsula. It has occupied coastal cliffs and ungrazed land set aside for development, and coastal sand dune areas to the north of the estuary where it has filled a niche created by the decline of the tree lupin (Lupinus arboreus).

Controlling it

Boneseed is a biodiversity pest plant in the Canterbury region and is also on the National Pest Plant Accord list. This means the plant is banned from sale, propagation, distribution and commercial display within New Zealand.

Smaller plants can be hand-pulled and larger plants cut off close at ground level and the stump treated with herbicide. Boneseed can also be controlled by a suitable herbicide but this is difficult in inaccessible terrain.

A new tool - boneseed leafroller

The adult leafrollers are mottled earthy-brown in colour with a darker narrow zig-zag band across the wing, 9.5mm long, and at rest their wings form a triangular shape. They live for about 14 days.

The leafrollers lay pale yellow eggs on the boneseed leaves which hatch into olive-green coloured caterpillars. These move to the shoot tips to feed and web neighbouring leaves together to form a shelter. Older caterpillars are dark green to black in colour with two parallel rows of white spots along the length of the body.

ERMA determined that risk to non-target plants is negligible, and the potential positive effects of the release far outweighed any potential adverse effects.
Its decision outlines the science supporting that conclusion.

Successful establishment of the leafroller should result in less herbicide use and therefore less damage to non-targeted plants.

ENDS

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