Control for Bridal Creeper on Kangaroo Island

from A.P.S. Journal, February 2002, 17(1) by Beverley Overton

On Kangaroo Island there currently are field trials of two biological control vectors that are specific to bridal creeper: a leaf hopper and rust fungus. These field trials are secondary to the use of appropriate herbicides that continue to be the primary control method. This report focuses on the effects of rust.

A single bare-rooted bridal creeper, infected with rust, was donated to the Kangaroo Island Animal and Plant Control Board in August 2000. This had been placed in a pot of moist potting mix for ease of transport by plane and has been used with much success.

Rust pustules change the bridal creeper leaf colour from green to yellow and, over time, defoliate the plant thus reducing its ability to take up nutrient to ‘feed’ its underground tubers. Depending on the weather conditions it can take from 24 to 36 days before the first sign of yellow flecking is visible, and a further 5 to 7 days for the rust (pustules) to mature sufficiently (become active) to spread by the breezes or direct contact to nearby leaves. Rust fungus has an over-summering stage. This means that it is only active in winter at the same time bridal creeper is growing. So, they both ‘rest’ in summer, as does the leaf hopper.

Initially it was hoped to have between 65 to 100 of pots of bridal creeper inoculated with rust fungus by May 2001 for community members to use amongst their patches of dense bridal creeper. Vandalism caused some set back, with some 50 pots being damaged. Pots were up-ended, and soil, plants and pots were removed and the signs and recycled plastic stakes destroyed. Luckily not all of the pots of young bridal creeper had been put into the field because, at that time, their leaves had not expanded sufficiently for inoculation. By mid-September 2001, the Animal and Plant Control Board was still able to involve 35 of the community members who had registered their interest in participating in this particular bio-control on their properties, as well as continuing inoculation at selected sites.

Each pot of infected bridal creeper was accompanied by verbal and written instructions so that recipients learnt how to maximise the use of their pot of rust fungus. These community persons have been asked to record their success or failures on a form so that the information can be used towards future releases of bridal creeper rust on Kangaroo Island and other affected Australian states.

None of this year’s program could occur until rust reappeared on the ‘wild’ bridal creeper. The heavy June rainfall was sufficient to reactivate rust fungus in the Kangaroo Island Council and privately owned bushland near Little Brownlow, and rust first became evident on leaves on 3 July 2001. Infection by rust has been very slow to show on the leaves and distribution has been patchy, but outcomes have been positive. The bushland sites have been monitored for natural spread of rust fungus by wind and rain – by 27 September 2001 rust had spread 14 metres by 5 metres from site 1. From site 2 its spread is 5.5 metres by 5.5 metres. From sites 3 and 4 spread has been almost 3 metres by 1 metre but at site 5 it has only moved 25 centimetres. Children playing and making cubby houses out of bridal creeper have heavily disturbed this last site. In two sites the rust fungus did not naturally reactivate.

Herbicide will continue to be the primary control until the huge masses of bridal creeper are reduced significantly. In 1996 the Animal and Plant Control Commission (SA) provided funds to begin using herbicide on bridal creeper in and near Kingscote. The success of this small project started the ball rolling and now we are getting some great results, both in reduction of infestations, and funding. Biological control with rust fungus and leaf hopper will in time reduce the bridal creeper. But, these vectors can only be effective if we (community, business, rural and city members) continue to work together towards a common goal.

The Kangaroo Island Bridal Creeper Control Committee will release a report on their entire program in due course. The Native Vegetation Council and the Animal and Plant Control Commission provided funds for the initial project. This work would not have been possible without the support and assistance of the local people, assistance for which I and the KI Animal and Plant Control Board are truly grateful.

The spots visible on the leaves on the left are rust pustules. At this stage they show as yellow spots on the green leaves. The leaves on the right have active rust pustules.