Biocontrol update at Labelle Station field day

This post is based on a talk delivered by NT Government's Weed Management Branch at a mimosa control field day at Labelle Station on 22 August 2012.

 

A mimosa infestation on the Adelaide River floodplain (grey area)

The wetland weed Mimosa pigra has been the subject of a concerted biocontrol program since 1979. Fifteen agents have been released (13 insects and 2 pathogens), 11 out of 15 have persisted and of those 9-10 are doing good work. To compare, the prickly pear had about 50 agents before it was controlled.

This suite of insects attack different parts and phases of the plant, including roots, thin stems, thick stems, flowers, green seed and brown seed. Together they reduce vigour of the plant, and seed production per square metre has dropped from about 2,000-12,000 to 200.

Biocontrol is an important part of the integrated control of mimosa. Local land manager Colin Deveraux said that biocontrol agents have had a strong impact on mimosa at Twin Hills Station. Seed production has been diminished and plants seem to take three times longer to reach maximum height.

Most mimosa biocontrol agents are mobile and the three most common insects (a flower weevil, a stem tip borer and a leaf feeding caterpillar) are usually always present, even on isolated plants. Agent establishment takes a year or more but once well established, populations cope with fire or herbicide. However, releases should avoid previously sprayed areas that will experience follow up spraying.

Biocontrol agents have been introduced for other weeds, including sida and parkinsonia. Sida is controlled by a leaf-eating beetle called calligrapha. Calligrapha populations fall during the dry season, but can be maintained locally by irrigating a patch of sida.

Biocontrols for parkinsonia have also been successfully introduced, and in July 2012, the Department of Agriculture, Fisheries and Forestry recommended that the release of a new agent, the geometrid moth, be allowed.  

And researchers are currently looking into the use of a fungus for gamba grass.

The NT Government’s Weed Management Branch monitor the presence of mimosa biocontrol agents in different areas and re-release the better performers where they at not present. They also collect calligrapha beetles around January each year and release them where needed. To request a release or visit to check your property for agents, call 8999 5511, or check plants yourself using the links above.