Exotic Weeds in Australia

Case Study - Boneseed and Bitou Bush

The following article was published in the December 1990 issue of "Eucryphia", the Newsletter of the Tasmanian Region of SGAP.

Flower of the Month - Boneseed!

Glenys Jones

Far from advocating the cultivation of this flower of the month, I would like to draw your attention to it, help you to identify it and encourage you to destroy this insidious and invasive weed of natural bushland.


Identification

Boneseed is a soft-wooded shrub up to about 3 m with oval fleshy leaves often with toothed margins. It is easily recognised by its bright yellow daisy flowers. It belongs to the daisy family (Asteraceae) and its scientific name is Chrysanthemoides monilifera. The genus name means "resembling a Chrysanthemum"; the species name means "in the form of a necklace", which may refer to the seeds. Boneseed fruit are green at first, later turning brown to black. Boneseed has no spines or poisons.

   Chrysanthemoides monilifera
  

The attractive daisy flowers of Boneseed may distract attention from the invasive properties of the plant in suitable areas. Photo: Brian Walters


Distribution

Two sub-species have naturalised in Australia, Chrysanthemoides monilifera ssp rotundata (Bitou bush) and ssp monilifera (Boneseed). Bitou bush occurs along coastal areas of southern Queensland, New South Wales and Lord Howe Island. Boneseed occurs in Sydney, southern NSW coast, Victoria, Tasmania and South Australia and in limited occurrences in Western Australia. In Tasmania, infestations occur along the north-west coast and along the Tamar and Derwent Rivers including the suburbs of Taroona and Sandy Bay, Rokeby, and Margate.

The species invades both disturbed and natural areas including coastal heaths, open eucalypt forest, and littoral rainforest communities. It is, however, advantaged by disturbance so that areas of soil erosion and fire-cleared areas are particularly prone to colonisation.


History

Like many of the weeds and pests in Australia, boneseed bush has an interesting history. It was recorded as a garden plant in both Melbourne and Sydney in the mid 1800's. Around 1950, the ability of boneseed to colonize and stabilize disturbed areas was recognised and the species was actively put to use by soil conservation agencies to stabilize coastal sand dunes after mining for mineral sands. However, the success of the species as an invader was underestimated and it has now become established along hundreds of kilometres of coastline along eastern Australia, becoming the dominant species over much of its distribution.

It is one of the few significant weed species of non-agricultural land. It is therefore not a significant economic problem and so tends not to be recognised by State governments as a noxious weed. Boneseed was proclaimed a noxious weed in Victoria because of the direct threat it posed to the structure and composition of native bushland and the indirect threat to birds and animals by the alteration of their habitat.

   Chrysanthemoides monilifera
  

Boneseed has developed a monoculture and displaced native Banksia woodland on these dunes on the NSW central coast. The pink flowers are yet another exotic weed. Photo: Brian Walters


Method of Spread and Control

Boneseed does not normally spread vegetatively. It is all by seed. It is the sheer fecundity of the species or its ability to reproduce huge numbers of seeds that causes all the problems. One mature plant can produce up to 50,000 seeds in one season. And seeds may lie dormant for up to 15 years. The seeds are relatively large and heavy and so tend to drop around the adult plant. But the fleshy drupe is edible and seeds can be dispersed by animals and birds.

Individual plants are relatively easy to kill - by fire, herbicides (Roundup or Zero can be used as a foliage spray at dilution of 1:100 or as a paint on cut stumps at a dilution rate of 1:15) or by physically chopping or hand-pulling them out. Hand-pulling is probably the best method of eradication wherever possible as it offers the advantages of minimising disturbance to non-target species which is particularly important in bushland communities. Re-growth does not occur from roots left in the ground and seedlings are easily pulled by hand.


Ruler
"Hand-pulling is probably the best method of eradication wherever possible as it offers the advantages of minimising disturbance....."
Ruler

Regardless of the method of removal of the adult plant, the real problem lies in dealing with the large reserves of seed left in the ground. As soon as the adult plants are removed, the seeds in the ground will start to germinate and there will be dense re-growth of seedlings. Similarly, seedlings that were content to remain insignificant in the shade of larger plants will burst forth when an opening in the canopy occurs. So follow-up programs to exhaust the dormant seedbank in the soil are an essential part of any serious attempt to rid an area of boneseed.

So, if you know of any infestations of boneseed in your area, I hope you will be encouraged to begin a long and meaningful relationship with this invader and help restore our natural bushland.


Note: Biological control of boneseed and bitou bush is under investigation. Further information is available from the CSIRO's Web Site.


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