​​​​Australian myrtle (Leptospermum laevigatum) (Myrtaceae)

The Weed

Leptospermum laevigatum is commonly known as the Australian myrtle, tea tree or coastal tea tree. This species is native to Australia, occurring from Queensland, through to New South Wales, Victoria, South Australia and Tasmania. It is a shrub or tree capable of reaching a height of 8 metres. In areas where L. laevigatum occurs, few native species are able to survive, due to the competitive nature of the weed, exacerbated by their growth form, shading out any underlying areas so that they become unsuitable for other species. The species is able to tolerate a wide range of climatic conditions, growing in both winter rainfall areas, as well as regions experiencing year-round rainfall. It is a major problem in mountain and lowland Fynbos areas, and also occurs in southern forests. 

The plant was originally introduced to South Africa as a hedging plant and a windbreak, but has also been used for ornamental purposes. It is a highly invasive species, being classified as a Category 1b invasive species, according to NEMBA classifications. It occurs mostly in the Western and Eastern Cape Provinces of South Africa, with current hotspots for distribution occurring around the Hermanus and Stanford areas in the southern Cape. The plant is able to propagate quickly post-fire, which contributes to its invasive ability. Australian myrtle flowers during spring in its second or third year, producing small white flowers. The fruits, containing the seeds, are not released from the tree until after the tree dies, usually as a result of felling or fire.  

​​Leptospermum flowers​​​​​​Leptospermum infestationLeptospermum branchLeptospermum flower & fruit

Control options

Mechanical control is, currently, probably the most effective form of control against Australian myrtle. If plants are removed within their first three years, the invasive potential of populations can be drastically reduced, because seeds are only produced in the plant’s second or third year. Furthermore, seeds are not very long-lived within the soil because they do not have enough nutrient supplies. Controlled burning of infested areas is also an option for control of the spread of this weed. 

Two species of insects have been introduced into South Africa in an attempt to use biological control to hamper the spread of the Australian myrtle. The first of these, a bud-galling midge, Dasineura strobili, was inadvertently introduced in the 1980’s and, initially, had promising prospects as a biocontrol agent. However, there is presumed to be much parasitism and predation of the midge, reducing its efficacy as a control agent. The second potential biocontrol species is a leaf-mining moth, Aristaea thalassias, introduced in 1996. This species only attacks young leaves and causes leaf-abscission, having relatively negligible impacts on the survival and growth of mature L. laevigatum trees. It is hoped that investigations into a third potential biocontrol agent, in the form of a gall-inducing scale insect, Callococcus leptospermi, will yield good results in terms of negative impacts on Australian myrtle in its native range, with the hopes that this species may be imported into South Africa for release, within the next few years. 

​​Further information

The following documents can be downloaded:

  • A review of the biocontrol options for this species, which was published in 2011: pdf​
  • A fact sheet on this weed: pdf​ .

​Contact: Dr Candice-Lee Lyons at LyonsC@arc.agric.za​.