A University of Queensland PhD student is assisting efforts to control a tropical American shrub that is choking native vegetation in northern Australian wetlands.
Plant pathologist Bertie Hennecke is assessing the use of a fungal biological control to curb the spread of Mimosa pigra, also known as the giant sensitive plant, which is declared a noxious weed in Australia.
The weed, a woody perennial shrub, was introduced to the Darwin Botanical Gardens around 1870. It spread rampantly in the 1970's and now covers approximately 800 square kilometres of wetland and conservation areas in the Northern Territory.
On reaching its favoured habitat on the coastal floodplains, it has become invasive, completely changing ecosystems and displacing native vegetation. It is also menace to pastoralists as it renders land useless for grazing and makes mustering virtually impossible. In addition to these changes the giant sensitive plant prevents access to recreational fishing sites and impacts on cultural significant areas for Aborigines.
"In Central and South America the plant rarely reaches two metres, but in Australia it grows to six metres forming dense, impenetrable, thorny thickets," Mr Hennecke said.
"The seeds can float, and spread rapidly from the source of production. The difficulty is the plant has no natural enemies to keep it under control in Australia, while it does in its natural environment."
The Northern Territory and Commonwealth Government are funding an integrated management program in the battle against the feral, triffid-like invader.
Mr Hennecke, a biological control officer for the Northern Territory Department of Primary Industry and Fisheries, based in Darwin, is conducting a PhD study supervised by Drs Michele Dale of UQ's Botany Department, Karen Gibb of NTU (both of the CRC for Tropical Plant Protection), and Anna Padovan (CSIRO).
He said chemical, physical and mechanical methods are important for managing infestations of the plant but the continual use of large amount of chemical herbicides over vast areas is both uneconomic and environmentally undesirable.
"Biological control - introducing natural enemies - is likely to be one method for long-term control of this vigorous weed," he said.
Since 1979 detailed surveys conducted by CSIRO Entomology in Central and South America for potential biological control agents, have resulted in the release of nine insects and two pathogens in the Northern Territory.
One of these is a Mexican fungus, Phloeospora mimosae-pigrae, introduced and released in Australia in 1995. It has passed scrupulous international testing to ensure it is specific only to the giant sensitive plant.
Mr Hennecke has conducted experiments to develop inoculation and cultivation techniques using the biological control agent.
In pilot studies he waded through knee-deep water in crocodile and mosquito-infested areas carrying a backpack full of the fungus to spray infestations of the giant sensitive plant. Helicopter spraying of the fungus using Global Positioning System technology has proved a safer personal option.
But the Mexican isolate has not proved as effective in Australia as in glasshouse trials in the United Kingdom, or in the field in Central and South America.
The fungus is relatively new to science and not much literature has been developed and its evolutionary tree is relatively unknown.
In 1998 five new strains from different locations in Central and South America were imported in Australia. Mr Hennecke is comparing them in genetic and shade house studies with the Mexican isolate for effectiveness.
He said the poor long-term performance of the Mexican strain and the importation of five new strains from different locations provided an opportunity to determine the most suitable strain for environmental conditions in the Northern Territory.
European-born Mr Hennecke is finding out more about the fungus and its related family.
Mr Hennecke said his Northern Territory career was a far cry from his undergraduate tropical agricultural studies at the University of Kassel in Germany, but more "exciting and adventurous."
"Australia offers many research opportunities for people of science," he said.
"It is an exciting work environment, because so many things here remain undiscovered."
Media: Further information, Bertie Hennecke (08 8999 2327)
