Weeds - Phase 1 - Research Highlights

Biological control of giant Parramatta Grass

What the report is about

Giant Parramatta grass (GPG) (Sporobolus fertilis) is an aggressive perennial tussocky grass that is a declared noxious weed. It invades native pastures and reduces animal production. Its potential distribution is estimated at 23.7 million hectares in Australia.

The naturally occurring fungus, Nigrospora oryzae, causes a crown rot in GPG which has now been shown to reduce tussock size dramatically in the field.

Where are the relevant industries located in Australia?

GPG invades native pastures and reduces animal production. Its potential distribution is estimated at 23.7 million hectares in Australia

Aims/objectives

To evaluate the potential of Nigrospora oryzae for biological control of weedy Sporobolus species in Australia by:

• A postal survey and local surveying of impacts in the field
• Estimates of carriage and impacts in posted plants in a glasshouse
• Collection and testing of other provenances of plants and strains of fungi
• Identification of any resistance in plants and the greatest virulence in fungal strains
• Host specificity testing
• Development of an inoculation method for fungus
• Field inoculation and monitoring of impacts.

Results/key findings

• The control process can take a couple of years, which allows the remaining pasture species to recover and fill in the gaps left by the dying GPG.
• Laboratory tests have shown a 70 per cent reduction in healthy GPG leaves seven months after plants were inoculated with a solution of fungal spores.
• Disease symptoms are most apparent seven to 10 days after rain in spring and summer.
• Diseased plants produce orange leaves in their new growth, which then die.
• Individual diseased tillers can be broken off at their base where the normally white crown tissue has turned black and died.
• Recent observations have shown that this disease does not affect giant rats tail grass, which is the same genus as GPG, but is known to be genetically different, which suggests the disease is quite host-specific.

Postal survey responses revealed that land managers had noticed the disease was causing a decline in giant Parramatta grass and had therefore reduced or ceased applying herbicide. This had saved almost $10,000 at Nana Glen in the preceding year­ - chemicals, labour, fuel and associated withholding period costs - and had reduced associated environmental costs.

Respondents also noted the need for cooperative efforts, including on roadsides, and expressed a desire to control GPG and other weeds, particularly Bahia grass. The respondents were keen to know the outcomes of the research and to participate in a local biocontrol to control GPG without constantly using mechanical or chemical means.

Implications for relevant stakeholders

Once all safety requirements are met this herbicide has the potential to be commercially viable for effective control of GPG, which affects large parts of the North and Mid North Coast. Cultivation of the disease in the laboratory is relatively simple, suggesting commercial propagation of the disease for a mycoherbicide will also be attainable.