Biological Control

Biological control is a long-term management option that uses the natural enemies of a weed, such  as insects (moths, beetles) or fungi (rusts, smuts), imported from the weeds country of origin, to slowly reduce its density in Australia over time.

Biological control is not a silver bullet. A biological control program may take years or decades to become established and will never eradicate the weed. Instead, it may reduce the weeds competitiveness and limit its impact.

The process of finding a biological control agent is long, with no guarantees of success. Before a potential agent can be released, it must be stringently tested to ensure it does not attack native species that are related to, or similar to, the target species. For serrated tussock, species such as spear grasses (Austrostipa spp.) and beneficial introduced grasses (phalaris and perennial rye grass) are among many species that have to be tested.

No biological control agents are currently available for serrated tussock in Australia.

The rust fungus Puccinia nassellae has been identified attacking serrated tussock in Argentina. - Source: Dr Freda Anderson, CERZOS, Argentina

Smut fungus Ustilago spp. has the ability to stop serrated tussock from reproducing. - Source: Dr Freda Anderson, CERZOS, Argentina

Potential for serrated tussock biological control in Australia

Serrated tussock was declared a target for biological control in 1999. Previous work had determined that insects were not sufficiently host specific for biological control of serrated tussock. A group of organisations (NSW Shires, Meat and Livestock Association, State Governments, Federal Government) have funded the exploration and testing of potential pathogens for biological control agents of serrated tussock found in Argentina and South America. Three potential agents have been identified and tested to date. Unfortunately, none of these pathogens look like a suitable candidate for biological control of serrated tussock in Australia.

1. A rust fungus, Puccinia nassellae, was identified attacking serrated tussock in Argentina and in some instances, was observed killing plants. However, due to issues of its host specificity, mass rearing and uncertainties of its life cycle, it is unlikely that this rust fungus will be progressed as a biological control agent.

2. A smut is a fungus that destroys the plants seeds—mostly infecting the plant at seed germination or during the seedling stage. It does not kill the plant, but prevents it from reproducing. A smut infecting serrated tussock, Ustilago spp., was found in isolated populations in Argentina. Attempts at culturing this smut have been largely unsuccessful to date, and only three plants of more than 500 inoculated with the smut, became infected. Further research is required to progress this potential biological control agent.

3. A Corticium spp. fungus has been identified killing serrated tussock plants in Argentina. It is a soil borne fungus that rots the crowns and roots of serrated tussock. It has not been possible to culture this pathogen making it an unlikely biological control candidate.

An observation made in Argentina by scientists is that they rarely see serrated tussock seedlings, suggesting that a potential area of investigation is the serrated tussock seed bank and its associated soil pathogens.

If land managers observe serrated tussock plants dying or sick for no apparent reason, it is important they report this to their local weeds officer. Call DEPI on 136 186 in Victoria.