Background

What is the weed problem?

Cabomba is a sought after aquarium plant for its delicate appearance, and consequently was introduced into Australia for aquarium trade. Improper disposal of the plant into natural water bodies by aquarium owners or commercial producers has resulted in infestation of permanent slow moving water bodies, lakes and streams in eastern and northern Australia. It can reproduce vegetatively from small stem fragments, and hence it is easily spread in the absence of appropriate hygiene practices (e.g. washdown of recreational boats when moving between water bodies). Cabomba infestations negatively affect water quality, recreational activities and aquatic biodiversity. It can grow in a wide range of climate conditions from monsoonal tropics to cold temperate environments, and infestations have been recorded from Melbourne to Darwin.

How is the weed currently managed?

Cabomba is currently managed by mechanical removal and herbicides. However, herbicides have been difficult to apply to submerged plants and their use is highly restricted in potable water systems. Mechanical removal is expensive and hence only used in recreational areas to improve public access. Repeated removal is often necessary as plants grow quickly after removal. Mechanical removal can potentially spread the weed beyond the infested water body, as cabomba can easily break into stem fragments when disturbed, and grow new plants from these fragments. Lowering of the water level (draw down) to dry the weed, in combination with herbicides and shading, to restrict light, have been used to manage cabomba in smaller water bodies.

What can biocontrol offer to the weed’s management?

Biocontrol could be a vital tool in potable water systems invaded by cabomba, given the restrictions of using herbicides and the costs of other control methods in these systems. A successful classical biological control program for cabomba would enable a reduction in costs of managing this water in potable water systems, and enable integration with mechanical and chemical control methods in other freshwater systems. By reducing the local abundance of cabomba, biocontrol should also limit the risk of spread of this weed.