Navua sedge specimen captured during field research in Madagascar. Credit: CABI

Previous Next

Project Overview

So, what’s the problem

Cyperus aromaticus (Cyperaceae), commonly known as Navua sedge, is a perennial, rhizomatous (a plant with a stem growing horizontally, just below the surface that can produce interspersed roots and shoots creating a root system) sedge native to equatorial Africa and countries in the western Indian Ocean.

It is now recognized as a noxious invasive weed in Southeast Asia and several South Pacific Islands. In Australia, the weed has become an aggressive invader since its introduction to the wet tropical regions of northern Queensland in the 1970s.

Navua sedge has significant negative impacts on native grassland biodiversity and on the beef, dairy and crop farming industries. The sedge is unpalatable and can form dense stands by replacing palatable tropical pasture species. Current management options for controlling this weed rely on chemical and mechanical methods, which are costly, often unsustainable and provide only short-term relief. As a more cost-effective and long-term management solution, Navua sedge has been approved as a target for biological control in Australia.

In 2017, DAF, Australia, initiated a biological control programme against Navua sedge, starting with field surveys in the native range of Kenya, Nigeria and Tanzania to identify natural enemies of this invasive weed.

What is this project doing?

CABI scientists are assessing two fungal pathogens collected from Nigeria and Tanzania for their potential to control Navua sedge. The pathogens currently being investigated are the smut fungus, Cintractia kyllingae, which infects the florets of the inflorescence on Navua sedge, and the rust fungus Puccinia kyllingae-erectae (Uredo kyllingae-erectae), which attacks the leaves and stems of the weed. To effectively control this invasive weed, multiple agents that target different parts of the sedge may be necessary to reduce seed production and limit the weed’s spread.

To evaluate their suitability as biocontrol agents, experiments will be conducted in under quarantine conditions to determine their respective life cycles and infection parameters, including the optimal temperature and dew period for infection.

Host-range testing will be undertaken against selected test plant species to ensure that these pathogens are highly host-specific and do not pose a risk to native Australian plant species. The results will help determine whether these fungal pathogens are safe and effective candidates for introduction into Australia.