Biological control of Navua sedge (Cyperus aromaticus) in Australia

Abstract

Navua sedge (Cyperus aromaticus), a native of equatorial Africa, is an extremely aggressive perennial sedge, affecting beef, dairy, and sugarcane industries in the wet tropical regions of northern Queensland, Australia. Navua sedge is also a major weed of crops and pastures in Fiji and other South Pacific Islands. Navua sedge is unpalatable and forms dense stands that can replace palatable tropical pasture species. Current management options are mechanical and chemical, which are expensive and offer only short-term relief. Biological control is considered the most cost-effective and long-term management option. Navua sedge has been approved as a target for biological control in Australia, where a biological control program was initiated in 2017.Native range surveys in Kenya, Nigeria andTanzania found three promising biological control fungi; specifically, a smut fungus (Cintractia kyllingae) that infects flower heads and seeds; a rust fungus (Uredo kyllingae-erectae) that attacks leaves and stems; and an inflorescence-colonising ascomycete (Curvularia tanzanica). Field surveys have only recorded these fungi in association with Navua sedge. For effective biological control of Navua sedge, multiple agents that target different parts of the sedge maybe needed to reduce seed production and minimise its impact and spread. These three fungal pathogens have been exported to CABI-UK, where host-specificity testing for C.kyllingaeis in progress; and testing for U. kyllingae-erectaewill commence soon. If proven to be host specific, the pathogens will be released in Australia. Current research in Australia has focused on the search for local pathogens on Navua sedge that may have potential as mycoherbicides. Several fungi of interest have been found in Australia, including species of Curvularia, Epicoccum, Fusarium, Neopestalotiopsis, Nigrospora, and Phaeosphaeria, as well as other fungal pathogens yet to be identified.