Azolla filiculoides Lamarck (Pteridophyta: Azollaceae), its status in South Africa and control

Azolla filiculoides Lamarck (Pteridophyta: Azollaceae) (red water fern) is native to South America and was first recorded in South Africa in 1948. The lack of natural enemies and the presence of enriched waters have contributed to its establishment throughout the country where dense infestations cause severe degradation of aquatic ecosystems and limit their utilisation. The biology of A. filiculoides precludes it from being controlled manually or mechanically and herbicidal control in the aquatic environment is undesirable. Biological control is suggested as the only sustainable control method for this weed and a natural enemy, Stenopelmus rufinasus Gyllenhal (Coleptera: Curculionidae), was released for this purpose in late 1997. The weevil has established well and has caused a significant decline in the Azolla mat at a number of sites, suggesting that the weevil will be an efficient tool in the management of A. filiculoides in South Africa.