Azolla sp. (Red Water Fern) Still on a water-weeds theme we look at yet another invasive that has found its way into our region. Azolla (commonly known as red water fern, rooiwatervaring or red azolla) has three species of which A. filiculoides (originating from North, Central and South America), is the most important in our country. Being brought into the country in the 1950’s probably as an aquarium plant, it has now established itself from the Gariep Dam as far as Mpumalanga and has also been found in the Durban area. Locally it was spotted in a small dam on a golf course – very typical of where it usually occurs. It is classified as a Category One weed under the Cara Regulations.
Impacts:Azolla clogs waterways and creates sheltered breeding areas for pests such as mosquitoe larvae and bilharzia carrying snails, as well as rendering the water surface-area unusable for birds, other wildlife and people.
Identification: The plant is a true fern and reproduces by division and also produces spores. Such spores are transported over long distances by floodwater, birds and animals. Very interesting is that azolla has a symbiotic relationship with the blue-green alga Anabaena azollae. This relationship enables azolla to be self- sufficient in its nitrogen nutrient requirements.
Control: The best and most successful method of control is physical removal of the plants. Biocontrol has also proven effective; a leaf chewer was released in 1997. No herbicides have been registered for the control of A. filiculoides..