Weeds in our Area (Part Forty One)
By Bob and Ena McIntyre – Garden Route Branch.
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..
Indigenous Alternatives: Trapa natans – Water chestnut, Utricularia inflexa – Bladderwort
Line drawing with acknowledgements to “ALIEN WEEDS AND INVASIVE PLANTS” by Lesley
Henderson. Copyright © 2001 Agricultural Research Council