Ebsford Environmental worked in partnership with London Borough of Lewisham and The Friends of Beckenham Place Park to manage an Azolla issue at Stumps Hill Pond, part of Beckenham Place Park.
Azolla is a floating water fern, one of the UK’s most invasive non-native aquatic species; proscribed under Schedule 9 of the Wildlife and Countryside Act 1981 (as amended)
The plant which forms a thick and dense mat over the surface of a pond preventing sunlight reaching the water depletes oxygen resulting in a catastrophic loss of native diversity. Spreading extremely easily through the transference of organic material, the fragmented nature of the plant means that minute pieces can easily regenerate and be transported between water courses, inadvertently on boots, on fishing or pond dipping equipment, dogs and perhaps most hard to control – wildfowl.
Like all ferns, in autumn the plant releases thousands of spores, meaning transmission of the species is almost impossible to prevent within the immediate vicinity.
Mechanical control is often equally damaging to the biodiversity of the pond. Ebsford had recently completed the restoration of Stumps Hill Pond, reinstated new banksand introduced new aquatic planting, so we were very keen to limit any damage. The use of Glyphosate based chemicals can be employed for control, however there is increasing demand to limit the use of chemicals within sensitive and public locations.
Ebsford were invited back to the pond to help and quickly ascertained it was extremely serious problem for the biodiversity. A dense mat of azolla covered the entire surface of the water and had started to terrestrialise the marginal damp areas of our newly created pond edges.
Within the wider Beckenham Place Park, there is an extensive new lake complex which it was extremely important to try and keep azolla free. Ebsford proposed a solution with a difference to manage the weed naturally. A seed population of the North American weevil Stenopelmus rufinasus acts as a Bio Control agent.
The weevil relies exclusively on Azolla as a food source and are host specific, meaning their introductionis completely safe and bio secure – posing no risk to native ecosystems. As the Weevil population explodes the weed is depleted and due to its long occupancy, the weevil is considered by DEFRA to be ordinarily resident and therefore no licensing was required.
With the help of local volunteers, Ebsford released a staggered seed weevil population into the pond in July 2020, over a period of 4 weeks. By week 2 a significant reduction in both density and extent of the mat could be seen, with clear water starting to show. Within 8 weeks the Azolla was almost completely gone from the surface of the pond with clear open water visible.
