Azolla is sometimes confused with duckweed and will cause similar problems in ponds. Here’s some information to help identify and treat this equally invasive pond weed.
Azolla (Azolla filiculoides), or fairy fern, is an attractive weed with fern-like fronds which turn a reddish colour in autumn. However, it is extremely invasive and was banned from sale in 2014. Once introduced to a garden pond, lake, or our wider waterways, it can spread rapidly forming a thick mat which blocks out light and reduces oxygen availability – as well as giving the appearance of a solid surface which animals, or children, may mistake for dry land.
The only solution currently for dealing with Azolla problems in ponds is a weevil which is available from the agricultural research organisation CABI via their website. You can find more images to help with identification and information on purchasing weevils at https://www.cabi.org/what-we-do/cabi-centres/azolla-control/
The weed just visible on the iris in our photograph is duckweed (Lemna minor). This can develop in the same way as Azolla causing similar problems but can be treated with Ecopond Duckweed Control which will, with regular dosing, prevent re-growth and spread. For more information on preventing and treating Duckweed see our separate Duckweed information page.
