An Invading Plant

Early in March, I took a walk to Old Hall Copse at Woking Palace to see if the daffodils were in flower. They were indeed flowering and very beautiful. But then my companion asked "What's all that red over there?" I turned to look and knew the answer straight away, the Palace Moat had been invaded by the Fairy Fern also called Water Fern, Azolla filiculoides. This water plant turns bright red under environmental stress, it doesn't much like the cold and we'd had snow not long before.

Azolla filiculoides, March 2018

Oh no! Water Fern is a problem:
"Water fern can achieve 100% cover over the water surface as a carpet occasionally up to 30cm thick. At such times, it blocks out light, preventing photosynthesis in aquatic plants and preventing or compromising oxygen diffusion. It also prevents amphibians and invertebrates from reaching the surface and may disrupt movement of animals on the water surface" 

GB Non-Native Species Secretariat

This is a highly sensitive area, Woking Palace is a Scheduled Monument and Old Hall Copse is Ancient Woodland so a sensitive solution was called for. The best way was to introduce a North American,weevil, Stenopelmus rufinasus. These tiny creatures love eating Azolla, so much so that's all they do eat.

Stenopelmus rufinasus - Photo CABI

The introduction of the weevils took quite some time. A lengthy process since formal identification was needed, various permissions had to be sought and funding found after which the weevils had to be bred to order by scientists at CABI, the Centre for Agriculture and Bioscience International.
Eventually, the day came when the weevils were released. In July, assisted by the Chair of the Friends of Woking Palace the weevils were let loose to do their work. But there was a hitch. By the time the weevils arrived, the extremely hot, dry weather had dried up most of the moat and the Azolla along with it! Far less of a weevil feast than anticipated. Nevertheless, we hope that one way or another the fern will not make a reappearance in 2019.

If you'd like to see my detailed photo journal of the story of the Fairy Fern you can find it at: 
https://www.flickr.com/photos/37644698@N02/collections/72157698472118885/

You may also be interested to see:
NNSS Factsheet

CABI Azolla Control