Tag Archives: INNS Must Out

Floating Pennywort on the Wandle

Alan Martin, our Invasive Non-Native Species Officer, has been very busy this last growing season. Working with our trained River Rangers to map all invasive plants on the Wandle, and with the newly trained Hit Squad to start controlling them, we are making great progress.

One species we’ve had some great success with is floating pennywort. This aquatic invasive plant can be found along the river from Carshalton to Wandworth. Alan has developed and implemented a combined manual and chemical approach to tackle this species from its source in Sutton, and work until it is out of the river in Wandsworth. While this is going swimmingly, he has also looked at two sites on the Wandle where pennywort has a stronghold: Watermeads and Ravensbury Park.

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At Watermeads, the floating pennywort had infested a large backwater, a potentially key habitat for river wildlife with added aesthetic, recreational and ecological benefits. Working with the National Trust, Alan set to develop a management regime for this habitat to maintain it as an open water and keep pennywort at bay.

So how did we do it?

Manual Removal

To reduce overall biomass, several hand pulling events were held with volunteers from the National Trust and Wandle Trust – you may recall the epic Battle of Watermeads? Rafts of pennywort were cut away and towed to the bank using long grapple lines. The pennywort was then wheelbarrowed to a site away from the river where it would be left undisturbed to rot away.

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Foliar spraying

After reducing the initial biomass, herbicide was then used on the regrowth. With Environment Agency permission, Alan and Richard (from the National Trust) applied the first spray of herbicide in February this year.

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With this combined approach, open water was achieved!

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Continued monitoring

The secret to this work is that the work actually never stops. As long as there is a source of pennyworth on the Wandle, there is a risk the backwater could become re-infested. The local angling club at Watermeads and the National Trust volunteers have taken ownership of this site and continue to check for signs of pennywort, pulling out new plants. By keeping on top of it this way, it should never reach the scale it was back in 2015.

So what’s next?

Working with Merton Council and the Friends of Ravensbury Park, we are starting a similar management plan on the lake in Ravensbury Park which has been full of pennywort for years. Watch this space!

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