Invasive Species Week: Non-native species which has to be kept under control


This Invasive Species Week, we're spreading the word about different invasive species we often come across. Himalayan Balsam, Giant Hogweed, Japanese Knotweed and Crassula Helmsii can be a problem on our water and wastewater sites, so we want to understand more about them and how to practice biosecurity. That means taking precautions to prevent the spread of any unwanted INSS.

So, we have a training programme in place and have committed to increasing our knowledge of INNS. This is all part of how we want to help protect our water loving native species and the precious environment around them. 

Crassula Helmsii - just one of the invasive species we find on our sites

When the Crassula Helmsii plant finds a place it likes, it grows across large areas forming a thick mat of stems and leaves.

This can be a problem when it grows on the filter beds of a wastewater treatment works, because it can stop the filter arms from turning properly. The filter is important for treating wastewater correctly, but this is where Crassula enjoys the damp and light environment that the equipment provides. Having such dense plant growth can also affect our native species which live in and around the water, as their light and oxygen diminishes with the increasing blanket of plant growth covering it. Crassula is an invasive non-native species (INNS) that we could do without.

Tackling Crassula with innovative techniques

It’s really difficult to eradicate this species of plant, so we need to keep it under control on our sites. We already make sure that operators at sites which have Crassula on filter beds check, clean and dry their clothes and equipment, to stop them spreading it to other sites. But we’re doing something more innovative too, to help reduce the amount of plant material created by this successful plant invader. Since 2019, we’ve been working with the Centre for Agriculture and Bioscience International (CABI) on a special project to find a new biocontrol – a microscopic mite that reduces plant growth.

A mite which might work – early signs are promising

Following successful laboratory trials, Crassula was collected from our Bewl Water reservoir and infected with the mite, before reintroducing it back to the reservoir in the summer of 2020. The mites are successfully surviving our darker and colder winter months – this the best performing field site of the trial - and this spring it looks as though they’re laying eggs. All the signs are encouraging, and as laboratory tests found that the mite could reduce plant growth by up to 50%, we’ll just have to wait and see what happens in the real world.

Managing INSSs as part of our commitment to protect and enhance the environment