Crassula helmsii is listed on Schedule 9 of the Wildlife and Countryside Act in England and Wales therefore, it is also an offence to plant or otherwise cause to grow these species in the wild.
Mechanical control is difficult and usually not recommended as it can result in small fragments being left in the water, which may spread the plant downstream. Fragments as small as one node (5mm) can regrow. However, the risk of spread can be reduced by the use of a fence of fine wire mesh (5 mm) to enclose the area to be treated.
Shading out with dark-plastic sheeting has been successful with black polythene covering the plant for at least three months during the growing season, although this will have adverse effects on other species covered up. Shade materials may be laborious to install and move on a regular basis; vandalism may also be a problem at sites open to the public.
C. helmsii is susceptible to formulations containing glyphosate. However these applications must be made by a certified operator and Environment Agency consent is required for any herbicide use in or near water bodies. If the site is in or near a conservation site, such as, a Site of Special Scientific Interest, then the control strategy must be discussed with the local Natural England office.
Manual removal by hand allows selective removal of plants when C. helmsii is in the early stages of invading a diverse plant community but it is difficult and very laborious to be effective. Removed plant material should not be taken away from the site but should be stacked and composted under a secured light-proof cover, such as a thick sheeting and/or 0.2 m of soil. Machinery, boots and equipment should be thoroughly cleaned before leaving each site.
You should record the presence of invasive species on a national database. You can record online at the Non-native Species Secretariat website. You should also alert the appropriate land owner, council and or management body to the presence and location of this plant.