Pennywort – spot the river

The Environment Agency has just announced funding of £20,000 to help control Floating Pennywort, an extremely fast growing aquatic plant on the River Soar around the City of Leicester.

It first appeared on the Soar upstream of Leicester in 2004 and during 2005 spread extensively – choking the river and its tributaries within the city. Leicester City Council worked hard with volunteers to remove the invasive species by hand, but by 2006 Floating Pennywort had spread extensively downstream from Leicester, with a large growth spurt in autumn 2006.

This is only the third Floating Pennywort outbreak ever targeted with funding, with the others being in Devon and the East Anglian region. Half of the £20,000 funding will go to Leicester City Council and half to British Waterways.

Environment Agency Midlands ecologist Phil Harding said: “Floating Pennywort was the one invasive species we really didn’t want to get. It’s quite an awesome plant which can grow 20cm a day.”

More details in the current NAFAC Summer 2007 Newsletter (eNewsletter version also available for download by members from the NAFAC website)

The preferred approach to managing floating pennywort is to manually remove the weed and possibly use a herbicide.

“Unfortunately I don’t think it’s possible to totally eradicate the species using these methods, we can simply manage the problem.”

But work now being carried out at the Centre for Ecology and Hydrology using a biological control shows promising signs.

An initial study of the Argentinean weevil Listronotus elongatus shows the insect specifically eats floating pennywort and vitally, completes its entire lifecycle on the species.

Head Aquatic Plant Management Group, Jonathan Newman, said both the larvae and adult form of the species consume the weed, which then dries out and dies.

“The two main things that you look for in a biological control is that the species completes its entire lifecycle on the invasive weed and won’t eat other native species,” Dr Newman said.

“There is still work to be carried out on a number of native plants, but the results so far are promising.”

Floating Pennywort Facts
Background: Originally from North America and was brought to Britain in the 1980s as a plant for tropical aquaria and garden ponds. However by 1991 it had become present in the wild.

Problem: Grows in shallow, slow-flowing eutrophic water bodies, floating pennywort forms dense interwoven mats of vegetation that extend up to 40cm above the water surface and up to 50cm below. These mats quickly cover the water surface and can grow 20cm per day, starving the waterbody of light, nutrients and oxygen which kills many of the species living in it and also increases the risk of flooding by blocking the waterway.

Physical description: Has circular or kidney-shaped, deeply lobed leaves, up to 180mm across. The stem is horizontal with a fleshy appearance and has leaf stalks and roots every 0.2-0.3m. It has no flowers and can double its weight in as little as 3 days.

Where found: Relatively restricted to about 35 sites in the south of England and south Wales. It is very likely to spread around UK watercourses and become a major nuisance in the future.

Treatment: Manual removal plus use a herbicide containing Glyphosphate or 2,4-D amine, followed by cutting and removing the weed 2-3 weeks later. Very difficult to control due to its rapid growth rates. The use of an approved herbicide in or near water requires the prior written approval of the Environment Agency.

Stopping the invasion of non-native species

The Environment Agency is joining a coalition of government bodies aiming to protect UK plants and animals from invasive species such as Floating Pennywort in Leicester.

Consultation to refine the Governments Invasive Non-Native Species Framework Strategy will focus on stopping further incursions from non-native species and limiting any negative impact from those already established, by:
Prevention: to reduce the risk of invasive non-native species being introduced;
Early detection, surveillance and monitoring: ensuring effective mechanisms are developed so that invasive threats can be responded to quickly;
Control and eradication: finding the best solution and identifying the right approach in the case of each species;
Raising awareness: ensuring that the public is aware of invasive non-native issues;  
Research: ensuring that there is up to date information on the threats posed by these species, and the best methods to tackle them.  Legislative framework: ensuring that current and any future legislation can adequately guard against the negative impacts;  Head of Conservation Paul Raven said the technical expertise of the Environment Agency in dealing with problems posed within river systems in particular, would play an important role in counteracting the impact of non-native species.

“The Environment Agency’s remit involves elements of detection, control, research and public awareness of non-native species that have already reached Britain, and it’s hoped this new framework will improve collaboration between organisations and individuals across the country,” said Dr Raven.

“While our main concern is the detrimental effect that non-native species can have on our native wildlife and habitats, some can also have an impact on agriculture, fisheries and flood risk management.

“We’ve identified 70 non-native species that hinder our work with 36 being a particular problem.”

Examples of current Invasive Species concerns for the Environment Agency include:
– potential flooding problems caused by floating pennywort clogging up drainage channels;
– river banks being undermined by signal crayfish and Chinese mitten crabs;
– increased flooding risk as a result of dense growth of Japanese knotweed along river banks;
– signal crayfish displacing and killing native crayfish by carrying a deadly fungal disease;
– topmouth gudgeon displacing native fish in lakes;
– changes in the biological make-up of rivers as new species invade;
– spread of Japanese knotweed as a result of disposal of soil as waste;
– the impact of mink on water vole numbers.

A recent study carried out in England has shown that there are 2,721 non-native species in England, of which 1,798 (66%) are plants.

Complete eradication is often too expensive and impractical. For example it has been estimated that it would cost £1.56billion to eradicate Japanese Knotweed (an invasive non-native weed) alone.