Alien “nuisance” plant almost eradicated in the UK
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The Ludwigia grandiflora, or water primrose, has been almost eradicated in the UK.
L. grandiflora, which is currently unmanageable in France, is an aquatic plant native to South America. It can spread rapidly and presents a threat to many aquatic species. The very dense mats it forms can deprive the submerged plants below of light, cause problems for associated aquatic invertebrates, clog up waterways and exacerbate flooding risks.
Amongst the main species likely to be affected are fish. L. grandiflora can lead to more algal growth in more static water and invade the space needed by fish to survive. It could also provide perches for cormorants and herons, leading to increased predation.
Some non-native aquatic plant species, mainly introduced in the UK for horticultural purposes, have become established in the wild where they are becoming more widespread through vigorous growth. Many are popular with gardeners; but when they get a foothold outside the confines of gardens, there are no natural controls to keep them in check. For some, climate change may act in their favour: warmer winters might contribute to their establishment by allowing greater time for prolonged growth periods.
Ludwigia is an invasive non-native species and can double its biomass every 40 days in summer. Studies done in France have shown that Ludwigia species were able to double their biomass in 15 to 20 days in some waters.
A trial of methods to eradicate the weed started on 1 September 2006. Defra commissioned the Centre for Ecology and Hydrology to do the work (the Environment Agency is also helping). Since the work started there has been considerable success with destroying the plant. The treated sites are being monitored to ensure there is no re-growth but the signs are that as the trial continues the “problem” is diminishing and complete eradication may well be feasible.
Ludwigia is sold mainly in the more specialist garden centres, but trade in this species has been increasing in the last decade. It isn’t covered by the Wildlife and Countryside Act (1981) at present, so it is not illegal to allow the spread of this plant in the wild. However Defra will be reviewing this in 2007.
The main detrimental impacts of Ludwigia are:
- blocking of canals
- invasion of shallow lakes
- increased sedimentation leading to shallowing of waterbodies and increased flooding
- Reduction of flow in channels leading to flooding
- a reduction in submerged plants leading to problems of deoxygenation and consequent fish deaths
- loss of open water habitat
- loss of bare mud habitat
- interruption to navigation
- woody debris does not rot down and therefore clogs waterbodies, providing substrate for filamentous algae growth
- create static water which can provide breeding grounds for mosquitoes
Further information
See Eradication strategies for invasive non-native Ludwigia species (PH0422) on the Defra Science website.
Page published: 02 January 2007