Water Primrose (Ludwigia peploides or grandiflora)
These species are aquatic plants that are native to South America. They have become established in parts of mainland Europe (notably France, Belgium and the Netherlands) where they are highly invasive and can cover large areas rapidly (e.g. 500ha. in 5 years in one area of France).
There are currently a small number of confirmed populations
in Britain (see map below). All are believed to be small and manageable but
they are likely to spread .
Map of confirmed Ludwigia populations
in Britain.
Impact
Ludwigia can spread rapidly and forms very dense mats which shade out plants that are lower in the water column. This, in turn, impacts negatively on aquatic invertebrates. The dense mats can also block waterways and degrade water quality. Studies done in France have shown that Ludwigia species were able to double their biomass in 15 to 20 days in some waters.
As with many aquatic weeds it can reproduce vegetatively by pieces breaking off plant parts as well as reproducing by seed. Like many aquatic plants early removal is essential to prevent spread through the watercourse.
Control
The main method of control is by using herbicides such as Glyphosate although care must be taken when using herbicides near water. The Environment Agency have produced a guidance booklet that is available here. Mechanical control (simply pulling the weed) is also possible but with both chemical and mechanical control great care must be taken to remove all the plant fragments as any remaining fragments will quickly regenerate.
Defra has recently funded a research project looking into the most effective ways of removing Ludwigia in Britain.
Links
CEH - Centre for Aquatic
Plant Management
Defra
- eradication strategy
Plant
Life - information sheet
Wildlife
Trust
Environment
Agency - Guidance on invasive weeds in or near water