Action: Water primrose: Physical removal
- A study in the USA found that hand pulling and raking water primrose failed to reduce its abundance, whereas hand-pulling from the margins of a pond eradicated a smaller population of water primrose.
Manual or mechanical removal of water primrose Ludwigia spp. with manual removal of any visible remaining fragments may offer a tool for localised population eradication.
However, it has been shown that water primrose demonstrates high regeneration capacity, and an ability to regenerate from small shoot fragments with a node with or without leaves (Hussner 2008). Therefore, it is important to carefully manage any mechanical removal program to prevent regenerative fragments from spreading to new locations.
Manual or mechanical removal programmes have been met with mixed success. For example, a review reports that effective management of large-flower primrose-willow Ludwigia grandiflora for eradication is relatively difficult, and mechanical removal tends to create viable fragments which can spread to new areas or recolonise existing managed sites (Plant Protection Service et al. 2011). A study found that mechanical harvesting, followed by several manual finishes over a two year period, eradicated large-flower primrose-willow. It was noted that ground realities, including inaccessible sites for heavy equipment, and difficulty observing the species, can strongly affect the feasibility (Legrand 2002). One study reported that in the early stages of water primrose Ludwigia spp. colonisation, removal by hand is usually possible, and that mechanised removal is only necessary when the plant has become well established (Thiébaut 2007).
Hussner, A. (2008) Ökologische und ökophysiologische Charakteristika aquatischer Neophyten in NordrheinWestfalen. Ph.D. Dissertation, Heinrich-Heine-Universität Düsseldorf, 192 pp.
Plant Protection Service, Plant Research International Wageningen UR, Aquatic Ecology and Water Quality Management Group & Centre for Ecology and Hydrology Wallingford (2011) EUPHRESCO DeCLAIM Final report A State of the art June 2011. Ludwigia grandiflora (Michx.) Greuter & Burdet. 63pp.
Legrand C., 2002. Guide technique : pour contrôler la prolifération des jussies (Ludwigia spp.) des zones humides méditerranéennes. Agence Méditerranéenne de l’Environnement, Montpellier, France. 68pp.
Thiébaut, G. (2007) Non-indigenous aquatic and semiaquatic plant species in France. In: Gherardi, F. (Ed.) Biological invaders in inland waters: profiles, distribution and threats. Springer, Dordrecht, pp. 209–229.
Supporting evidence from individual studies
A study in 2005 in a managed wetland in the Laguna de Santa Rosa, California, USA (Sears et al. 2006) found that hand pulling and raking water primrose Ludwigia sp. failed to reduce its abundance, whereas hand-pulling from the margins of a pond in the Laguna Wetland Preserve Sebastopol successfully eradicated a smaller population of water primrose. Attempts to reduce the coverage of primrose in the Laguna de Santa Rosa, California, were wholly unsuccessful and by the end of the season water primrose covered 100% of the pond. Hand pulling and raking were carried out for 2-6 person hours/week. Workers in the Laguna Wetland Preserve at Sebastopol spent approximately 150 person hours of effort hand-pulling water primrose from pond margins.