Action: Water primrose: Combination treatment using herbicides and physical removal
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- A study in California, USA1, found that application of glyphosate and a surface active agent called Cygnet-Plus followed by removal by mechanical means achieved a 75% kill rate of water primrose.
- A study in Australia2, found that a combination of herbicide application, physical removal, and other actions such as promotion of native plants and mulching, reduced the coverage of Peruvian primrose-willow by 85-90%.
A combination treatment of herbicide application and physical removal offers a tool for localised population reduction, and can be used to prevent significant deoxygenation of the water body due to decomposition of treated plant material.
Numerous attempts to eradicate water primrose report that a combination treatment is much more effective than chemical treatment alone. For example, a study in the USA reported that mechanical removal alone had limited effectiveness, whereas a combined glyphosate spray/mechanical removal treatment, though most expensive, gave the most lasting control of water primrose Ludwigia spp. (San Francisco Estuary Institute, et al. 2004). In support of this, it is reported that large-flower primrose-willow Ludwigia grandiflora was controlled in the Marais Poitevin, France by regular management actions including both mechanical and chemical methods (EPPO 2011). In addition, it is reported that after a single application of 4.3 kgs glyphosate/ha a population of water primrose Ludwigia spp. almost returned to its initial invasion stage after two years (Dutartre & Oyarzabal 1993; Delbart et al. 2013).
San Francisco Estuary Institute (2004) Field evaluations of alternative pest control operations in California waters. San Francisco Estuary Institute, Oakland, California. 107pp.
European and Mediterranean Plant Protection Organization (2011) Pest risk assessment for Ludwigia grandiflora. European and Mediterranean Plant Protection Organization, Report number 11-16827. 46pp.
Dutartre, A. & Oyarzabal, J. (1993) Gestion des plantes aquatiques dans les lacs et les étangs landais. Hydroécologie Appliquée, 5, 43-60.
Supporting evidence from individual studies
A study in 2005 in the Laguna de Santa Rosa, California (Sears et al. 2006) found that application of glyphosate and a surface active agent called Cygnet-Plus followed by removal by mechanical means resulted in a 75% kill rate of a long-standing population of water primrose Ludwigia spp. and removal of 5,388 tonnes of water primrose plants. However, in some areas of incomplete kill, there was rapid regrowth. Following the eradication attempt, there was heightened turbidity. However, intensive water quality monitoring revealed very low levels of glyphosate and associated metabolites. The herbicide was applied in July 2005 from the bank, using spray hoses located on the back of specialised vehicles. It was therefore necessary to drive over water primrose located in the flooded wetland, thereby covering some with muddy water prior to spraying. Channel areas (47 hectares) were sprayed from shore. Quantitative and qualitative vegetation monitoring were carried out before and during the project.
A study in 1996-2001 in the Botany Wetlands, Australia (Chandrasena et al. 2002) found that using a combination of herbicide application and physical removal, and other actions such as promotion of native plants and mulching, reduced the infestation of Peruvian primrose-willow Ludwigia peruviana by 85-90%. The cover of indigenous perennial plants increased. This was facilitated by ‘capping’ select areas of slushy mud with additional soil suitable for plant growth. Herbicide application on single-species stands was based on 1.0% ‘Bi-active’ glyphosate, but for mixed stands containing desirable plants 0.6% 2,4-D amine was applied. Each year, dead weed stands were mechanically cleared and burned to remove risk of regrowth. To control Peruvian primrose-willow seedling flushes, leaf and bark mulch was added to areas cleared of water primrose, and the water level of upstream ponds was managed.
- Sears A.L.W., Meisler J. & Verdone L.N. (2006) Invasive Ludwigia management plan. . Sonoma State University and Marin/Sonoma Mosquito and Vector Control District, Sonoma, California, 1-25
- Chandrasena N., Pinto L. & Sim R. (2002) Reclaiming Botany Wetlands, Sydney through integrated management of Ludwigia peruviana and other weeds. Proceedings of the Thirteenth Australian Weeds Conference, 134-137