Abstract
Non-native aquatic plant species are becoming more widespread and vigorous with time. This is partly due to selection by horticulturalists for vigorous plants, and possibly due to warmer winters allowing greater time for prolonged growth periods. The combination of more favourable climate and introduced species and hybrids has lead to the establishment of very vigorous non-native aquatic plant species, including Floating Pennywort (Hydrocotyle ranunculoides), Parrot`s Feather (Myriophyllum spicatum), Australian Swamp Stonecrop (Crassula helmsii) and Water Primrose (Ludwigia grandiflora). All these plants pose a very high risk to the integrity of UK aquatic ecosystems. The aim of any non-native invasive weed control programme should be eradication. For this reason we have selected Ludwigia grandiflora as the target species for assessment of the feasibility of eradication using herbicides. L. grandiflora is disjunctly distributed, indicating a human influence on dispersal and introduction. It is currently present in several different sites all of which are accessible and easy to manage using herbicides if approved. L. grandiflora exhibits very rapid growth rates, growing in water up to 3 m deep, reaching the surface and producing emergent shoots with large, showy yellow flowers about 1 m above the water surface. The rapid growth rates are responsible for complete coverage of a 500 ha shallow lake in the south west of France in under 6 years, a mean establishment rate over the 6 years of 83 hectares a year. These excessive growth rates are not yet observed in the UK, with dominance of only one site being reported to date. However, we expect to see such growth and establishment rates in the near future and we wish to demonstate how to eradicate this species rapidly to save millions of pounds in future control costs. We propose to compare the efficacy of a glyphosate based herbicide and a glyphosate and 2,4-D amine mixture based herbicide for the purpose of eradicating L. grandiflora from several sites. Glyphosate is a slow acting herbicide, is poorly translocated in rapidly growing plants, and kills many other non-target rooted species. The additon of 2,4-D amine to the mixture in this experiment is anticipated to enhance translocation rates of glyphosate through the plant, thereby improving long-term control. While glyphosate is excellent for control of many aquatic plant species, the use of glyphosate for eradication of non-native aquatic plants has proved challenging. This approach is novel and will contriibute to the management of such species if successful, and will also reduce pesticide use in the environment by improving efficacy of single applicartions. We aim to show that early intervention and eradication of a potentially threatening species can be successfully achieved by selection of the most appropriate method of control, without any adverse environmental impact.
United Kingdom