Management of aquatic alligator weed (Alternanthera philoxeroides) in an early stage of invasion

Abstract

The presence of the North American Marmorkrebs (Procambarus fallax f. virginalis) in European inland waters is entirely driven by ongoing propagule pressure from the ornamental trade. Since 2003 at least 25 independent introduction events have been confirmed, of which some have eventually resulted in established populations. This study links a maximum-entropy model that forecasts the probability of Marmorkrebs introduction based on socioeconomic predictors to an updated species distribution model based on environmental predictors in order to explore the risk of further Marmorkrebs establishment in Europe. In line with related research, the probability of Marmorkrebs release was largely affected by gross domestic product and human population density, i.e. predictors very likely related to the density of Marmorkrebs owners, whereas environmental suitability was mostly influenced by minimum temperature and the availability of lentic habitats, which was indirectly assessed by terrain slope. While considerable parts of Europe were predicted as potentially suitable for establishment, high probabilities of introduction were forecasted in much smaller geographic areas. The consensus map of the model predictions suggests that introduction and subsequent establishment of Marmorkrebs is likely to occur in much of Germany, the Benelux countries, England, Italy, and areas of high human population density throughout France and Spain, as well as parts of southernmost Scandinavia and Southeastern Europe. Monitoring trades of Marmorkrebs in these high-risk regions is recommended and implications for proactive measures are discussed, including the need for consistent trade regulations at the EU level.

Herbicide efficacy for aquatic Alternanthera philoxeroides management in an early stage of invasion: integrating above‐ground biomass, below‐ground biomass and viable stem fragmentation

“…In contrast, in the small infestation experiment, there was about an 85% reduction in volume of turgid taproots, for glyphosate (IS), metsulfuron and imazapyr, although the biomass reduction was much less. These data indicate that effective control of below‐ground tap roots can be achieved utilising glyphosate when treating small infestations in an early stage of invasion (Clements et al ., ). Reduction in below‐ground biomass after herbicide application has been demonstrated in a limited number of mesocosm studies (Schooler et al ., ; Hofstra & Champion, ) and field studies (Bowmer et al ., ; Schooler et al ., ).…”

“…No benefit for control of aquatic A. philoxeroides , in an early stage of invasion, could be detected by adding surfactants to any herbicide treatment. These results were similar to previous findings where metsulfuron combined with the surfactant Pulse ® had no additional benefit (compared with metsulfuron alone) in controlling above‐ground aquatic A. philoxeroides (Clements et al ., ) or reducing viable stem fragment production (Dugdale et al ., ).…”

“…A visual estimate of A. philoxeroides per cent coverage within the potential total area, defined as the vertical projection of all plant material on the ground (or water's surface), within the ellipse was then made. Finally, potential total area and cover percentage were multiplied, and divided by 100, to give an estimate of the ‘area occupied’ by A. philoxeroides in each trough (Clements et al ., ). This process was then repeated for the ‘embankment area’ alone.…”

Alternanthera philoxeroides (Mart.) Griseb.

“…In the introduced range, A. philoxeroides is managed using both conventional (manual, mechanical and chemical control) and biological control (Sainty et al ., ; Clements et al ., ). Manual control, i.e.…”

“…Physical control is an approach to be used where chemical control is not deemed feasible, for example due to the sensitivity of the habitat (Clements et al ., ). In a study to evaluate the effectiveness of chemical and physical control methods on an early stage infestation, Clements (2014) showed that 75% of the population could be removed physically with minimal follow‐up treatments required to address any re‐growth.…”