Dead and gone: Steam exposure kills layered clumps of invasive curly waterweed Lagarosiphon major

Population suppression and eradication of invasive, alien macrophytes can be complex, costly and labour intensive, therefore prevention of further spread is an essential aspect of management. However, following the physical removal of entangled clumps of plant material adhering to anthropogenic vectors including outboard engines, guidelines for appropriate disposal are often unclear, inadequate, or non-existent. Here, we explore use of direct steam exposure to cause complete degradation of layered clumps of invasive curly waterweed Lagarosiphon major (Ridley) Moss. Clumps were arranged as three, stacked 15 × 15 cm layers, with 40 ± 0.1 g of entangled stems per layer, to which steam was directly applied downwards onto the top layer. The top surface area was divided into nine subsections to ensure an even application of steam per 5 × 5 cm for durations of 5, 10, 30, 60, or 120-sec, equivalent to 0.75, 1.5, 4.5, 9, or 18-min steam applications. Ten seconds of exposure caused total degradation of top and middle layers, while up to 30-sec was required for the bottom layer. For shorter exposures, new growth - if it occurred - was evidenced by a single new shoot of <5 mm in length following 28-days of recovery. Conversely, control specimens displayed excellent survival and production of new growth. We suggest that the simple, yet highly efficacious technique of steam exposure can be used to improve prevent spread of invasive macrophytes.