Getting swamped: Australian swamp stonecrop (Crassula helmsii) in the UK

In January this year, large parts of southern Australia were ablaze with fierce bush fires, while most of the UK was covered in snow. Half a world away from each other, and at one point nearly 40ºC apart, there aren’t too many similarities to be drawn between the two locations. And yet, there is a water weed, Crassula helmsii, that survives happily in both extremes – and in the UK, where it has been introduced, this adaptability is proving extremely problematic.

 Crassula helmsii, also known as Australian swamp stonecrop or New Zealand pygmyweed, is a small semi-aquatic plant in the Crassulaceae family. As its common name implies, this low-growing succulent originates from the antipodes, but was introduced to Britain from Tasmania almost 100 years ago. Initially sold by garden and aquatic centres as an oxygenating plant, by the 1950s it had established in the wild, and from there it has spread to numerous ponds, lakes and waterways throughout the UK.

A mat of Crassula helmsii in flower

A mat of Crassula helmsii in flower

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Biological control of Mikania micrantha: Have we found the silver bullet?

Mikania micrantha (mile-a-minute weed or South American Climber) is a major invasive alien weed in many of the tropical moist forest regions of Asia.  This neotropical vine is able to smother plants in agricultural ecosystems, agroforestry and native habitats.  Conventional control methods of manual removal (slashing) or herbicide application, are expensive, ineffective, not sustainable, and can be environmentally damaging.  Classical biological control was considered the best option to manage this weed, and CABI was funded by DIFID (UK- Department for International Development) to implement this strategy in India.  The research culminated in the release of a coevolved, host specific, rust pathogen (Puccinia spegazzinii), from the South America native range of the weed, into Kerala and Assam.  This rust pathogen infects all aerial parts of the plant (leaf, petiole and stem), leading to cankering and whole plant death (see image below).

Puccinia spegazzinii Nov 10

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Our rivers – corridors for colonisation

Our river systems are undoubtedly one of the most diverse habitats found within the British Isles.  They provide us with numerous benefits including areas for relaxation and recreation, they harbour high levels of biological diversity, act as natural flood management, provide water for consumption and irrigation, and act as corridors for the movement of nutrients and species in an otherwise fragmented landscape.  However, our river systems are highly vulnerable habitats.  Seasonal variations in hydrological processes render riparian habitats prone to high levels of disturbance which aid the invasion and colonisation of invasive plant species.

RT.13.5.06.Devon.site.5 (5) Himalayan balsam monoculture on the banks of the River Torridge, North Devon, UK (CABI)

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Can biocontrol bash the balsam?

After a long hot summer, many custodians of the countryside will be breathing a sigh of relief as the winter months will provide a rest bite from battling with infestations of non-native plant species.  Unfortunately, the battle is too often one sided and the weeds are winning!  Himalayan balsam (Impatiens glandulifera) is one of the UK’s most invasive non-native plant species and an incredibly difficult plant to control, due mainly to the inaccessible and sensitive habitats where it grows.  As a weed of riparian habitats chemical control is often not a viable option, manual control is labour intensive, and for any control effort to be successful control must take place on a catchment scale else seeds from populations upstream will colonise cleared areas during the late summer months.

RT.Devon.2008.Aug (16)

Himalayan balsam invading pasture-land in the Camel Catchment, Cornwall, UK (CABI)

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