So what's the problem?
Crassula helmsii (also known as New Zealand Pigmyweed or Australian swamp stonecrop owing to its area of origin) is an invasive water-weed which is spreading rapidly across the UK. It was introduced from the antipodes in 1911, and it has since flourished. It invades still or slow flowing water bodies, excluding most other flora and fauna and forming a virtual carpet.
The EU Water Framework Directive aims to protect and restore clean water across Europe and ensure its long-term, sustainable use. The UK Government is responsible for all rivers in the UK, and it needs to ensure they’re clean and weed-free by using environmentally friendly and economic solutions.
As Crassula has gone past any containment or eradication stages, the government needs to try controlling in a way without chemicals that would make the water toxic.
What is this project doing?
CABI was commissioned to investigate the potential of finding a biological control (or biocontrol) for Crassula helmsii.
To do this, the CABI team visited the weed’s native range (in Australia and New Zealand) to see what natural enemies (either insects or fungal) are attacking the plant and keeping it in check. We both collected and identified any damaging natural enemies, in order to export them to the UK and assess their suitability.
Together with the Department of Primary Industries, Victoria and the University of Tasmania, surveys to Victoria and Tasmania in Australia are taking place to find natural enemies in the native range throughout the seasons. Natural enemies, potentially new to science, have already been exported to CABI's quarantine facility, and are being formally identified. We are also researching their life history to gain a greater understanding of these species.
Following this, the team performed what is known as host range testing – to ensure the selected natural enemies don’t attack any native flora – against a drawn-up list of non-target plants.
Results so far
Recent surveys conducted in Victoria and Tasmania in Australia resulted in the discovery of a range of natural enemies that caused significant damage to this destructive water-weed. This is particularly encouraging as up to now, no organisms have been recorded using this plant as a resource in Crassula’s native range. Several plant pathogens which cause damage to the leaves have been observed as well as stem mining insects. This is particularly positive with unusual rainfall restricting survey possibilities. These fungi and insects have been exported to CABI’s quarantine facility in Egham in the UK to formally identify and conduct life history studies. Early investigations have produced promising results.
A list of 59 plants has been produced which are related to, share a habitat with, or are morphologically similar to Crassula helmsii in the UK. These plants will be tested for susceptibility against any potential biocontrol agents that attack Crassula. The list includes species protected under the Wildlife and Countryside Act and several economically important plant species. Surveys will continue during all seasons to cover a greater area and to ensure no important organisms have been overlooked. The initial findings of the first phase present a promising start to the project with exciting opportunities for the future.
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