Biocontrol of escaped ornamentals

‘Plants that have escaped from gardens are invading wild habitats and are inevitable subjects for biological control’. CABI scientists Richard Shaw and Rob Tanner are interviewed by RHS’s ‘The Plantsman’ magazine.

As two of CABI’s invasive species specialists, whose work looks at controlling a wide range of invasive plants in the UK and elsewhere, including Japanese knotweed and Himalayan balsam, they met with the RHS to explain the problems associated with Invasive Alien Species (IAS) and the potential for classical biological control to mitigate the problems they cause.

Although only a small percentage of newly arrived plants escape and only 10% of these can establish and become invasive, plants have been brought to the UK for centuries and many species do not show their true invasive potential for decades after introduction.

Classical biological control – where natural enemies from the plant’s native range are reintroduced to it where it is invasive – can provide the answer. It has been used worldwide for more than a century and has now been used in an EU member state.

The article goes on to explain how biocontrol scientists firstly conduct primary research, which includes: identifying the weed’s area of origin, obtaining permissions and carrying out surveys throughout the plant’s growing season. S/He then move on to a testing phase, where they test morphologically and molecularly similar plants to see how any potential biological control agents affect them, then moving on to subtribe, tribe, subfamily, family and eventually including representatives from other orders. Any negative impacts mean that the potential agent is dropped from consideration.

Plants looked at in the article include Japanese knotweed (Fallopia japonica var. japonica), Himalayan balsam (Impatiens glandulifera), Australian swamp stonecrop (Crassula helmsii), floating pennywort (Hydrocotyle ranunculoides), giant knotweed (Heracleum mantegazzianum), water fern (Azolla filiculoides), Rhododendron and Buddleja.