Having been a keen amateur botanist all of my adult life, my love of the wildflowers of watersides and wetlands led to the publication, in 2005 and 2006, of a book series Wonderful Wildflowers of Wales, which I co-authored. Volume 4 in the series is dedicated to in-stream and marginal wildflowers. For this reason, if none other, I share the concerns of many at the spread of alien plants and their devastating effects on much of our countryside. The control and where possible eradication of invasive alien plants is therefore something that I am very keen to contribute to.

Very many exotic (imported) plants have escaped or been thrown out from gardens, and some have been more successful than others in the wild. Top of my list of riverside 'baddies' would be Himalayan Balsam (Impatiens glandulifera), Japanese Knotweed (Fallopia japonica), Giant Hogweed (Heracleum mantegazzianum), and Rhododendron (Rhododendron ponticum). Various imported pondweeds including Canadian Pondweed (Elodea canadensis), Australian Swamp Stonecrop (Crassula helmsii), Parrot’s feather (Myriophyllum aquaticum) and Floating pennywort (Hydrocotyle ranunculoides) are now causing serious problems in natural ponds, lakes, canals, slow-flowing streams and drainage channels.

They are attractive, it's true. That's why they were introduced into this country, of course. The problems are many and various. From a conservation point of view the most seriously invasive aliens crowd out our indigenous wildflowers. For example, Himalayan Balsam can easily eradicate such native gems as Purple Loosestrife and Water Mint.

Blocking drainage channels and adding to flood risk is another problem, as indeed is the riverbank erosion that occurs when deeper-rooted perennials are replaced by alien annuals that die back in winter to leave the soil completely exposed.

For some plants - Himalayan Balsam, for instance - this can help control the growth on riverbanks and might even eradicate the species from small isolated ponds. But if say Japanese Knotweed were treated in this way the fragments of root left behind could each produce a new plant - the opposite to the desired effect.

Chemical controls work on some species, but chemicals must never be used near rivers or lakes without the approval of the Environment Agency. The Agency publishes guidance on invasive and aquatic weed control, and here are links to summary notes available via the Environment Agency's website:

• Japanese Knotweed
• Giant Hogweed
• Himalayan Balsam
• Parrot's Feather
• Australian Swamp Stonecrop
• Floating Pennywort