Chelsea 2017: Taming Invasive Plants

May 25th, 2017 | Plant Talk with Graham Rice | 0 Comments

Japanese Knotweed (Fallopia japonica) smothering a building.

Japanese knotweed (Fallopia japonica) is a terrifying plant. Its presence in your garden will reduce the value of your property, lenders may refuse a mortgage and, if you have it, you’re required to tell potential buyers. The  Environment Agency describes it as “indisputably the UK’s most aggressive, destructive and invasive plant”. And, of course, it smothers native wildflowers.

In its instructive, rather chilling – and very popular – Chelsea exhibit entitled Finding Natural Solutions to Invasive Plant problems, the Centre for Agriculture and Biosciences International (CABI) shows how they’re getting away from simply spraying invasives with weedkiller – usually more effective on nearby wildflowers than invasives – and exploring natural solutions.

Japanese knotweed is the worst invasive plant we have; walls, floors, drains and foundations – nothing stands in its way. But the exhibit reveals that a sap-sucking, aphid-like insect from Japan, a psyllid that kills knotweed, may be the answer.

“The first insects were released in 2010 but the first release didn’t go well,” Dr Dick Shaw, Country Director UK for CABI, told me. “They’d been bred in the lab for 140 generations and were not as effective as we’d liked. Now we’ve secured new stocks from high altitude in Japan and we’re very confident they will do the job.” They will not attack related plants in our gardens or in the countryside; the closely related Russian vine, also known as the mile-a-minute vine, is not affected.

Dr Shaw and CABI are also working on other natural ways of eliminating invasive plants including a type of rust fungus that attacks Himalayan balsam. There’s also a fungus to kill the stumps of buddleja after the top growth has been cut off; buddleja is an increasingly troublesome plant that can obscure signals along railways. A similar treatment for invasive rhododendrons is being investigated.

It’s heartening that we’ll soon be able to deal with these worst of invasives in a natural way and without covering our gardens and countryside with weedkiller.

Sap sucking psyllid versus Japanese Knotweed

* CABI works around the world, in particular helping farmers in less developed countries combat invasives of all kinds that affect their crops. This short video explains how.

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Is one of our best known gardening writers. A graduate of the Royal Botanic Gardens, Kew, Graham was previously Gardening Correspondent of The Observer.
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