IT’S called Japanese Knotweed and its Latin name is Fallopia japonica, from its hollow stems, and it’s a very nasty invasive weed.

And every few months we have a mini debate about it in the House of Lords.

It grows to a height of ten or 15 feet when left unattended, in all kinds of places wet and dry. It grows up through cracks in pavements, undermines buildings and can even sprout through concrete.

It was brought from Japan to grow in gardens in the 19th Century.

It’s very hard to get rid of – repeated spraying by appropriate chemicals can take several years. Even small bits of the far-spreading roots (rhizomes) can sprout up again.

Lady Sharples and I tend to alternate with knotweed questions every few months, and last week was her turn. And we talked about a tiny Japanese insect called Aphalara itadori – a psyllid, or a jumping plant louse to you and me.

Laboratory trials have identified this little Japanese bug as just the job for keeping this alien superweed under control. It lives on it and eats it and it doesn’t eat anything else.

Or so they say. It’s now being tested at two carefully controlled sites in the wild for a period of five to ten years. If the trials are successful it may be let loose more widely.

Releasing alien predators to control other alien invaders is obviously something that has to be done with great care.

If we are not careful the answer to one problem might turn into an even bigger nightmare.

There was a classic case in Australia where cane toads were imported from Hawaii to control beetles that were eating sugar canes – only to turn into nasty invaders which poison other animals and even humans.

But our existing feeble efforts to control the knotweed cost over £150million a year – and the estimated cost of getting rid of it all (even if it were possible) was estimated a few years ago at £1.5billion.

If we move with care the jumping plant lice might work well.

The knotweed won’t disappear, but they might restrict its growth and make it easier to manage.

But I expect their Lordships will discuss it a few more times before we know the answers.