On 16/09/2019 18:33, Martin Brown wrote:
On 16/09/2019 17:59, David Rance wrote:
On Mon, 16 Sep 2019 12:10:50 Nick Maclaren wrote:

In article ,
Martin BrownÂ* wrote:

Himalayan balsam is becoming quite a problem in North Yorkshire on
stream and river banks wiping out almost everything else and spreading
rapidly. Only Japanese knotweed out competes it. Nettles and rosebay
willow herb both die out after a few years leaving a monoculture.

I have never seen it do that, and I have been looking out for it for
several decades now.Â* I believe you that it is a (very) localised
problem, but it assuredly isn't a widespread one.Â* Every apparent

I can well believe that it is only a local difficulty, but it seems to
be incredibly effective at moving along water courses and colonising the
banks to the near exclusion of everything else unless treated promptly.
Its flowers smell quite nice in the evenings a bit like bizzy lizzies on
steroids the explosive seed capsules pack more of a punch.

monoculture of it I have looked at has turned out to be, on closer
inspection, merely that it dominates the top layer and there is a
wide range of other species underneath it.

Only if you count grasses which do seem to hang on in the margins.

Interesting about rosebay willowherb (or should it be rose bay willow
herb? - I've never been sure). I remember my father pointing out to me
the way that it colonised bomb sites during the second world war
especially in London. Then for most of my life it seemed to have
disappeared only to reappear in the last few years, and for the first
time I have some springing up in my garden.

I remember the rosebay willow herb of my youth being a much more
vigorous invasive weed in Manchester on a sandy soil. On my North
Yorkshire heavy clay it barely survives and is seldom seen in hedgerows
here except on or near railway enbankments.

Are there multiple sorts or is it very sensitive to local conditions?


The genus has 8 recognised species, but only one is in the British
Flora. (A second species occurs as a rare garden escape.) However in
North America at least there are two cytotypes (cryptic species) of
Chamaenerion angustifolium, with mostly disjunct distributions.
Supposedly it was a relatively rare plant prior to WWII, and became
somewhat invasive afterwards. I wonder whether a non-native strain was
introduced.

It's my 24th most recorded plant, coming in behind Dryopteris filix-mas
and Senecio vulgaris, and ahead of Epilobium hirsutum.