On 02/11/2020 19:45, Adrian Brentnall wrote:

I try not to use weedkillers in the (vegetable) polytunnel - but
'organic' techniques (like vinegar) offer only a temporary respite.

I'm guessing that something systemic is required.
Recommendations, please?

Digging it out with a fork usually works OK for me on a heavy clay soil.
It isn't all that invasive and relatively shallow rooted.

It puts up less resistance to a fork than nettles. I have snapped fork
tines on overgrown combinations of bramble, nettle and honeysuckle.

Only for ground elder do I resort to chemical warfare prior to digging.
Since that has a tendency to come back from every tiny piece you miss.

--
Regards,
Martin Brown