Sacha wrote:

It's a translocated weedkiller, which means the weed has to be in
active growth to move the chemical from where it makes contact (the
leaves) to where it takes effect (the roots). Applying it in the dark
rainy cold days of November is a waste of money.

Thanks for the warning.
I should have said that the garden in question is in Italy,
and there were a few very sunny days after I applied the roundup.
But I'll read the label as you suggest before applying it next time.

Saying where your garden is is of the utmost importance. I know I go
on and on about this but really, how can anyone advise anyone else if
they don't know where they're gardening? Is there an Italian gardening
group which would help you with queries like this?

I'm sure there is.
The Italians strike me as even more fanatical about gardening
than the English.
Actually, I haven't seen Roundup sold in Italy.
Certainly the local garden centre (quite large) doesn't stock it.
I asked last week for "Feed and Weed" there for our little patch of grass,
but the expert refused to sell it to me as he said it was much too late
in the year and would be a waste of money.

And even then, which part of Italy? Piemonte or Apulia?

It's in eastern Tuscany, near Umbria.
It's quite cold now, and there has been a huge amount of rain
in the last week.
Someone told me the annual rainfall here is higher than in Dublin,
where I live. The difference is that it is spread over the whole year
in Ireland, while here it is concentrated in torrential downpours.