Best time to zap bindweed
 

We are trying to patch a 5 metre section of hedge destroyed during
re-building our house 2 years ago. The hedge we've planted is a mixture of
hawthorn, maple, beech and hornbeam against a field. The worst weeds being
goose-grass and bindweed. The whole bank is infested with it and it smothers
the hedglings. I've read that it's better to kill it later in the year
(around flowering time) rather than earlier on. Is this true? It's a devil
to unravel without breaking off hedge shoots.