Why not mix some Glyphosate with wallpaper paste and you will be able to paint it on the bindweed? You could also cut the bottom out of a plastic bottle, place it over the weed and spray through the top.

Can you cover the surrounding plants with plastic sheeting or old newspaper or something to prevent the spray landing on wanted plants? Or you could surround the cane loosely with plastic to form a wide cylinder and direct the spray down inside it? I've done this successfully. Works well if you are careful. This is if the plant is too big for Jimmy's suggestion - same principle though. Choose a day without wind.

Thanks for your suggestions, will try to do it next week, after my plant sale.

I use a plastic 2 or 4 pt milk bottle and cut the bottom off and the top only if necessary place this over plant I wish to kill and spay down the inside. You could move it up post from bottom to top spraying as you go down the bottle. I have done this with mares tail.

Oooh. Jennh! Did it work on mare's tail??

Do not want to speak too soon but mares tail started to come from next door after owner died and left empty for a while.as soon as I saw some put bottle over it top side into earth and sprayed a few times each one has gone but I think I will always have some now, I trim each side of mares tale so plenty of cut surfaces .

Just as an aside, mares tail has a silica coating so it might need to be crushed as some weedkillers do not dissolve the coating. I would also leave the fronds as they are so they will take up the maximum amount of weedkiller.