I've tried pulling up the foliage to weaken them. I've sprayed them with Glyposate but the only sure way of getting rid of them is to dig them out manually.

after flowering pull the dead flower out and spray with glyphosate so the weed killer is taken down into the bulb. over a couple of years hey do die.
or dig them out but i always find some are left behind in the ground.

Thanks everyone