If it's green use Round-up, a none selective and biograde that doesn't effect the soil when it hits it. I wiped out a huge patch of lily of the valley. Use with caution. If the wind blows it anything green is dead. I had over spray that killed my lawn and some near by perennials. I then used a cardboard box open at both ends and tediously sprayed each section. No more lily of the valley. There is also a product called Wipe-Out. It can't grow if it has no sunlight if you go organic. Mulch doesn't work on bulbs unless the green is above ground. Hope that helps.