Like all plants Bishop's weed (also called Gout weed, Snow on the Mountain and Aegopodium ) needs sunlight to survive so covering the plant with plastic or cardboard or cutting it to the ground every week for a few months will starve out the roots. If you want fast results using RoundUp is effective and kills the roots and all. If you need exercise dig out the plant roots and all looking for every bit of root and tuber to rid the area of this overly ambitious plant. Keep growing - but careful what you grow, Marianne Binetti