If you can safely spray the leaves with roundup or preferably a stronger brush killer without contacting flowers and wanted plants it will kill it down,but remember that any part of the plant contains the oil irritant that has been tested after 100 years of drying and still causes reaction,like somebody said wear long sleeves and gloves and get rid of it before it seeds and spreads.Use throw away gloves if possible and don't wash the clothes with non-contaminated ones,they make several products that break the oil up.