Thank you for your question. Without seeing the flowers in bloom, I am assuming you are trying to control Virginia spiderwort, described here: https://cybercemetery.unt.edu/archive/allcollections/20090115191842/http://plants.usda.gov/plantguide/pdf/cs_trvi.pdf As that article indicates, the plant can be dug up manually and either divided and replanted, or disposed of. Because this species is a native, protected in some states, and sought out in nurseries, I can find no Extension research on controlling it. So, the only non-broadleaf chemical available (and no threat to native insects and animals) appears to be elbow grease. Good luck!