I think you are talking about Stitchwart rather than Starwort. 

It will be difficult to get rid of this. This year it is thriving because of all the wet weather we have been having. If it is in your garden, pull it and at least try to cut it back before it goes to seed. It is a perennial so any you don’t remove will be back next years just like dandelions. 

You could also spot spray them with an herbicide but we don;t really recommend that. If you choose to go this route, be sure to read the label, follow instructions and wear protective closing. Do not spray on windy days or then the temps are above 80°.

https://www.minnesotawildflowers.info/flower/lesser-stitchwort