Unfortunately the only herbicides that effectively control locoweeds are restricted use herbicides. You can contact a local landscaping or weed management company and ask to use: Grazon P&D, Escort, Ally or Clopyralid) when plants are actively growing and when enough soil moisture is present to achieve full and fast control of locoweeds. 

After spraying, reducing grazing pressure and encouraging desirable vegetation is key. 

Pulling or digging plants out frequently should also kill them eventually. Make sure to dispose plant parts, and especially seeds away from the field.