Black medic is normally a summer annual, but can act as a perennial in some conditions . It has a tap root, and spreads low to the ground, but it does not root from nodes on the stems. Black medic is more active on soils low in nitrogen fertility.
Good turf management practices, including a balanced nitrogen/phosphorus fertilization program, will encourage a dense stand of turf and make it difficult for black medic to persist. A nitrogen/phosphorus ratio of 2:1 is recommended where black medic has become established. Soil testing can confirm low phosphorus levels.
Source: Virginia Polytechnic Institute & State University