Black medic flower. The Australian weed Identification chart avoids the confusion that can occur between this weed, oxalis and white clover

Black Medic (Medicago lupulina)


Black Medic is a summer annual that is a common prostrate weed and forms a dense, mat-like cover across the turf. It is often called Yellow Trefoil, and is a summer annual that germinates in the late spring. It then continues to grow through the heat of the summer. Once conditions cool down, it dies off.

After you finish reading this, you will be able to:

  • Identify Black Medic or Yellow Trefoil.
  • Know what conditions favour Yellow Trefoil.
  • Know the best cultural and chemical options to control Black medic or Yellow Trefoil.


Although not directly toxic to livestock, if they eat enough of it, Black Medic causes serious gastric issues.

More information on common lawn weeds is in our weed ID chart. What they reveal about soil conditions is in our blog on indicator weeds.


How to Identify Black Medic.

Black Medic is a low-growing weed and has three heart shaped trifoliate leaves. These leaves have shallow teeth towards their tips and dark spots near the centre.

Category: Broadleaf (Dicot).

Flower: Yellow Trefoil has single round yellow flowers or flowers in clusters of up to four.

Height: It grows up to 10 to 60 cm in height.
Leaf length: The leaves of medic are 12 to 18 mm long.
Leaf width: Leaf width is 3-10 mm wide.

Reproduction: Black Medic reproduces by seed.
Comments: Coarse hairs cover the leaves.

Habitat: This weed is a good indicator of soil problems. It thrives in drought, low nitrogen, well-drained, compact soils and bare areas. Yellow Trefoil indicates that you are mowing too low, and your turf struggles to compete.




How to remove Black Medic from your lawn.

Both cultural and chemical methods remove Yellow Trefoil from lawns and turfgrass.

Cultural control.

Hand pull or use a weeding tool. As it favours compact soils, soil aeration can also help manage this. Also, bare in mind that keeping N up to your turfgrass helps deter this weed.

Chemical control.


There are several turf herbicides that control Black Medic, but treatment is best in the late spring to early summer and early to late autumn. The best time to apply post-emergent herbicides is as early in the season as you can as this is when plants are small. You may need several applications to get the best results.

The herbicide Dithiopyr provides some pre-emergent control in lawns but is not registered in Australia for this.

Non selective options include Glyphosate (Rapid Fire 800). If you use this and water quality is an issue then we recommend the use of ProForce Manta Ray.