Black Medic

Biology: Black Medic (Medicago lupulina) is a summer annual (or less commonly a winter annual) broadleaf weed that can be found throughout the United States. Seeds germinate in the spring and are capable of establishing in drought-prone or disturbed soils. is a legume, meaning that it has the capabilities to fix its own nitrogen; thus, allowing it to out compete turf in nutrient-poor soils as well. These factors, in combination with its ability to tolerate low mowing heights, make black medic a common weed in lawns and other high-maintenance turf throughout Indiana.

Identification: has low-growing, prostrate, somewhat square stems that extend underneath the turf canopy to lengths up to 2 feet long. Despite the production of these invasive stems, it germinates from seed in early autumn or spring. Black medic stems do not have the ability to root as they establish; however, the plant is well-anchored by a deep, central taproot. The leaves are trifoliate (3 leaves), dull green on the top, pale green below, wedge-shaped, as long as they are broad, toothed near the tip, and display a projecting tip or spur at the apex. Black medic can often be mistaken for oxalis (yellow and creeping woodsorrel) and white clover which also have very similar trifoliate leaf arrangements. However, the leaf stem (petiole) of the center leaf is slightly longer than the two lateral leaves, thus distinguishing it from oxalis and white clover. It produces a very tight, compressed cluster of small yellow flowers in the spring and until the fall. Once the flowers mature, they form a very tightly coiled black seedpod, hence the name ‘black medic’.

Cultural Control

To manage it effectively, use cultural practices. This weed struggles in shade, so a thick turfgrass canopy can suppress it. Since ot fixes nitrogen, proper fertilization controls the weed and boosts turf health. Dry soil often invites this weed, so consider increasing irrigation. For small infestations, pull the weeds early, focusing on removing the taproot.

Biological Control Methods

No specific biological controls target Black Medic yet. Use organic postemergence herbicides like pelargonic acid (Scythe), acetic acid, or Eugenol for control. These non-selective herbicides are best for spot treatments. Products with iron HEDTA may help, but research is ongoing.

Chemical Control Strategies

For Black Medic, postemergence treatments work better than preemergence ones. Mixtures of 2,4-D, dicamba, MCPP, or MCPA are effective. Selective control options like Turflon Ester or Drive might need multiple applications.