The extent of the invasion of Birdsfoot Trefoil (Lotus corniculatus, family Fabaceae) in Ohio is now being revealed through a canary yellow floral display. The yellow flowers are smaller than dandelion flowers, bigger than those of black medic, and resemble buttercups from a distance.
Birdsfoot trefoil is a perennial herbaceous legume that is native to Europe and Asia. It was imported with good intentions but is now gaining weed status in lawns, landscapes, and naturalized areas in Ohio.
Birdsfoot trefoil was introduced into North America for use in pastures or as a forage crop harvested for hay. The tough plants can survive and thrive where other forage plants, such as alfalfa, wither away. Indeed, for years, birdsfoot trefoil was hailed as the answer to producing high-quality forage for cattle and sheep on marginal lands.
However, over time, birdsfoot trefoil has gradually transformed from a celebrated Dr. Jekyll to an inglorious Mr. Hyde. It’s proven itself to be a stubborn weed in turfgrass, landscapes, and naturalized areas. Plants are spread by seeding, underground rhizomes, and above-ground runners. It’s a relentless spreader where plant competition is wimpy or nonexistent.
Once established, individual plants quickly form a dense mat. In lawns, mowed plants creep along the ground but bolt between mowings to tower above the surrounding turfgrass. In landscapes, plants may rise to a height of 20 - 40" to over-shadow annuals and even some herbaceous perennials.
The dark green foliage has 3 leaflets at the tip of the leaves and 2 stipules near the base of the petiole making it look like it has 5 leaflets. The bright yellow flowers are sometimes tinged in red and grow in clusters of 5 – 10.
The flowers and seed pods look like those produced by peas or beans which is no coincidence since they’re all in the same family. Heavy flowering, and thus seeding, occurs from June throughout July and into August. The plant gets its common name from the very distinctive appearance of the developing seed pods; they resemble the foot of a bird.
Infestations of this non-native opportunistic weed in turfgrass are associated with openings in weakened lawns so management begins with maintaining thick, healthy turfgrass. This includes proper fertilization and watering as well as cutting turfgrass high to support the development of healthy root systems.
Fortunately, birdsfoot trefoil is susceptible to most post-emergent broadleaf herbicide products labeled for use on turfgrass. Of course, the key is to start applications before plants begin to produce seeds and multiple applications may be required to exhaust regrowth from the rhizomes. Management in landscapes may require a combination of pre- and post-emergent herbicides as well as the judicious use of mulch to smother the seeds.