Traveling through southwest Ohio this weekend, I noticed ever-expanding patches of birdsfoot trefoil (Lotus corniculatus) along roadways, in landscapes, and in home and commercial lawns. Yet another story of dueling plant cultivation interests. This perennial, spreading, herbaceous legume is native to Europe and Asia. It was introduced into North America for use as a forage crop harvested for hay or used in pastures. Plants can survive and thrive in a wide range of soil and environmental conditions that would limit the use of other forage crops such as alfalfa. Indeed, you can still find agronomy resources on the web, mostly written in the 1990s, touting the virtues of birdsfoot trefoil as a tough forage crop.
These publications are sprinkled among web postings warning readers of the invasive nature of birdsfoot trefoil. In recent years, this tough plant has gradually moved from celebrated crop status to inglorious weed status in turfgrass, landscapes, and naturalized areas. This includes prairie establishment: burning birdsfoot trefoil actually enhances seed germination.
The bright yellow flowers are smaller than the flowers of dandelions, bigger than those of black medic and from a distance may look like buttercups. A closer inspection will reveal the flowers are sometimes tinged in red and grow in clusters of 5 - 10. They have the general appearance and structure that is shared with other members of the bean family, Fabaceae (previously Leguminosae). Heavy flowering occurs from mid-June throughout July and into August.
Birdsfoot trefoil spreads by seeding, underground rhizomes, and above ground runners. Individual plants quickly spread to form a dense mat in both lawns and landscapes. Mowed plants will continue to spread along the ground; however, the plants will rise in between mowings to tower above the surrounding turfgrass. Plants may grow to a height of 20 - 40" in surrounding landscapes. Birdsfoot trefoil has 3 leaflets at the tip of the leaf and 2 stipules near the base of the petiole making it look like it has 5 leaflets. The plant gets its name from the very distinctive arrangement of seed pods; they resemble the foot of a bird.
Infestations of this non-native opportunistic weed in turfgrass is associated with openings in weakened lawns so management begins with maintaining thick, healthy turfgrass. This includes following proper fertilization and watering programs 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; however, multiple applications may be required to exhaust regrowth from the rhizomes.