Melilotus officinalis (L.) Lam
Melilotus officinalis (L.) LamYellow Sweet Clover
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Description
Height
Yellow Sweet Clover’s height can vary from 2 to 7 feet (.6-2.3 m).Stem
Herbaceous stems are erect, furrowed, and glabrous. Tall plants are often highly branched, appearing bushy; shorter lanky plants can sprawl.Leaves
The alternate leaves are trifoliate, sparsely distributed along the stems, and have petioles up to 1 inch long with a pair of small linear stipules at the base. The grayish green leaflets are 0.5-1 inch (1-2.5 cm) long and 0.3-0.5 inch (1 cm) across. They are hairless, toothed, and oblong or oblong-ovate. The terminal leaflet has a short stalk, and the lateral leaflets are nearly sessile.Flowers
Small, yellow, mildly fragrant, pealike, short-stalked flowers form slender racemes cluster at stem tips and in leaf axils. The flower heads are 1-5 inches (3–12 cm) long. Individual flowers are 0.25-0.35 inch (7-10 mm) in length. Flowering takes place from April through September.Fruit
Fruit consist of somewhat oval-shaped pods, about 1/8 to 1/5 inch (3–5 mm) long, with a sharply ridged or veined surface that is light brown and hairless. Pods hang from downward bent stalks. Seeds are somewhat oval, smooth, dull yellowish green to orange-tan, and sometimes have purplish or brown spots.Images
Photo: Dave Powell, USDA Forest Service, Bugwood.orgMore images of Melilotus officinalis
Life History
Yellow Sweet Clover, a biennial (sometimes annual or short-lived perennial), is a member of the Fabaceae (Bean) family. Flowering spring to fall, it reproduces solely by seed. Sweet Clover leaves and flower buds contain a low level toxicant called coumarin. If Sweet Clover hay or silage is poorly cured, it can develop mold that converts the coumarin to a more toxic compound harmful to livestock. Sweet Clover nectar attracts many insects, including bees (a favorite of honeybees), wasps, flies, beetles, and butterflies. Lepidopteran larvae feed on foliage, flowers, and buds.This species is very similar in appearance to Melilotus alba, or White Sweet Clover. Some authorities regard them as the same species with differently colored flowers, classifying White Sweet Clover as a variety of Melilotus officinalis. The yellow-flowered species has a tendency to bloom about 2-4 weeks earlier, and its foliage is more green, rather than grayish green. The seedpods of Yellow Sweet Clover have transverse wrinkles, which are rarely present in the seedpods of White Sweet Clover.
Habitat
Yellow Sweet Clover occurs in open fields, roadsides, agronomic crops, and other disturbed sites. Long tap roots allow drought and winter hardiness, but it is not tolerant of prolonged flooding. Best growth is found on calcareous and near neutral soils.Origin and Distribution
Yellow Sweet Clover was introduced into North America as a forage and green manure crop in the 1900s. It occurs along roadsides, open fields, vacant lots, pastures and other disturbed, waste areas.Other States Where Invasive: AK, AL, AR, AZ, CA, CO, CT, DC, DE, FL, GA, HI, IA, ID, IL, IN, KS, KY, LA, MA, MD, ME, MI, MN, MO, MS, MT, NC, ND, NE, NH, NJ, NM, NV, NY, OH, OK, OR, PA, RI, SC, SD, TN, TX, UT, VA, VT, WA, WI, WV, WY
Federal or State Listed as Noxious Weed, Prohibited, Invasive, or Banned: AK, CO, MN, TX, WI
Sources
Cole, M. 1990. Vegetation Management Guideline: White and Yellow Sweet Clover. Illinois Department of Conservation.Haragan, P.D. 1991. Weeds of Kentucky and Adjacent States: A Field Guide. The University Press of Kentucky. Lexington, Kentucky.
Southeast Exotic Pest Plant Council. 1996. Invasive exotic pest plants in Tennessee (October 1999). Research Committee of the Tennessee Exotic Pest Plant Council. Tennessee.
Southern Weed Science Society. 1998. Weeds of the United States and Canada. CD-ROM. Southern Weed Science Society. Champaign, Illinois.
Management Recommendations
Mowing: Manual methods of control for Sweet Clover include hand pulling before seeds are set, cutting to ground level when plants are in full bloom, mowing close to the ground when seedlings are 6-8 inches (15-20 cm) tall. For very dense small patches, cutting with a power brush-cutter using a heavy duty saw blade is effective. The stand should be cut just before flowering, and checked a week later for missed or partly cut plants.Prescribed Burn: Sweet Clover response to carefully timed seasonal burns using good management practices. A burn schedule such as a dormant season burn (late fall or early spring) to stimulate germination in the subsequent growing season, followed by a later spring burn the next season to eliminate the second year plants before they set seed has been effective (Cole,1990).
Chemical: Herbicides (2,4-D) can be used to spot spray Sweet Clover. Herbicides are usually used for extremely disturbed sites (Cole,1990).