Melilotus alba Medikus

White Sweet Clover

Category
Forb/Herb

Description

Stem

Herbaceous stems are erect, branching, typically single from base, glabrous or with a few sparse hairs and furrowed.

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. Foliage is mildly fragrant with a hay scent.

Flowers

Small, white, 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 late spring to fall.

Fruit

Each flower is replaced an ovoid seedpod about 0.3 inch (10 mm) long that terminates in a beak and contains 1 or 2 seeds. The surface of each seedpod is smooth or slightly reticulated.

Images

Photo: Jamie Nielsen, University of Alaska Fairbanks, Cooperative Extension Service, Bugwood.org
More images of Melilotus alba

Life History

White Sweet Clover, a biennial (sometimes annual or short-lived perennial), is a member of the Fabaceae (Bean) family. It is a soil nitrogen fixer. 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.

White Sweet Clover is very similar in appearance to Melilotus officinalis, Yellow 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 white-flowered species has a tendency to bloom about 2-4 weeks later, and its foliage is more grayish green, rather than plain green. The seedpods of White Sweet Clover lack distinct transverse wrinkles, which are usually present on the seedpods of Yellow Sweet Clover.

Habitat

Best growth for Sweet Clovers is found on calcareous and near neutral soils. Habitats include limestone glades, thinly wooded bluffs, prairies, weedy meadows, old fields, vacant lots, areas along railroads and roadsides, and waste areas. It can invade prairies and other natural habitats, where it is regarded as a nuisance by ecologists, however, it is more common in areas with a history of disturbance. A long tap root allows drought and winter hardiness. White Sweet Clover demonstrates more tolerance for periodic flooding than Yellow Sweet Clover.

Origin and Distribution

White Sweet Clover, native to central Europe and the Mediterranean region, was introduced as a green manure for fields and as forage for livestock. It thrives in disturbed and 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.

Southern Weed Science Society. 1998. Weeds of the United States and Canada. CD-ROM. Southern Weed Science Society. Champaign, Illinois.

DiTomaso, J.M., M.L. Brooks. E.B. Allen. R. Minnich, P.M. Rice, G.B. Kyser. Control of Invasive Weeds with Prescribed Burning. Weed Technology. 20: 535-548.

Uchytil, Ronald J. 1992. Melilotus alba. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory.
http://www.fs.fed.us/database/feis/plants/forb/melalb/all.html

Management Recommendations

Mechanical: Hand-pulling Sweet Clover is best done in the fall. In the spring the root crown must be removed when the ground is moist and before it begins to flower. Hand cutting stems just before flowering or on lower stems that dieback before flowering, usually does not resprout. Be sure to cut close to the ground (Cole, 1990).

Prescribed Burn: Prescribed burning is also used to contol Sweet Clover (Uchytil, 1992). They must be burned in April of the first year, which causes the seeds to germinate (Cole, 2006; DiTomaso et al, 2006). After the first burn seed germination is high (Uchytil, 1992) and there is a high density of M. alba. In May of the second year when the plants are 3.28-6.56 ft (1-2 m) high they should be burned again, which kills emerging shoots before they seed. This procedure should be followed by two years of no burn (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).