HPIPM:Yellow sweet clover

Taxonomy

Domain	Eukarya
Kingdom	Plantae
Phylum	Magnoliophyta
Class	Magnoliopsida
Superorder	Rosanae
Order	Fabales
Family	Fabaceae
Genus	Melilotus

Scientific Name

Melilotus officinalis

Common Name

yellow sweet-clover

Yellow sweet clover (Melilotus officinalis (L.) Lam.)

Compiled by Melissa Graves, and Evette Allison, Montana State University, compiled by the following sources:

http://www.illinoiswildflowers.info/weeds/plants/yl_swclover.htm

http://www.invasive.org/weedus/subject.html?sub=6008

http://www.dnr.state.mn.us/invasives/terrestrialplants/herbaceous/whitesweetclover.html

http://www.invasive.org/weedcd/pdfs/wow/yellow_sweetclover.pdf

http://plants.usda.gov/java/profile?symbol=meof

http://www.agdepartment.com/noxiousweeds/pdf/Yellowsweetclover.pdf

Identification and Life Cycle

Yellow sweetclover is an annual to biennial species, but has occasionally been reported as a short-lived perennial. This Eurasian native was introduced to North America in the 1600s as a forage crop. It can range from two to seven feet in height. Larger plants branch frequently and are somewhat bushy in appearance. Shorter plants are less branched and appear lanky. The stems are more or less erect, but may sprawl across the ground. They tend to be glabrous, furrowed, and angular, sometimes with light red ribbing on the lower stems. The alternate leaves are trifoliate-compound and hairless. Each leaflet is about ¾" long and ¼"wide. They are typically oblong, oblanceolate, or obovate in shape, and dentate along the middle or upper margin. Terminal leaflets have a short petiolule (stalk at its base). Lateral leaflets are nearly sessile. The petiole of each compound leaf is about ½" long. Each leaf has a pair of small narrow stipules at the base of the petiole.

Small yellow flowers are produced abundantly in both axillary and terminal racemes. Each raceme is up to 6" long and has dozens of flowers. These flowers are loosely arranged along the raceme and tend to droop downward. They normally occur along one or two sides of the raceme, but may also occur in whorls. The slender corolla has 5 yellow petals, standard, keel, and two side petals. The tips of the flowers tend to curve upwards. The base of the corolla is surrounded by a light green tubular calyx, with 5 pointed teeth.

Habitats

Plants can be found along agricultural land, roadsides, in open fields, pastures, railway embankments, river banks, and waste or disturbed areas. This species is drought tolerant, grows well in direct sunlight, and is fairly winter hardy. It does not do well in areas of prolonged flooding. These plants are most commonly found on calcareous soils. It grows best on rich loams and clay loams to sandy loams, with pH levels of 6.5 or higher. It will also grow on highly alkaline soils.

Impacts

Sweetclover can impact a wide variety of habitats. In cropping systems, it decreases crop yield through competition for sunlight, soil water, and nutrients. This species is a threat to prairies because it spreads rapidly into open areas and may out-compete the native species for available resources. It causes similar issues in rocky, open, calcareous glades and woodlands, where it can reduce natural communities by overtopping and shading native sun-loving species. Sweetclover disease or ‘bleeding disease’ is a condition that can appear in cattle after feeding on spoiled sweetclover or silage. The plant tissue is high in coumarin which inhibits coagulation of blood, often causing bloat in cattle.

Biology and Ecology

Yellow sweetclover spreads by reseeding and may form large colonies at favorable sites. Blooming occurs from late spring to early fall, peaking in early to mid-summer and lasts for about 2 months. Each flower produces a small, ovoid seedpod with a flattened beak . Seedpods typically contain 1-2 seeds. The seeds are tannish yellow, somewhat flattened and kidney-shaped. Seed maturation begins in July and continues through autumn, with some seeds remaining on the plant over the winter. Each yellow sweetclover plant is capable of producing more than 100,000 seeds, which may be viable in the soil for more than 20 years.

Biological Control

A few biological control agents have an impact on these plants. The sweetcloverweevil, Sitona cylindricollis, is capable of causing severe damage to this plant. Adultinsects feed on the foliage and larvae feed on the roots of the plant. The sweetclover root borer, Walshia iscecolrella, is a native insect that may damage the plants on rare occasions. An ash-gray blister beetle, Epicauta fabricii, a striped blister beetle, Epicauta vittata, and a margined blister beetle, Epicauta pestifera, are also known to feed on sweetclover.

Mechanical and Cultural Control

Hand pulling first year stems of yellow sweetclover may be more effective conducted in late summer or early fall when the plants are still green and easily detected among the dried grasses.

For very dense small patches, cutting with a power brush-cutter using a heavy duty saw blade has been effective. The stand should be cut just before flowering, and checked a week later for missed or partly cut plants. It is critical to catch the plants before seed onset and cut any missed stems soon after.

Prescribed burning has had variable results. Dormant season burns conducted in late fall or early spring, followed by a later spring burn the following growing season, may be the most effective burn schedule in reducing populations. If a follow-up burn is conducted prior to seed set, new seed production can be prevented.

In the table below are examples of herbicides that can be used to manage yellow sweet clover.

Consult and follow all herbicide labels for additional rate, application, crop restrictions, and safety information. Additional herbicide information can be found at http://www.greenbook.net.

Due to constantly changing labels, laws and regulations, the sponsors of this web site assume no liability for the suggested use of any chemicals noted in the management section. Contact your local pest management personnel for current information on labeled pesticides that can be used for the intended plant disease, insect pest or weed.

References

For more information and images please visit IPM Images: http://www.ipmimages.org/search/action.cfm?q=sweet%20clover&Start=1&results=67