Clover

Description

Clover is the common name given to a group of approximately 300 leguminous plants in the genus Trifolium, in the family Fabaceae. Several species are cultivated specifically for fodder. The most commonly cultivated is white clover, Trifolium repens. Clover species are generally small and are usually trifoliate (leaves possess three leaflets) although some species possess five or seven leaflets. The clover plant has smooth stems and produces small red, purple, white, or yellow flowers made up up many florets. Clover species can be can be annual, biennial or short-lived perennials. White clover may live for 3–5 years, and can reach a height of 20–30 cm (8–12 inches). Clover may also be referred to as Ladino clover, Dutch clover or trefoil and it originates from Europe.


Uses

Clover is mainly cultivated to provide pasture or to protect soil. It may be harvested and used as forage, hay or silage.


Propagation


Basic requirements
White clover is the most widely grown clover in the world, growing best in a cool, moist, temperate climate. It can be grown on a wide range of soils but performs best in well-draining clay or loam as opposed to sandy soils. The plant will grow optimally at a soil pH of 5.5 and 7.0. Dry soils are not recommended due to the shallow root system. Clover tolerates shade, repeated mowing and field traffic very well making it well suited to use as a cover crop.

Planting
Clover is direct seeded either by drilling or broadcasting. When growing clover as a commercial crop, a higher yield will be obtained in warmer areas if the seed is inoculated with Rhizobacteria before planting. Inoculation is not necessary if an inoculated clover crop was grown in the same field within the past 3 years or in colder regions where nitrogen-fixing bacteria can persist in the soil. If broadcasting seed, spread 5–14 lb (2.25–6.35 kg) of seed per acre and cover. When drilling seed, 3–9 lb (1.4–4 kg) of pure seed should be planted per acre to a depth of 6–12 mm (1/4 – 1/2 in). Clover is also commonly sown into an existing grass pasture or with grass seed to establish a mixed pasture. Seeding rates into an existing grass pasture should be 2–4 lb (0.9–1.8 kg) per acre. The soil should be kept moist after seeding to promote germination.

General care and maintenance
If grown as a forage crop mixed with grass, management should be aimed at maintaining clover at 40 to 50% of the total cover. Grazing to a stubble height of 5 cm (2 in) favors the growth of the clover, whereas lighter grazing will favor the growth of grass. The pasture should be fertilized with nitrogen and phosphorous depending on the needs of the particular soil. When grown as a living mulch, clover should be mowed as required and killed off when no longer needed. Clover can be killed by rototilling, undercutting or moldboard plowing. White clover can be persistent and it is necessary to kill off the root system to effectively kill the plants.


References

Clark, Andy (ed.). 2007. Managing Cover Crops Profitably, 3rd ed. Sustainable Agriculture Network, Beltsville, MD. Available at: http://www.mccc.msu.edu/documents/man.... [Accessed 12 November 14]. Free to access.

Hall, M. H. (1993). White Clover. Agronomy Facts 22. Penn State University Cooperative Extension. Available at: http://pubs.cas.psu.edu/FreePubs/pdfs.... [Accessed 12 November 14]. Free to access.

USDA (2002). White Clover. Trifolium repens L. Plant Fact Sheet. United States Department of Agriculture. Natural Resources Conservation Service. Available at: http://plants.usda.gov/factsheet/pdf/.... [Accessed 12 November 14]. Free to access.

Smith, J. & Valenzuela, H. (2002). White Clover. College of Tropical Agriculture and Human Resources, University of Hawai'i at Monoa Cooperative Extension Service. Available at: http://www.ctahr.hawaii.edu/oc/freepu.... [Accessed 12 November 14]. Free to access.




Common Pests and Diseases

Root rot
Fusarium spp.

Symptoms
Plant stunted and yellow; some roots show tan to red coloration; infected seedlings die quickly; poor plant stand
Cause
Fungi
Comments
Disease spreads more rapidly in the presence of unfavorable growing conditions (e.g. drought or
harsh winter)
Management
Maintaining soil potassium, phosphorous and an optimum soil pH can help protect plants from disease; follow recommended harvest schedule; if disease is present in soil a rotation away from legumes for a period of at least three years is desirable

Common leaf spot
Pseudopeziza trifolii

Symptoms
Small circular brow-black spots with uneven margins on leaves; leaves turning yellow and dropping from plant
Cause
Fungus
Comments
Favors cool, wet weather; over winters on crop debris; more common during periods of high rainfall
Management
Harvest infected early to avoid severe infections; rotating crops may reduce incidence of disease

Clover rot
Sclerotinia trifoliorum

Symptoms
Small brown to black lesions on leaves which coalesce and cause the leaves to dry out and drop, fungus may also affect stems, causing the plant to wither and die; dead plant material on the ground may be covered in white mold
Cause
Fungus
Comments
Fungus can survive in soil for up to 5 years; severely infected pastures can be reduced to masses of rotting plants on the ground
Management
Allowing close grazing or cutting of the stand reduces humidity around plants which in turn will slow the progression of the disease; plow plant material deeply into soil; rotation to a non-susceptible host for a period of 4-5 years is recommended id disease is present

Alfalfa weevil
Hypera postica

Symptoms
Leaves skeletonized and appear bronzed; plants may be completely defoliated; adult insect is a dark gray beetle 0.5 cm (0.2 in) in length; larvae are pale green grubs with a thin white line down the center of their back and a brown head; larvae spin a cocoon and pupate on leaves or in soil
Cause
Insect
Comments
Weevils overwinter in crop debris and emerges in Spring; both adult insects and larvae damage plants
Management
Treatment of alfalfa weevils should be focused on the period before the first cutting; cutting the crop before budding is organically acceptable and can prevent serious damage and kill off most weevils; other control methods include the application of appropriate insecticide

Aphanomyces root rot
Aphanomyces spp.

Symptoms
Infected seedlings have yellow cotyledons (seed leaves) with other leaflets beginning to turn yellow; seedlings dying back, seedlings with stunted growth; decaying roots in established plants leading to symptoms resembling nitrogen deficiency
Cause
Oomycete
Comments
Disease is more easily spread in moist soils and over a wide range of temperatures
Management
Maintaining soil potassium, phosphorous and an optimum soil pH can help protect plants from disease; follow recommended harvest schedule; if disease is present in soil a rotation away from legumes for a period of at least three years is desirable

Alfalfa mosaic
Alfalfa mosaic virus (AMV)

Symptoms
Yellow streaks parallel to leaf veins; yellow-green mottling of leaves; distorted leaves; stunted plant growth
Cause
Virus
Comments
Virus overwinters on many perennial plants; transmitted by aphids; also spread via infected seed and pollen
Management
Plant resistant varieties; control aphid populations on plants; use virus free seed

Red clover mosaic
Red clover vein mosaic virus (RCVMV)

Symptoms
Yellow leaf veins and/or yellow tissue adjacent to leaf veins
Cause
Virus
Comments
Transmitted by aphids; symptoms evident in cool weather on young leaves; renders clover plant more susceptible to secondary infections with other diseases and drought.
Management
Plant resistant cultivars; control aphid populations on plants; use virus free seed