Alfalfa

Description

Alfalfa, Medicago sativa, is an herbaceous perennial in the plant family Fabaceae (peas and beans) which is primarily grown as a forage crop which can be grazed by animals or harvested as hay to be used as an animal feed. Alfalfa has a deeply penetrating taproot and the stems of the plant branch from a woody base, growing upright and erect or along the ground. The leaves of the plant are made up of three individual leaflets (trifoliate) which are are narrow and oval or oblong in shape with a smooth upper surface and slightly hairy lower surface. Alfalfa plants produce flowers on racemes (flower stalks) and each raceme possesses 10–35 densely packed purple flowers. Alfalfa produces spirally coiled seed pods each containing 2–6 seeds. Pods may have a smooth or hairy outer surface. Alfalfa plants can reach a height of 120 cm (47 in) and live for between 3 and 8 years. Alfalfa is also commonly referred to as lucerne and is believed to have originated in Caucasus area, north-western Iran and north-eastern Turkey.

Crop Details

Scientific Name: Medicago sativa 

Common Name: lucerne, purple medic (En); alfalfa, mielga (Sp); luzerne (Fr); luzerna (Pt); अल्फाल्फा (Hi).




Uses & Benefits

Alfalfa leaves are edible and can be eaten as a leafy vegetable. Alfalfa is used primarily as forage for animals and is cut and stored as hay or silage. As a legume, the plant fixes nitrogen so can be used to increase nitrogen in the soil and is a commonly used cover crop. Alfafa is a good source of vitamins, calcium, iron, phosphorus and potassium.

Besides its use as feed, alfalfa has been traditionally used as a medicinal herb for humans. Its seeds and dried leaves can be consumed as supplements, or sprouted as edible alfalfa sprouts. 




Varieties of Alfalfa

Farmers growing alfalfa should consider the following factors when selecting varieties to plant:

Purpose: Decide why you're growing alfalfa. If it's for making hay, focus on varieties that can withstand time and yield a lot. If it's for grazing, pick types that can grow back quickly after grazing. 

Dormancy & Winterhardiness: Check the dormancy rating of the variety you want to plant. Ratings range from 1 (very dormant) to 10 (not dormant). In places with warm winters and little frost, go for varieties with ratings of 9 or 10.

Disease and Pest Resistance: Choose varieties that can at least moderately resist common diseases like bacterial wilt, fusarium wilt, phytophthora root rot, verticillium wilt, and anthracnose.

Forage Yield: It's a good idea to see if a variety has performed well in your specific region before deciding to plant it. This helps ensure a good yield.




Propagation

Basic Requirements

Alfalfa is adapted to grow in a wide variety of environments but it requires careful management. Alfalfa grows best in deep, fertile, well-draining soils with a pH between 6.0 and 7.0. Alfalfa has a long taproot and quickly depletes nutrients from the soil. If grown in a soil that is poor in nutrients, the crop may require the addition of copious amounts of fertilizer. The vigorous root system means that alfalfa can tolerate dry periods and still give a good yield.

Seeding

Soil should be well prepared before planting alfalfa seeds. A firm seedbed is recommended to improve the stand by improving seed contact with the soil. This helps seeds retain moisture and prevents new roots from drying out. The soil can be firmed before planting by using a roller. The seedbed should also be free of weeds and kept moist. 

Alfalfa crop has tiny seeds and it's crucial to plant them at the right depth.The optimal planting depth varies depending on the type of soil. On medium and heavy soil, plant the seed 1/4 inch (0.6 cm) to 1/2 inch (1.3 cm) deep, while on sandy soil, plant it 1/2 to 1 inch deep. If there's enough moisture, you can plant the seed shallower, but if the soil is dry, you should plant it deeper. While sowing, cover the seeds with soil that is moist enough to promote germination, but not so much that the shoots can't break through the surface. 

General Care and Maintenance

The alfalfa stand should be kept free from weeds. The easiest way to achieve this when the crop is being grown on a commercial scale is with the use of a pre-plant herbicide. There are several of these product available for use on alfalfa. Fertilizer should be applied in accordance with soil test results. Lime, phosphorus and potash are the most important nutrients for a healthy alfalfa stand.

Harvest

Alfalfa is harvested at different times depending on it's intended use. Alfalfa which is cut between thee late bud and early bloom stage generally gives acceptable yields of high quality feed without reducing the quality of the stand. In contrast, repeated harvest of alfalfa which is till in the vegetative stage of growth leads to a reduced stand. In the first year, alfalfa can generally be harvested twice without any detrimental effect on winter survival; once in summer prior to the flowers emerging, and once later in the year with the date depending on location. Alfalfa is usually harvested by combine and baled as hay or cut for direct feeding to animals.




References

CABI Crop Protection Compendium. 2014. Medicago sativa datasheet. [Accessed 05 November 14]. Paid subscription required

Frate, C.A. & Davis, R.M. (2007) Alfalfa diseases and management In C.G. Summers and D. H. Putnam (eds)., Irrigated alfalfa management for Mediterranean and desert zones. Chapter 10. Oakland: University of California Agriculture and Natural Resources Publication 8296. Available at: http://alfalfa.ucdavis.edu/IrrigatedAlfalfa/pdfs/UCAlfalfa8296Disease_free.pdf. [Accessed 05 November 14]. Free to access

Lacefield, G., Henning, J.C., Rasnake, M. & Collins, M. (1997) University of Kentucky College of Agriculture Cooperative Extension Service Publication. Alfalfa: the Queen of Forage Crops. Available at: http://www2.ca.uky.edu/agc/pubs/agr/agr76/agr76.pdf. [Accessed 05 November 14]. Free to access

Undersander, D., Gray, F., Kelling, K. & Rice, M. National Alfalfa and Forage Alliance Publication. Alfalfa Analyst. Available at: http://www.alfalfa.org/pdf/AlfalfaAnalyst.pdf. [Accessed 05 November 14]. Free to access

Undersander, D., Cosgrove, D., Cullen, E., et al. (2011). Alfalfa Management Guide. American Society of Agronomy, Inc., Crop Science Society of America, Inc., and Soil Science Society of America, Inc. Retrieved from https://www.agronomy.org/files/publications/alfalfa-management-guide.pdf [Accessed 13 March 2024]. Free to access




Common Pests and Diseases

Diseases

Category : Viral

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
Transmitted by aphids; also spread via infected seed and pollen.
Management
Plant resistant cultivars; control aphid populations on plants; use virus free seed.

Category : Fungal

Anthracnose Colletotrichum trifolii

Symptoms
Large diamond shaped lesions with white centers on lower portion of stems; young dead shoots take on a characteristic "shepherds crook" appearance.
Cause
Fungus
Comments
More common in warm weather and periods of high moisture.
Management
Cannot be managed in established alfalfa stands; cut crop before major losses occur.

Common leaf spot Pseudopeziza medicaginis

Symptoms
Small circular brow-black spots with uneven margins on leaves; leaves turning yellow and dropping from plant; raised brown fungal fruiting bodies may be visible in cool wet weather
Cause
Fungus
Comments
More common during periods of high rainfall
Management
Harvest infected alfalfa early to avoid severe infections which reduce hay quality; rotating crops may reduce incidence of disease

Downy mildew Peronospora trifoliorum

Symptoms
Young leaflets may be dwarfed, twisted and cupped downward; light green or yellow blotches on leaves; a gray downy growth may be visible on infected leaves during cool, wet weather or during periods of high humidity.
Cause
Fungus
Comments
Pathogen spread by wind or by splashing water.
Management
Grow resistant cultivars; cut alfalfa crop while still in prebloom stage; sow crop in Spring to reduce chance of seedlings becoming infected.

Fusarium wilt Fusarium oxysporum f. sp. medicaginis

Symptoms
Wilting shoots followed by bleaching of leaves and stem; rapid wilting of stems on only one side of plant; may be a reddish tinge to leaves; red streaks in root stele.
Cause
Fungus
Comments
Disease emergence favored by high soil temperatures.
Management
No satisfactory method of management; plant resistant alfalfa varieties.

Lepto leaf spot Leptosphaerulina trifolii

Symptoms
Small red-brown flecks on leaves and petioles which develop into lesions with tan center and irregular brown margins; leaves become necrotic but remain attached to the plant.
Cause
Fungus
Comments
Occurs wherever alfalfa is grown.
Management
Disease incidence and severity can be reduced by planting cultivars reported to have some resistance, using certified seed and rotating crop with a resistant plant such as soybean for at least 2 years.

Category : Oomycete

Aphanomyces root rot Aphanomyces euteiches

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
Grow varieties that have some resistance to the disease; only plant alfalfa in well draining soil.

Phytophthora root and stem rot Phytophthora megasperma

Symptoms
Chlorotic or reddish leaves which drop from plant; rotted roots which are yellow-brown in color; roots eventually turn black.
Cause
Fungus
Comments
Disease more prevalent in water saturated soil.
Management
Grow resistant cultivars; try to improve drainage if soil has tendency to be waterlogged.

Category : Bacterial

Bacterial wilt Clavibacter michiganense subsp insidiosus

Symptoms
Dead plants scattered around field; stunted plants with small leaves and stems; bunchy appearance of plants; leaves curling upwards; plants wilting during day and recover at night; chlorotic leaflets; death of plants.
Cause
Bacterium
Comments
Occurs wherever alfalfa is grown, important disease in the US.
Management
Plant resistant cultivars.

Category : Fungal, Oomycete

Damping off Pythium ultimum
Pythium irregulare
Pythium violae
Rhizoctonia solani
Phytophthora megasperma

Symptoms
Failure of seedling to emerge; light brown, seedlings with light brown water-soaked roots and stems; collapse of plants; plant dry up and die.
Cause
Oomycete Fungi
Comments
Occurs more often in cold temperatures when growth of seedlings is slow and in moist soil.
Management
Treat seeds with fungicide prior to planting.

Pests

Category : Insects

Alfalfa caterpillar Colias eurytheme

Symptoms
Defoliation of plants; entire leaf consumed, including midrib; adult insects are yellow-orange to white butterflies; larvae are bright green, velvety caterpillars which can reach 3.8 cm (1.5 in) in length; larvae have a white strip running down the side of their body.
Cause
Insect
Comments
Damage is most severe when eggs are laid in recently cut fields.
Management
Avoid unnecessary applications of insecticides to promote populations of natural enemies; organically grown alfalfa can be treated with Bacillus thuringiensis; harvest crop early to avoid serious damage.

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.

Aphids (Cowpea aphid, Blue alfalfa aphid, Pea aphid, etc) Aphis craccivora
Acyrthosiphon kondoi
Acyrthosiphon pisum

Symptoms
Small soft bodied insects on underside of leaves and/or stems; aphids are generally green in color but cowpea aphid is black and colonizes stems; aphids inject a powerful toxin into alfalfa which stunts plant growth and may kill the plant; aphids also secrete a sticky, sugary substance called honeydew which encourages the growth of sooty mold on the plants.
Cause
Insect
Comments
Blue alfalfa aphid and pea aphids prefer cooler temperatures and are most abundant in Spring and Fall; cowpea aphids are generally a sporadic pest but are most common in Spring.
Management
Insecticides are generally only required to treat aphids if the infestation is very high - plants generally tolerate low and medium level infestation; insecticidal soaps or oils such as neem or canola oil are usually the best method of control; always check the labels of the products for specific usage guidelines prior to use.

Beet armyworm Spodoptera exigua

Symptoms
Singular, or closely grouped circular to irregularly shaped holes in foliage; heavy feeding by young larvae leads to skeletonized leaves; shallow, dry wounds on fruit; egg clusters of 50-150 eggs may be present on the leaves; egg clusters are covered in a whitish scale which gives the cluster a cottony or fuzzy appearance; young larvae are pale green to yellow in color while older larvae are generally darker green with a dark and light line running along the side of their body and a pink or yellow underside.
Cause
Insect
Comments
Insect can go through 3–5 generations a year.
Management
Organic methods of controlling the beet armyworm include biological control by natural enemies which parasitize the larvae and the application of Bacillus thuringiensis; there are chemicals available for commercial control but many that are available for the home garden do not provide adequate control of the larvae.

Threecornered alfalfa hopper Spissistilus festinus

Symptoms
Stems girdled causing part of plant to above to break and turn red, purple or yellow; adult insect is green and wedge-shaped, tapering towards rear end; insect has a triangular area on back visible from above and piercing-sucking mouthparts; nymphs are soft bodied and gray-white in color.
Cause
Insect
Comments
Insect also a pest of other plants including soybean; may be 3-4 generations of insect per year.
Management
Applications of appropriate insecticide if insect becomes problematic.
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