Sorghum

Description

Sorghum, Sorghum bicolor, is an annual or perennial grass in the family Poaceae grown primarily for its grain. Sorghum has an erect solid stem with one or more tillers (additional shoot that grows subsequent to the parent shoot) and curving leaves which are arranged alternately on the stems and are lance-like in shape, measuring 30–135 cm (12–53 in) in length. The inflorescence of the plant consists of racemes of spikelets arranged on branches at the head of the plant. The spikelets are paired and have 2 florets. When the plant flowers, yellow anthers begin to appear on the head. Sorghum is usually grown as an annual, harvested after one growing season and can grow to a height of 4 m (13 ft). Sorghum may also be referred to as broomcorn and may have been cultivated from wild ancestors in Ethiopia.


Uses

Sorghum is a staple food source in Africa and Asia where the grain can be boiled and eaten in a manner similar to rice, roasted or popped. Sorghum grain can also be used to produce flour which can be used to make bread. Sorghum grain is also used extensively as animal feed and as fodder. Sweet sorghum varieties can be processed into syrups and molasses.


Propagation


Basic requirements
Sorghum is a warm-season grass which is adapted to grow in a wide range of soil types and climatic conditions, tolerating waterlogging and poor soils. Sorghum will perform optimally when planted in deep, fertile and well draining loam soils with a pH between 6.0 and 7.5. Sorghum is best grown in hot tropical or semi tropical environments but it will tolerate a range of temperatures. The crop tolerates hot, dry conditions better than corn or soybeans but it will be killed by frost. Soil temperatures of at least 18.3°C (65°F) are required for germination.

Propagation
Sorghum is propagated directly from seed. Seed should only be sown in soils which have warmed to at least 18.3°C (65°F). Ideally, seeds should be sown in a finely prepared seed bed but seeds are often sown in furrows following plowing or broadcast. A wide range of row spacings are used successfully in sorghum cultivation with the final spacings being dependent of climatic conditions and available moisture. Under favorable conditions for sorghum growth, plants should be spaced 12–20 cm (4.7–7.9 in) apart, allowing 45–60 cm (17.7–23.6 in) between rows. This spacing produced an optimal planting density of approximately 120,000 plants per hectare.

General care and maintenance
in tropical and subtropical regions, sorghum is predominantly grown as a rainfed crop which is planted after the onset of monsoon season. In temperate areas, where annual rainfall is not sufficient to meet the growing requirements of the crop (at least 400-600 mm per year), supplemental irrigation may be required. in subsistence farming, fertilizers are rarely applied to the crop. However, in countries such as the United States, where sorghum is cultivated on a large scale, high doses of nitrogen fertilizer are applied, often up to 150 lbs of nitrogen per acre, although rates are adjusted to suit existing levels of nitrogen in the soil, soil moisture and expected yields. Sorghum fields should be kept free from weeds which compete with the crop and reduce yields. Weeds are often removed from between rows by hand in smaller fields, or by tilling in large scale production. Herbicides are often not effective at removing weeds during the growing season and are applied prior to planting.

Harvesting
Sorghum can be harvested by hand or by combine. When harvesting by hand, the heads or whole plants may be cut. Sorghum should be harvested when the grain moisture content is between 18 and 23% and may be ready for harvest when the leaves are still green. After harvest, grains are removed from the heads by threshing.


References

CABI Crop Protection Compendium. (2010). Sorghum bicolor (sorghum) datasheet. Available at: http://www.cabi.org/cpc/datasheet/50633. [Accessed 09 April 15]. Paid subscription required.

Espinoza, L. & Kelley, J. (Eds.) Grain sorghum production handbook. Available at: http://www.uaex.edu/publications/pdf/.... [Accessed 09 April 15]. Free to access.

Frederikson, R. A. & Odvody, G. N. (Eds.) (2000). Compendium of sorghum diseases. American Phytopathological Society Press. Available at: http://www.apsnet.org/apsstore/shopap.... Available for purchase from APS Press.

Ottman, O. & Olson, O. (2009). Growing grain sorghum in Arizona. Available at: http://extension.arizona.edu/sites/ex.... [Accessed 09 April 15]. Free to access.



Common Pests and Diseases

Smut (Covered Kernel)
Sporisorium sorghi
Sporisorium spp.

Symptoms
Head replaced by brown, powdery mass of fungal spores covered by gray to brown membrane; entire head may be affected or fungus may be localized at the top, bottom or sides of the head; plants are usually or normal height
Cause
Fungi
Comments
Disease emergence favors cool dry soils
Management
Disease can be controlled by growing resistant varieties and through the application of appropriate fungicides

Anthracnose
Colletotrichum graminicola

Symptoms
Small, circular red lesions with a distinct margin develop on leaves and stems; lesions may enalrge during humid weather conditions; plant becomes defoliated; tan spots with red margins may appear on upper parts of stems; plants may die before reaching maturity
Cause
Fungus
Comments
Disease emergence favors warm temperatures
Management
Plant resistant varieties; remove other susceptible plants e.g. Johnson grass; rotate crops; plow crop debris into soil after harvest

Charcoal rot
Macrophomina phaseolina

Symptoms
Lower stalk appears shredded and dark gray; small, black fungal structures on internal parts of the stalk giving tissues a dark gray color; pith decomposes leaving only the outer stem tissue; infected plants will usually lodge
Cause
Fungus
Comments
Damage from the disease is usually greatest in fields which are subject to drought stress
Management
Plant varieties with strong stems; plant sorghum in fertile soil and avoid overcrowding unless using irrigation; use irrigation during flowering and grain-filling to reduce drought stress; rotate crop with cotton to reduce disease severity

Gray leaf spot
Cercospora sorghi

Symptoms
Small red spots on leaves which enlarge to form rectangular lesions between leaf veins; lesions may coalesce to form stripes or irregular blotches
Cause
Fungus
Comments
Disease emergence is favored by periods of warm and wet weather during the growing season
Management
Disease can be controlled by planting sorghum varieties that or tolerant or resistant to the disease

Rough spot
Ascochyta sorghi

Symptoms
Small, oval or elongated red spots on leaves; lesions coalesce and develop hard black fungal fruiting bodies, giving the leaves a sandpaper-like texture; rough areas may become large enough to kill entire leaf
Cause
Fungus
Comments
Fungus survives between growing seasons on crop debris
Management
Sorghum varieties with a high level of resistance should be planted in areas where the disease is problematic but the disease generally causes only minor losses when present

Zonate leaf spot
Gloeocercospora sorghi

Symptoms
Concentric or zoned patches of red and purple bands separated by straw colored or tan bands on leaves; spots often occur in a semi-circular pattern along leaf margins; salmon colored spore masses may develop on lesions during periods of wet weather
Cause
Fungus
Comments
Fungus may be able to spread via infested seed; common disease of sorghum during wet weather; fungus also attacks millet speacies
Management
Losses can be reduced by rotating crop and practice of good sanitation by removing crop debris and susceptible weed species from the field