Spinach

Description

Spinach, Spinacia oleracea, is a leafy herbaceous annual plant in the family Amaranthaceae grown for its leaves which are used as a vegetable. The spinach plant has simple leaves which stem from the center of the plant and measure about 2–30 cm (0.8–12.0 in) long and 1 to 15 cm (0.4–6.0 in) across. The leaves grow in a rosette and can appear crinkled or flat. The plant produces small yellow-green flowers which are 3–4 mm (0.1 in) in diameter. The flowers produce small fruit clusters which contain seeds. Spinach is an annual and survives only one growing season and can reach 30 cm (12 in) in height. Spinach originates from ancient Persia (now Iran).


Uses

Spinach is eaten cooked as a vegetable and contains both large amounts iron, calcium, and other essential vitamins and minerals.


Propagation


Basic requirements
Spinach grows well in cool areas and can survive the first frost of temperate climates. It will germinates and grows optimally at temperatures between 4 and 16°C (40–60°F) but can withstand temperatures as low as -7C (20°F). Spinach grows best in a well draining loamy soil with a pH between 6.4 and 6.8. It is sensitive to acidic soil and if the pH is too high, adding lime is recommended. The soil temperature should not exceed 21°C (70°F).

Propagation
Spinach is propagated from seed with round seeded spinach usually being sown in early spring for a summer harvest and the prickly seeded type which is usually sown in fall for harvest in winter and spring. Seeds should be planted at a depth of 1–2 cm (0.5–1 in) leaving 33–38 cm (13-15 in) between rows. When seedlings reach about 5 cm (2 in) in height they should be thinned out to a spacing of 8–10 cm (3–4 in) between plants.

General care and maintenance
Spinach requires high levels of moisture, and if rainfall is inadequate, 2.5 cm (1 in) of water should be applied every 7–10 days. Spinach also has high requirements for nitrogen and potassium which should be provided by applying fertilizer based on the results of a soil test. Potassium poses little environmental risk and may be applied based on the results of a soil test. Timing of nitrogen applications vary by location as there is a risk of leaching during heavy rainfall. In the home garden, fertilizer is often not required as long as spinach is planted in a fertile soil.

Harvesting
Spinach leaves can be harvested as soon as they are large enough to use and may be harvested by hand or machine. Individual leaves may be harvested as required in the home garden or the whole plant can be cut. In commercial production, bunched fresh spinach is usually cut by hand. SPinach for processing may be cut by machine.



References

Anderson, C. R. Spinach. University of Arkansas Division of Agriculture. Available at: http://www.uaex.edu/publications/pdf/.... [Accessed 14 April 15]. Free to access.

CABI Crop Protection Compendium. (2010). Spinacia oleracea (spinach) datasheet. Available at: http://www.cabi.org/cpc/datasheet/51117. [Accessed 14 April 15]. Paid subscription required.


Common Pests and Diseases

Spinach crown mite
Rhizoglyphus spp.

Symptoms
Leaves deformed; small holes in newly expanding leaves; mites are tiny and transparent, living deep in the crown of the spinach plant; damage can be done to newly emerged seedlings or to older plants
Cause
Arachnid
Comments
Mite infestation is favored by soils with a high organic content and by cool, wet weather conditions
Management
Destroy crop debris immediately after harvest; application of appropriate acaricide may be required if mites are damaging and weather conditions are cool and wet

Anthracnose
Colletotrichum spp.

Symptoms
Small water-soaked spots on leaves which enlarge and turn tan or brown in color with a papery texture; if infection is severe, lesions may coalesce and cause severe blighting
Cause
Fungi
Comments
Disease emergence is favored by very wet weather; spores are spread by splashing water
Management
Only plant seed from disease-free plants; avoid sprinkler or overhead irrigation where possible, watering plants from the base to reduce leaf wetness; copper fungicides are sometimes used in the case of an epidemic but are largely ineffective at controlling the disease

Damping-off & Root rot
Fusarium oxysporum
Rhizoctonia solani
Pythium spp.

Symptoms
Poor germination rate of seeds; death of newly emerged seedlings; stunted, yellow plants, particularly lower leaves; poor growth, wilting and collapse of older plants; roots may be water-soaked and discolored brown or black; necrotic lesions may girdle tap roots
Cause
Fungus
Comments
Symptomatic plants are often found in low-lying areas of the field or garden where water accumulates; disease symptoms are similar to symptoms cuased by overwatering plants
Management
Plant spinach in well draining soils; carefully manage irrigation to avoid saturating soil; use seed that has beeen treatedd with fungicide; avoid planting spinach successively in the same location

Downy mildew (Blue mold)
Peronospora farinosa

Symptoms
Initial symptoms of the disease are yellow spots on cotyledons and leaves which enlarge over time and become tan in color with a dry texture; purple fungal growth is present on the underside of leaves; severe infestations can result in curled and distorted leaves
Cause
Fungus
Comments
Disease emergence favored by moist soil and cool temperatures
Management
Plant varieties of spinach which are resistant to the disease; application of appropriate fungicides can help to protect the plant if applied before infection begins

Fusarium wilt
Fusarium oxysporum

Symptoms
Yellowing of older leaves; plants reaching maturity early; premature death of plants; reduced seed production or death of plant before seed production takes place; vascular system of older plants may have a dark discoloration; seedlings may develop symptoms similar to damping off where cotyledons wilt and seedling dies; black lesions may be present on roots
Cause
Fungus
Comments
Fungus can survive on seed and can be spread to previously uninfested fields; disease emergence is favored by warm, acidic soil
Management
Avoid planting spinach in soils known to be infested with Fusarium or where spinach has been planted the previous year; planting early can help protect the seedlings from the disease due to lower soil temperatures which are less favorable to the pathogen; avoid water stress to plants during flowering and seed set

White rust
Albugo occidentalis

Symptoms
Yellow spots on upper side of leaves; clusters of white, blister-like pustules on underside of leaves which may spread to upper leaf surfaces in advanced stages of infection; infected plants show a loss of vigor and collapse if conditions are favorable to rapid disease development
Cause
Fungus
Comments
Disease emergence favored by cool, humid nights and mild days
Management
Some spinach varieties are more tolerant of the disease than others; where protective fungicide applications are used, appropriate cultural control methods should also be utilized to reduce the risk of the pathogen developing tolerance to fungicide

Wireworms
Aeolus spp.
Anchastus spp.
Melanotus spp.
Limonius spp

Symptoms
Death of seedlings; reduced stand; girdled stems and white heads; wireworm larvae can be found in soil when dug round the stem; larvae are yellow-brown, thin worms with shiny skin
Cause
Insect
Comments
Larval stage can last between 1 and 5 years depending on species
Management
If wireworms are known to be present in soil fallow field during summer and till frequently to reduce numbers; rotate to non-host crop where possible; avoid planting susceptible crops after a wireworm infestation on cereals without either fallowing of applying appropriate pesticide

Armyworms (Beet armyworm, Western striped armyworm)
Spodoptera exigua
Spodoptera praefica

Symptoms
ingular, 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 armyworms 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

Cabbage looper
Trichoplusia ni

Symptoms
Large or small holes in leaves; damage often extensive; caterpillars are pale green with a white lines running down either side of their body; caterpillars are easily distinguished by the way they arch their body when moving; eggs are laid singly, usually on the lower leaf surface close to the leaf margin, and are white or pale green in color
Cause
Insect
Comments
Insects overwinter as pupae in crop debris in soil; adult insect id a dark colored moth; caterpillars have a wide host range
Management
Looper populations are usually held in check by natural enemies; if they do become problematic larvae can be hand-picked from the plants; an organically acceptable control method is the application of Bacillus thuringiensis which effectively kills younger larvae; chemical sprays may damage populations of natural enemies and should and should be selected carefully

(Aphids, Peach aphid, Potato aphid)
Myzus persicae
Macrosiphon euphorbiae

Symptoms
Small soft bodied insects on underside of leaves and/or stems of plant; usually green or yellow in color, but may be pink, brown, red or black depending on species and host plant; if aphid infestation is heavy it may cause leaves to yellow and/or distorted, necrotic spots on leaves and/or stunted shoots; aphids secrete a sticky, sugary substance called honeydew which encourages the growth of sooty mold on the plants
Cause
Insects
Comments
Distinguishing features include the presence of cornicles (tubular structures) which project backwards from the body of the aphid; will generally not move very quickly when disturbed
Management
If aphid population is limited to just a few leaves or shoots then the infestation can be pruned out to provide control; check transplants for aphids before planting; use tolerant varieties if available; reflective mulches such as silver colored plastic can deter aphids from feeding on plants; sturdy plants can be sprayed with a strong jet of water to knock aphids from leaves; 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

Mosaic and other viruses
Cucumber mosaic virus (CMV)
Beet curly top virus (BCTV)
Tobacco rattle virus (TRV)
Tomato spotted wilt virus (TSWV)
etc.

Symptoms
Chlorotic leaves which may have necrotic spots, mosaic patterns or ringspots; leaves may be puckered and overall growth of plant is poor and stunted
Cause
Viruses
Comments
Transmitted by various insects such as aphids and thrips; Tobacco rattle virus is transmitted by nematodes int he soil and is not a common disease of spinach
Management
Practice good weed management around plants; insecticide applications are generally not effective at preventing the disease but can prevent secondary spread to neighboring fields