Artichoke

Description

The globe artichoke, Cynara scolymus, is an herbaceous perennial thistle in the family Asteraceae grown for its edible fleshy flowerhead, or heart, which is considered a delicacy. The globe artichoke has arched, irregularly lobed leaves which are silvery green in color, reaching 50–82 cm (19.7–32.3 in) in length and possessing a few spines. The flowerhead is 4–8 cm (1.6–3.1 in) in diameter with numerous triangular scales and individual florets which are purple in color. Artichokes mature in 150 to 180 days after sowing and can reach heights of 1.4–2 m (4.6–6.6 ft). The globe artichoke may also be referred to as leaf artichoke, artichoke, artisjok, artichaut, carciofo, alcachofra, alacachofa or kharsuf and it originates from Southern Europe and the Mediterranean.


Uses

Artichokes are grown primarily for consumption and can be eaten raw or cooked. Globe artichokes may also be canned or pickled or processed to make tea, liqueur or for extraction of secondary metabolties such as cynarin and chlorogenic acid which can be used in the preparation of alcoholic beverages. The globe artichoke has one of the highest antioxidant contents of any vegetable and is therefore valued as a health food with roles in lowering cholesterol and regulating blood sugar levels.


Propagation


Basic requirements
Globe artichokes are cool season crops and grow best in deep, fertile and well drained soils with a pH between 6.0 and 8.0. The prevailing climatic conditions are extremely important to successful growth of high quality flowerheads. The optimum daytime temperature is 20–22°C (68–71.6°F) and optimum nighttime temperature is 12–14°C (53.6–57.2°F). The plants will tolerate both cold and high temperatures but this will reduce the tenderness of the head. Frost can cause the flower heads to blister and may kill the buds. In addition, globe artichokes require frequent irrigation to ensure growth of good quality heads. However, the plants will not tolerate a waterlogged soil.

Propagation

Vegetative propagation
Globe artichokes are usually vegetatively propagated from underground shoots known as 'ovoli' or from the suckers, stumps or dried shoots from the previous growing season although it can be grown as an annual plant from seed. Existing globe artichoke plants should be divided in Fall or Winter when the plant is dormant. Shoots should be selected from plants that produce well and should be removed when they are about 20 cm (8 in) in height. The shoots are removed by cutting the attachment to the mother plant at the root with a sharp knife and gently loosening it from the soil and existing root ball. The separated shoots should be planted in a freshly prepared bed. The roots should be set to a depth of 15 to 20 cm (6-8 in) and spaced 1.2 to 1.8 m (4-6 ft) apart. Do not harvest any flower heads in the first year while the new plants establish.

Seeds
Globe artichoke seeds should be started indoors approximately 2 month prior to the last frost date for your area. Seeds should be sown 2.5 cm (1 in) deep in seeds starting mix in small 4 in pots. Seeds should be sown generously as successful germination is approximately 70% and not all of the emerging seedling will produce high quality plants. Seedlings should be transplanted outdoors after hardening and after all danger of frost has passed. Space the plants 0.9 m (3 ft) apart in rows spaced 0.9 m (3 ft). AFter the first year, remove any plants that are not producing well to achieve a final spacing of 1.2 to 1.8 m (4-6 ft) between plants.

Harvest
Globe artichoke flower buds should be harvested before they begin to open. Small, immature heads are more tender than older heads close to opening. Use a sharp knife to cut the buds from the plant leaving a 2.5 to 7.5 cm (1-3 in) section of stem with each bud. Once all buds have been harvested from the plant, the plant should be cut down to the ground.

General care and maintenance
Globe artichokes will benefit from the application of a balanced fertilizer once every month during the growing season. Plants should not be allowed to dry out and soil should be kept moist. A covering of thick mulch will help to conserve soil moisture. Remove the mulch when the plants begin to bud and replace with a generous covering of compost. After harvest, cut the stems of the plant back to ground level or slightly below the soil line. Protect the plants over winter by mulching over the roots with plenty organic mulch (e.g. about 20cm/8 in of straw and/or leaves). this protective layer can be supplemented by further covering the plants with a cardboard or styrofoam box filled with straw and leaves.


References

CABI Crop Protection Compendium. (2011). Cynara cardunculus var. scolymus datasheet. Available at: http://www.cabi.org/cpc/datasheet/17585.. [Accessed 05 November 14]. Paid subscription required

Drost, D. (2010). Artichoke in the garden. Utah State University Cooperative Extension. Available at: http://extension.usu.edu/files/public.... [Accessed 05 November 14]. Free to access

Maynard, A. A. & Hill, D. E. How to Grow Globe Artichokes in Connecticut. The Connecticut Agricultural Experiment Station. Available at: http://www.ct.gov/caes/lib/caes/docum.... [Accessed 05 November 14]. Free to access


Common Pests and Diseases

Spider mites (Two-spotted spider mite)
Tetranychus urticae

Symptoms
Leaves stippled with yellow; leaves may appear bronzed; webbing covering leaves; mites may be visible as tiny moving dots on the webs or underside of leaves, best viewed using a hand lens; usually not spotted until there are visible symptoms on the plant; leaves turn yellow and may drop from plant.
Cause
Arachnid
Comments
Spider mites thrive in dusty conditions; water-stressed plants are more susceptible to attack.
Management
In the home garden, spraying plants with a strong jet of water can help reduce buildup of spider mite populations; if mites become problematic apply insecticidal soap to plants; certain chemical insecticides may actually increase mite populations by killing off natural enemies and promoting mite reproduction.

Bacterial crown rot
Erwinia chrysanthemi

Symptoms
Stunted plant growth; wilted leaves in high temperatures; plant collapse; new leaves do not expand and turn brown and dry; crown tissue becomes soft and rots; black discoloration when cross-section of stem taken.
Cause
Bacterium
Comments
May be spread by cutting tools; digging and splitting crowns may cause new plantings to become infected.
Management
Do not use infected crowns as planting material; start plants from seed or disease free transplants.

Botrytis rot or gray mold
Botrytis cinerea

Symptoms
Crown of plant slimy and foul smelling; fuzzy white to gray mold present.
Cause
Fungus
Comments
More prevalent when rainfall is high.
Management
Plant in light, well-draining, fertile soils; avoid overcrowding plants and planting seeds too deeply; do not wet foliage when watering, water plants at base; remove crop debris from soil after harvest.

Artichoke aphid
Capitophorus elaeagni

Symptoms
Leaves curling and turning yellow; reduced plant growth; small, deformed buds; stalks cannot support weight of buds and droop; sooty mold growing on plants due to honeydew deposits secreted by insect; insect is small, soft-bodied and pale green to yellowish green in color.
Cause
Insect
Comments
Symptoms occur when aphid numbers are large; insects should be visible on underside of leaves; become more problematic in high temperatures and humidity.
Management
Destroy plant immediately after harvest to prevent population spread; wash aphids from plants with a strong stream of water; insecticidal soaps or oils such as neem or canola oil are effective organically acceptable methods of control.

Artichoke plume moth
Platyptilia carduidactyla

Symptoms
Holes in leaves and stems which are discolored black and filled with frass (insect excrement).
Cause
Insect
Comments
More of a problem when growing artichoke as a perennial.
Management
Pick all infested buds at harvest and destroy; cut plant stems above ground, shred plants and incorporate into soil; apply Bacillus thuringiensis or insecticide.

Armyworms (Beet armyworm, Yellow striped armyworm)
Spodoptera exigua
Spodoptera ornithogalli

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 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.

Loopers (Cabbage looper, Alfalfa looper)
Trichoplusia ni
Autographa californica

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.

Flea beetle (Palestriped flea beetle)
Systena blanda

Symptoms
Small holes or pits in leaves that give the foliage a characteristic “shothole” appearance; young plants and seedlings are particularly susceptible; plant growth may be reduced; if damage is severe the plant may be killed; the pest responsible for the damage is a small (1.5–3.0 mm) dark colored beetle which jumps when disturbed; the beetles are often shiny in appearance.
Cause
Insects
Comments
Younger plants are more susceptible to flea beetle damage than older ones; older plants can tolerate infestation; flea beetles may overwinter on nearby weed species, in plant debris or in the soil; insects may go through a second or third generation in one year.
Management
In areas where flea beetles are a problem, floating row covers may have to be used prior to the emergence of the beetles to provide a physical barrier to protect young plants; plant seeds early to allow establishment before the beetles become a problem - mature plants are less susceptible to damage; trap crops may provide a measure of control - cruciferous plants are best; application of a thick layer of mulch may help prevent beetles reaching surface; application on diamotecoeus earth or oils such as neem oil are effective control methods for organic growers; application of insecticides containing carbaryl, spinosad, bifenthrin and permethrin can provide adequate control of beetles for up to a week but will need reapplied.

Artichoke curly dwarf virus
Artichoke curly dwarf virus (ACDV)

Symptoms
Plant growth reduced; plant lacking vigor; leaves may be distorted with dark necrotic spots and/or patches; deformed buds
Cause
Virus
Comments
Currently not known how virus is spread; use disease free crowns to propagate or certified seed
Management
Use only certified planting material; remove and destroy infected plants to limit spread