Garlic

Description

Garlic, Allium sativum, is a an herbaceous, annual, bulbous plant in the family Amaryllidaceae grown for its pungent, edible bulb of the same name. The garlic plant can either have a short, woody central stem (hardneck) or a softer pseudostem made up of overlapping leaf sheaths (softneck). Hardneck varieties produce a false flower stock which is termed a 'scape' and produce larger garlic cloves but in smaller numbers. Softneck garlic is the most popular variety of garlic grown in the US. The bulb can be up to 7 cm (2.8 in) in diameter and is made up of 1–15 cloves. The stem is very short and flattened and gives way to a pseudostem, The garlic plant can possess 6–12 flat, blade-like leaves which can stretch up to 50 cm (19.7 in) long. The plant can reach 60 cm (23.6 in) in height and is an annual, surviving only one growing season. Garlic is believed to originate from Asia.


Uses

Garlic is primarily used for flavoring food and can be dried, ground or powdered for this purpose


Propagation


Basic requirements
Garlic is a hardy perennial which can be grown in a variety of soil types. The plants perform best when planted in a light, well draining, organic loam with a pH between 6.0 and 7.0. The plant grows well in cool weather but will tolerate a range from 9–28°C (48.2–82.4°F). Garlic should be planted in an area that receives full sun for most of the day. Garlic requires a period of cold followed by a period of light and heat in order to develop properly. The plants will perform best when they have 6-8 weeks below 4.4ºC (40ºF). It may be beneficial to chill bulbs prior to use if planting in area that does not fulfil these temperature requirements.

Planting
Most garlic varieties do not produce fertile seed so the plant is propagated from the cloves. Individual cloves are obtained by breaking apart the bulb. Generally, garlic should be planted in the Fall around the same time spring bulbs such as daffodils are planted. Planting in the Spring does not allow sufficient time for the roots system to develop and the garlic may not form heads. The soil should be prepared for planting by digging with a fork to loosen it and break up any large clumps. Cloves should be planted 5–8 cm (2-3 in) deep, leaving 8–10 cm (3.1–3.9 in) between individual plants and 15–20 cm (5.9–7.9 in) between rows. The cloves should be planted pointed side up with the basal plate positioned downwards. The roots will grow from the basal plate. Each clove will produce a whole head of garlic which can be harvested and cured before use.

General care and maintenance
When the ground begins to freeze, it is good practice to cover the garlic plants with a layer of straw mulch. This helps to protect the plants over winter, prevents frost heaving and helps to suppress weeds in the Spring. Garlic requires additional irrigation during dry periods but watering should be ceased a few weeks prior to harvest to allow the papery skin around the bulb to dry and to prevent the development of disease. Garlic benefits from the addition of fertilizer during the growing season. Nitrogen should be applied in early Spring, later applications may delay bulb development. Hardneck garlic should be pruned when the flowering stalks (scapes) begin to straighten. Removal of the flower head directs the plants energy to bulb production. Softneck garlic does not require pruning.

Harvesting
Garlic is ready to harvest when the plants begin to turn yellow or brown and begin to fall over. Dig the plants while there are still some green leaves remaining on the plant. Harvest the bulbs by digging the plant carefully and lifting the bulbs using a fork. The garlic can be used straight away or it can be cured for longer storage. Garlic can be cured by hanging the plants in bunches or by spreading them out on a rack or screen. The plants should be kept intact while they cure, do not remove the tops until the garlic is dry. Curing should be carried out in a cool, dry place with good ventilation such as a barn, attic or garage. Once dry, the bulbs will keep for up to a year.


References

CABI Crop Protection Compendium. (2010). Allium sativum datasheet. Available at: http://www.cabi.org/cpc/datasheet/4250. [Accessed 08 December 14]. Paid subscription required.

Meyers, M. (2006). Garlic. An Herb Society of America Guide. The Herb Society of America. Available at: http://www.herbsociety.org/factsheets.... [Accessed 08 December 14]. Free to access.

Schwartz, H. F. & Mohan, S. K. (Eds.) (2008) Compendium of Onion and Garlic Diseases and Pests.Second Edition. American Phytopathological Society Press. Available at: http://www.apsnet.org/apsstore/shopap.... Available for purchase from APS Press.

Sideman, B. (2011). Growing Garlic. University of New Hampshire Cooperative Extension. Available at: https://extension.unh.edu/resources/f.... [Accessed 08 December 14]. Free to access.


Common Pests and Diseases

Bulb mites
Rhizoglyphus spp.
Tyrophagus spp.

Symptoms
Stunted plant growth; reduced stand; bulbs rotting in ground or in storage; pest is a cream-white, bulbous mite <1 mm in length, which resembles a pearl with legs
Cause
Arachnid
Comments
Damage to plants by bulb mites allows secondary invasion by other pathogens and can cause bulb rots
Management
Do not plant successive crops of onion or garlic in same location; allow field to fallow to ensure that any residual organic matter decomposes completely - crop residues can harbor mite populations; treating garlic seed cloves with hot water prior to planting may help reduce mite populations

Purple blotch
Alternaria porri

Symptoms
Small water-soaked lesions lesions on leaves or stalk with white centers; which enlarge to become zonate and brown to purple in color with red or purple margin surrounded by yellow zone; large lesions may coalesce and girdle leaf, killing any tissue between the lesions and the leaf tip; severely infected foliage may die
Cause
Fungi
Comments
Disease emergence favored by wet foliage, with sporulation occuring during the night during periods of high humidity
Management
Cultural controls include long rotations with non-hosts and the reduction of leaf wetness by planting in well-draining soil and timing irrigation to allow plants to dry adequately during the day; some fungicides are effective at controlling the disease but should be rotated for optimal control

White rot
Sclerotium cepivorum

Symptoms
Older leaves yellowing; stunted growth; death of all leaves; fluffy white growth on base of bulb which spreads up bulb to storage leaves
Cause
Fungus
Comments
Once disease is established the field is unusable for garlic production; fungus can survive in soil for 20 years and is one of the most damaging diseases of Allium crops worldwide, causing major crop losses
Management
Fungicide treatment may not be effective at controlling white rot under conditions which are favorable to the fungi's development and control may have to rely on cultural methods: avoid transferring soil or plant material between sites; treat seeds with hot water prior to planting; use a long term rotation with non-allium crops; apply appropriate fungicides if available

Rust
Puccinia porri

Symptoms
Small white flecks on leaves and stems which develop into circular or elongated orange pustules; severe infestations can cause leaves to yellow and die
Cause
Fungus
Comments
Favors high humidity but low rainfall; spores can be transported over long distances by wind
Management
No resistance known; use only disease-free seed and plant in well-draining soil; control weeds around crop; apply appropriate protective fungicide

Downy mildew
Peronospora destructor

Symptoms
Pale spots or elongated patches on leaves; gray-purple fuzzy growth on leaf surface; leaves turning pale then yellow; leaf tips collapsing
Cause
Fungus
Comments
Disease emergence favored by cool temperatures and leaf wetness
Management
Avoid planting infected sets; rotate crops to non-allium species for 3-4 years; plant in well-draining areas and do not overcrowd plants; destroy all infected crop debris; apply appropriate foliar fungicides taking care to apply thoroughly to waxy leaves

Thrips (Onion thrips, Western flower thrips)
Thrips tabaci
Frankliniella occidentalis

Symptoms
Discolored, distorted tissue; scarring of leaves; severly infected plants may have a silvery appearance; insect is small (1.5 mm) and slender and best viewed using a hand lens; adult thrips are pale yellow to light brown and the nymphs are smaller and lighter in color
Cause
Insect
Comments
Onion thrips and western flower thrips have an extensive host range and can be introduced to garlic from other plants
Management
Natural enemies include some species of predatory mite, pirate bugs and lacewings; avoid planting onion in close proximity to grain fields as thrips populations build up on these plant in the spring; overhead irrigation of plants may help reduce thrips numbers; apply appropriate insecticides at first sign of thrips damage

Onion maggot
Delia antiqua

Symptoms
Stunted or wilting seedlings; plant will commonly break at soil line if an attempt is made to pull it up; if infestation occurs when plants are bulbing, bulbs will be deformed and susceptable to storage rots after harvest; adult insect is a greyish fly which lays white, elongate eggs around the base of the plant; the larvae that emerge from the eggs are tiny and white and bore into the plant; mature larvae are about 1 cm (0.4 in) long with feeding hooks
Cause
Insect
Comments
Females can lay several hundred eggs during their 2-4 week lifespan; insect overwinters as pupae in the soil
Management
Management of onion maggots is heavily reliant on good snaitation; all onion bulbs should be removed at the end of the season as maggots will die without a food source; commercial onion growers must often rely on the application of appropriate granular insecticides and, in some cases, insecticide sprays are also required; home gardeners should try to remove any volunteer wild onion and chive plants as these can act as an infection source; floating row covers may help to protect plants and prevent females from laying eggs around plants

Leafminers
Lyriomyza spp.

Symptoms
Thin, white, winding trails on leaves; heavy mining can result in white blotches on leaves and leaves dropping from the plant prematurely; early infestation can cause yield to be reduced; adult leafminer is a small black and yellow fly which lays its eggs in the leaf; larvae hatch and feed on leaf interior
Cause
Insects
Comments
Mature larvae drop from leaves into soil to pupate; entire lifecycle can take as little as 2 weeks in warm weather; insect may go through 7 to 10 generations per year
Management
Check transplants for signs of leafminer damage prior to planting; remove plants from soil immediately after harvest; only use insecticides when leafminer damage has been identified as unnecessary spraying will also reduce populations of their natural enemies

Lesion nematode
Pratylenchus penetrans

Symptoms
Stunted plants; root system lacks fine roots; round or irregular lesions on roots
Cause
Nematode
Comments
Lesion nematode has one of the widest host ranges of any nematode; nematode enters the plant through the root epidermis and consumes cell contents
Management
Hot water dips can be used to control nematodes in bulbs; crop rotation is not usually very effective at controlling lesion nematodes due to its extensive host range

Mosaic
Garlic mosaic virus (GarMV)

Symptoms
Mosaic patterns on leaves; chlorotic mottling or streaks on leaves; stunted plant growth and reduced bulb size
Cause
Virus
Comments
Transmitted by aphids; infections can be latent and produce no symptoms; infection in garlic are often found alongside other viruses such as onion yellow dwarf
Management
Plant virus-free cloves that were produced from meristem tip culture in virus-free conditions