Onion

 

Site Selection

Onions should be grown on friable soils, which contain high amounts of organic matter and have good water-infiltration rates and good moisture-holding capacity. The soil should not be compacted, and the pH should be 5.8 to 6.6. Sandy loams and muck soils are often used for onion production. For sweet Spanish onion production, soils with low sulphur levels (below 40 ppm) are recommended.

 

Land Preparation and Formation of Beds

Prepare the field by 2 ploughings and 2 harrowing. Level and pulverize the soil to a fine texture to facilitate formation of beds. Raising beds are constructed at 0.5-meter-wide by 20 m long (maximum) by 15 cm high. Double row beds will be prepared with a distance of 20-25 cm between hills and with a hole depth of at least 3.5 cm. http://cagayandeoro.da.gov.ph/wp-content/uploads/2013/04/PRODUCTION-GUIDE-ON-BULB-ONION.pdf

 

Varieties

• Red Creole
• Red Pinoy
• Yellow Granex (Hybrid)

http://cagayandeoro.da.gov.ph/wp-content/uploads/2013/04/PRODUCTION-GUIDE-ON-BULB-ONION.pdf

 

Short day variety

Short-day onion plants require about 12 hours of daylight each day to form bulbs. Grow short-day onions during fall and winter in USDA zones 6 through 10. Plant them when temperatures range from 55 to 75 F. Short-day varieties include:

• ‘Red Burgundy’ (Allium cepa‘Red Burgundy’) produces sweet, mild, red, cooking onion bulbs that are ready to harvest 95 days after planting. The bulbs are 4 inches in diameter with red skin and white, red-tinted flesh. They stay fresh in cool storage for months, which is unusual for red onions.
• ‘Yellow Granex’, ‘Maui’, ‘Noonday’ or ‘Georgia Sweet’ (Allium cepa‘Yellow Granex’, ‘Maui’, ‘Noonday’ or ‘Georgia Sweet’) are sweet yellow onions that are similar to ‘Vidalia’ onions (Allium cepa ‘Vidalia’) but are ready to harvest sooner.
• ‘Yellow Granex’ onion bulbs are ready to harvest after 80 to 109 days while ‘Vidalia’ onion bulbs need about 160 days. ‘Yellow Granex’ bulbs appear flattened and are 3 to 4 inches in diameter.
• ‘White Granex’ or ‘Texas Sweet’ (Allium cepa‘White Granex’ or ‘Texas Sweet) produces sweet, mild, salad onion bulbs that are ready for harvest in 100 days.
• ‘Crystal White Wax’ (Allium cepa‘Crystal White Wax’) has pearl onion bulbs that can be pickled or put in soup or stew. They are ready for harvest after 60 days when they are 1 inch wide.

 

Long day variety

Long day onion plants require roughly 14 to 15 hours of daylight each day to form bulbs. Grow long-day onion plants in spring and early summer in USDA zones 3 through 7. Sow their seeds when the soil warms to 50 F. Plant sets two to four weeks prior to your area’s last average annual hard frost date in spring. Long-day varieties include:

• ‘Red Wethersfield’ (Allium cepa‘Red Wethersfield’) onion bulbs are 4 to 6 inches in diameter with a deep-maroon skin and pale, pink flesh. They are sweet and can be added to salads or used in cooking. They are ready for harvest 100 to 115 days after planting and store well.
• ‘Yellow Ebenezer’ (Allium cepa‘Yellow Ebenezer’) onion bulbs are 2 ½  to 3 inches in diameter, pale yellow, mild-flavored with crisp flesh and used in cooking. They are ready for harvest after 100 days and store well.
• ‘Snow White’ (Allium cepa‘Snow White’) produces sweet, white bulbs that grow in long- or short-day climates. They are ready for harvest after 90 days.

http://www.ehow.com/info_8614528_list-onion-varieties.html

 

Seedbed Establishment and Seed Sowing (Nursery)

Seedbed should be located in a well-drained, friable soil with good water holding capacity and high organic matter content. If soil pH is lower than 5.8, lime application is necessary at the rate of 3 tons/ha applied one month before transplanting. Land should be prepared by thorough ploughings and harrowing. Level and pulverize the soil to facilitate formation of beds (1-meter-wide and 20 m long). Prior to seed sowing, sterilize the beds by burning rice straw on top or by pouring boiling water to prevent pest and disease infestation.

Broadcast chicken manure or compost at the rate of 10 t/ha combined with 10 bags 14-14-14. Space 10-15 cm between rows and sow seeds evenly in a row at 5-6 seeds/inch with seeding depth of ½ inch. Approximately 25 grams of seeds is needed per square meter. Irrigation should be applied adequately in the field right after seed sowing. Seeds will germinate at about 7-10 days after sowing and are ready for transplanting 45 days after sowing. http://cagayandeoro.da.gov.ph/wp-content/uploads/2013/04/PRODUCTION-GUIDE-ON-BULB-ONION.pdf

 

 

Variety Selection

Bulbing of onions is primarily induced by photoperiod or day-length. Both long day and intermediate day onion varieties are recommended for in the north eastern United States. In addition, onions are classified by skin colour (red, white, brown, or yellow), taste (sweet or pungent), and shape of the bulb (round, flat, or globe).

 

Recommended onion varieties for growers in the north eastern United States.
Planting Method	Type	Variety	Days to Maturity
*indicates hybrid variety
Sets	N/A	Early Yellow Globe	90
Sets	N/A	Ebenezer	90
Sets	N/A	Southport Red Globe	90
Seeds/Transplants	Storage	Trailblazer*	103
Seeds/Transplants	Storage	Hendrix*	107
Seeds/Transplants	Storage	Fortress	110
Seeds/Transplants	Storage	Spartan Banner 80*	115
Seeds/Transplants	Storage	Vega*	125
Seeds/Transplants	Sweet Spanish	Alisa Craig	95
Seeds/Transplants	Sweet Spanish	Candy*	105
Seeds/Transplants	Sweet Spanish	Expression	105
Seeds/Transplants	Sweet Spanish	Spanish Medallion	110
Seeds/Transplants	Sweet Spanish	Exacta*	110
Seeds/Transplants	Sweet Spanish	Red Sky* (red bulb)	103
Seeds/Transplants	Sweet Spanish	Redwing* (red bulb)	115
Seeds/Transplants	Sweet Spanish	Mercury* (red bulb)	115

https://extension.psu.edu/onion-production

 

Climate:

Onion is a cool season crop. It is grown during winter and harvested before the real hot season begins. Onion can be grown under a wide range of climatic condition. But it succeeds best in mild season without extremes of heat and cold. According to Rao and Purewal (1954), it can be grown as a rained crop even at elevation of 1500 to 2000 m between April and August, Onion produce bulbs more rapidly at warm (21⁰ C to 26⁰ C) than at cool 15⁰ C to 21⁰ C) temperature.

 

Soil and its Preparation:

Onion can be grown on various soils. But sandy loam, silly loam and deep friable soils are best suited for onion crop. The land is prepared by giving 5-6 ploughings. The optimum pH range is between 5.8 and 6.5. http://agriinfo.in/default.aspx?page=topic&superid=2&topicid=935

 

Environmental Requirements for Onion Seed Production

Onion seed production is influenced not only by genetic factor but also environmental factors such as temperature, rainfall, soil conditions and presence of beneficial insects.

 

Cultivars: Seed production potential also depends on cultivars. Some onion types produce few flower stalks in the country due to their higher chilling requirement. So, producers should exercise seed production on adapted onion varieties like Bombay red, Adama red, etc. Likewise, in selecting onion varieties for seed production, emphasis should be given to the most popular varieties under production. Currently, Bombay red is the most widely grown onion variety under irrigation in the country due to its higher bulb yield and earliness. This variety is not suitable for production under rain fed as it easily rots in the field if encounters rain during maturity stage. Yields up to 400 qt for Bombay red were observed on farmer’s fields in CRV areas, which is mainly due to its tolerance to higher plant population (can successfully produce good size bulbs at spacing as low as 4cm between plants). On the other hand, Adama red can produce good size bulbs only at plant spacing greater than 6cm. Unlike the former, Adama red can be produced under rain fed conditions as it tolerates rotting due to rain effects during maturity stage. Thus, when selecting a variety for its seed.

In this regard, it is paramount important that the government extension agents and producers’ knowledge and skill be improved in the areas of seed production technology. True to type bulb selection, seed production practices, harvesting, seed processing and storage are the underlying principles in the production and supply of quality onion seed. Thus, this simplified manual that encompasses the main processes in onion seed production technology is prepared in order that higher and quality seed yields are produced and supplied to users. It also plays significant role in the maximization of profits from the intervention in seed production the yield and area coverage of that variety should also be taken in to account.

 

Temperature:

Most of the onion varieties are adapted to low and mid altitude areas (700-1800 m.a.s.l), even though onion can grow up to 2000 m.a.s.l. The ideal temperature for mother bulb production is 180 c-240 c day and 10-120 c night temperature. For bulb production it can go higher beyond these ranges. However, it is major factor for flower stalk development and seed set. Higher temperature can prevent flowering. After bulb develops, cool weather with ample moisture supply is required for flower stalk initiation. Then, drier conditions with good sunshine are required for seed maturity, harvesting and processing. It is also important to know specific requirement of the crop varieties. For instance, Bombay and Adama red can flower and produce higher seed yield under relatively lower chilling temperature while variety like Red Creole needs very low temperature and cannot produce sufficient seeds like the other varieties in the CRV and similar areas.

High temperature during flowering also results in flower abortions and hence lower seed yield. So, selection of appropriate months in a given locality is crucial in onion seed production venture. Studies and experiences show that onion seed production in the country is best if mother bulbs are planted in September and October for flowering to take place in the months of January and February- in cooler and drier months. This is the best period for getting higher and quality seed yields. This is particularly true in the Central Rift Valley (CRV) areas where this experience was developed.

 

Rainfall

During flowering, seed development and maturity excessive rainfall and very cool condition is undesirable as they lead to disease development and poor seed setting. Good sun shine at the time of full blooming stage will facilitate the activity of beneficial insects for higher rate of cross pollination and seed set. The relative humidity should be lower at the time of seed development.

 

Soils

Light soil with good fertility and drainage and pH of 6.0-8.0 is preferred for onion production. Loam or clay loam soils are best suited for seed production. http://coin.fao.org/coin-static/cms/media/7/13029380384160/onion_seed.pdf

 

Cultivation of Onion

As the onion is a shallow-rooted plant, care must be taken not to injure the roots by deep tillage. When hard rains incrust the soil before seeds have germinated, light raking or rolling will be an advantage. Horse cultivators are sometimes employed, especially in the heavier soils, which are difficult to work by hand. However, the additional spacing between rows, required for horse tillage, necessarily limits the yield. If ground has been properly prepared, there will be few instances when the rows should be more than 1 foot apart. Hand wheel hoes must then be employed in cultivating. Both single and double wheel types are in common use, but it is more economical to use double than single wheel hoes when the plants are small. Many growers prefer the single wheels at all stages of growth. Straight rows and uniform spacing are a great advantage in the operation of wheel hoes. The vertical shovels or teeth are most useful in heavy soils, while the horizontal sweeps are most serviceable in light soils. The latter attachments may be used without danger of covering the small plants. It is necessary to cultivate from 8 to 15 times during the season.

Hand weeding and thinning are required. This work is often done by boys and girls. The thinning is usually performed at the first weeding, when 8 or 10 plants are allowed to the linear foot of row, but in very good soils and when large bulbs are desired, the plants should stand about 2 inches apart. Special hand weedier are in common use. Both weeding and thinning should be avoided as much as possible by the proper preparation of the soil and the adjustment of drills. The figure below shows a well-managed onion field on Long Island.

 

 

Irrigation

In many sections of the West and the Southwest onions cannot be grown without irrigation, the ground being too dry to supply the moisture necessary. All of the Bermuda onions of the Southwest are grown under irrigation. The land is flooded before planting and afterwards at intervals of a week or 10 days until the bulbs are full sized, when water is withheld to induce ripening. An increasing number of growers in various parts of the country are employing the overhead system of irrigation, which is ideal when applied to this crop. Sprinkling before or after planting prevents the blowing of muck and sandy soils and the accompanying disastrous results in young plantations. Irrigation increases yields and insures the crop against loss from drought. http://bookdome.com/gardening/Vegetable-Gardening/538-Cultivation-Of-Onion.html#.WcUIIsiGPIU

 

Methods of Onion Seed Production

There are two methods of onion seed production. Seed to seed and bulb to seed method; both can be used in seed production. But the bulb to seed is the most commonly used method in Ethiopia. This method has a number of merits; options of selection of bulbs of good size, uniform, typical colour, free from diseases and physical damages. It produces several stalks per bulbs hence give higher seed yield. This is in conformity with CDMDP experiences where seed yields up to 20 qt/ha was obtained on farmer’s field for the variety Bombay red. The method is also good to maintain the variety identity. However, in this method it takes 10-11 1/2months to produce seed (4 – 4 1/2 months for bulb production and 6-7 months for seed set and maturity).

The seed to seed method lacks the above mentioned merits. It also produces less flower stalk per bulb. But it takes 7-8 months to produce seed.

 

Bulb to Seed Method of Onion Seed Production

Mother Bulb Production

Nursery Management

The following recommended practices should be followed in preparing beds and raising good quality seedlings.

 

Nursery site: site should be near water and with good soil condition, not planted with crops like onion, garlic, tomato etc. in the previous two seasons.

 

Seed bed: soil should be well prepared and seed bed be levelled; bed size to be of 1m width x5m length (most commonly used bed size). Bed size canalso be of 1mx10m. Types of bed can be raised, flat or sunken bed depending on soil type and moisture condition of an area. Raised bed is the most commonly used in CRV areas as it avoids risks of bed over moistening.

 

Seed treatment: treating onion seed with fungicide like Apron Star is recommended particularly in CRV areas to avoid fungal diseases like damping off.

 

Seed rate: 80-100gm/1mx5m bed (for seeds >90% germination), 3.5-4 kg/ha.

 

Spacing: seeds are drilled on the rows opened at 10cm space and 0.5-1cm depth against the bed length and slightly covered with soil.

 

Fertilizer: 100 gm Urea per bed (1mx5m) or manure should be applied during sowing.

 

Bed covering/Mulching: bed should be covered with grass (dry) at 3-5cm thickness; green or non-dried grass and broad leaved materials should never be used to cover the beds.

Grass cover removal: the grass cover is removed when seedlings emerge; best time is in the morning or late afternoon.

Bed Irrigation: the bed should be irrigated with watering-can in the morning or afternoon from sowing until two weeks after seedling emergence, then if possible better to continue same till transplanting or use furrow irrigation with care.

 

Pest control: better to apply registered fungicides like Ridomil Gold within 3-4 days after grass cover removal, then after fungicides/insecticides application depends on disease or insect appearance.

 

Preconditions and Transplanting of Seedlings

The following preparations and practices should be followed for transplanting seedlings from seed bed to fields.

Seedling stage: Age of the seedlings is important for establishment and higher final bulb yield. Seedlings are ready for transplanting at 45-55 days after sowing or when 3-4 true leaves emerge; this is just before bulb formation starts (Figure 3). If seedlings overstay on beds for more than 60 days after sowing, bulb formation starts and potential for bulb size development reduced with consequent significant yield reduction.

 

Bed irrigation: irrigate slightly seedling bed before uprooting for transplanting to avoid damage to seedlings.

 

Trimming: root or shoot trimming is not recommended when seedling is transplanted at the appropriate stage. The practice reduces the final bulb yield. Producers usually trim shoots when it gets older and taller, and also lightly trim roots to facilitate planting operation. If practiced, better to trim shoots part only or root parts very lightly; not good to trim both at one time as it reduces yield significantly.

 

Furrow/ridge preparation: the field should be prepared well and furrows opened at 40 cm distance including ridge.

 

Field pre-irrigation: better to irrigate the ridges/field just immediately before transplanting to facilitate planting operation and reduce seedling damage.

 

Transplanting/spacing: This depends up on the variety. For the variety Bombay red, strong and healthy seedlings selected is planted at 5 cm space between plants on the rows and 20 cm space between the two rows on a ridge while for variety Adama red the spacing between plants should be 6- 8cm. It is better to transplant in the morning or in the afternoon for better establishment.

 

Fertilization: The rate depends on the soil fertility of an area. 200 kg DAP all at transplanting and 100 kg Urea in split, half at transplanting and the other half at 30-45 days after transplanting is recommended for CRV areas on sandy loam soil. http://coin.fao.org/coin-static/cms/media/7/13029380384160/onion_seed.pdf

 

Pest and Disease Management

 

Description	Symptoms	Comments	Cause	Management
Black Mold (Aspergillus niger)	Post-harvest black discoloration at neck, lesions on outer scale	Wash hands after coming into contact with fungus	Fungus	Seeds to be treated with appropriate fungicide to reduce rot in mature bulbs, storing  at temperature below 15 degree Celsius reduces mold from spreading, avoid bruising bulbs
Botrytis leaf blight (Botrytis Squamosa)	Small white lesions with light green halos which may slightly expand as they age	Disease emergence favours high humidity and warm temperatures, older leaves are susceptible to blighting than younger leaves	Fungus	Allow at least 30 cm spacing between plants to promote good air circulation and quick drying of foliage after rain, appropriate fungicide sprays also required
Downey mildew (Peronospora destructor)	Pale and elongates patches on leaves, leaves turning pale then yellow	Disease emergence favoured by cool temperature and leave wetness	Fungus	Plant in well-draining areas and don’t over crowd plants, avoid infected plant sets, apply appropriate fungicide and destroy infected crops
Fusarium basal plate rot (Fusarium Oxysporum)	Necrosis begins at leaf tips and move downwards, Wilting plants, infected bulbs may be brown and watery with rot spreading from stem plate to basal leaves	Disease emergence favours moderate to high temperatures	Fungus	Rotate with non-susceptible crops for at least 4 years, plant resistant onion varieties
Pink Root (Phoma terrestris)	Pink roots which darken and turn purple, roots become transparent and water soaked	Fungus colonizes through root tips, fungus can survive in soil down to a depth of 17.7 inches	Fungus	A rotation of 3 to 6 years  is preferred, plant more resistant varieties, fumigation can help reduce the pathogen in the soil
Purple Blotch (Alternaria porri)	Severely infected foliage may die, large lesions may coalesce and girdle leaf, killing any tissues between the lesions and leaf tip	Disease emergence favoured by wet foliage, with sporulation occurring in night period on high humidity	Fungus	Fungicides are effective at controlling the diseases but should be rotated for optimal control, Cultural controls includes long rotation and the reduction of leaf wetness by planting in well – drained soil and timing irrigation
Pythium seed rot (Pythium irregular)	Seeds water soaked and decomposing, seedlings that have already emerged prior to infection collapse and die	Disease emergence favours high soil moisture and cool temperatures	Fungus	Can be controlled by minimizing moisture, treat seeds with appropriate fungicides prior to planting
Fusarium damping-off (Fusarium oxysporum)	Rotting seeds, discoloured root tips which may be  pink, tan , yellow , red or black	Fungus survives in soil and emergence is favoured by moist to wet soil	Fungus	Plant only disease free seed, treat seed with fungicide, rotate crops to reduce the levels of pathogen in soil
White rot (Sclerotium cepivorum)	Older leaves yellowing, stunned growth, fluffy white growth on  base of  bulb which spreads up bulb to storage leaves	Fungus can survive in soil for 20 years and is one of the most damaging diseases of Allium crops worldwide	Fungus	Fungicides along with cultural methods recommended, treat seeds with hot water prior to planting, use long term rotation with non-allium crops
Smut (Urocystis colchici)	Dark, thickened areas on cotyledons which may become large and causes leaves to bend downwards, lesion mature and become covered in black powdery fungal masses, plant growth stunted	Smut can persist in soil for many years and is mainly introduced through infected seeds and transplants	Fungus	No resistance to disease known in onion, plant only healthy seeds and transplants – if smut is present in the soil they will not become infected
Leaf streak and bulb rot (Pseudomonas Viridiflava)	Dark green oval lesions or streaks on leaves, reddish brown discoloration of inner scales, rot developing in ring like pattern	Greatest damage occurs during winter, rapid spread of disease on infected plants  is promoted by rainfall	Bacterium	Avoid fertilizing during winter, apply appropriate bactericidal sprays
Onion yellow dwarf Onion yellow dwarf virus ( OYDV)	Yellow streaks on bases of first leaves, leaves may be flattened or crinkled, flower stalks yellow and twisted	Transmitted by several aphids, including peach aphid, virus is not spread via seed or pollen	Virus	Plant more tolerant varieties, remove infected plants, to certain extent insecticides can be used to control aphids, planting sets or transplants which were produced in area free of virus
Thrips (Thrips tabaci Frankliniella occidentalis)	Distorted tissues, scarring of leaves, infected plants may have a slivery appearance	Most damaging at the initial stage of bulb development	Insect	Predatory mite, pirate bugs and lacewings are natural enemies, avoid planting onion in close proximity, apply appropriate insecticides, overhead irrigation can helps to reduce thrips
Rust (Puccinia Porri)	Small white flecks on leaves and stems which develop into circular or elongated orange pustules, severe infestations can cause leaves to yellow and die	Favours high humidity and low rainfall	Fungus	No resistance, apply appropriate protective fungicide
Leafminers (Lyriomyza spp.)	White and winding trails on leaves, early infestation can cause yield to be reduced	Mature larvae drop from leaves into soil to pupate, entire lifecycle can take less than 2 weeks in warm weather, insect may go through 7 to 10 generations  per year	Insects	Check for leafminers before planting, remove plants from the soil after harvest,  use appropriate insecticide whenever required.
Onion Maggot (Delia antiqua)	If infestation occurs during bulbing, bulbs will be deformed and susceptible to storage rots after harvest, stunted or wilting seedlings, adult insect lay eggs around the base of plant and the larvae that emerge are tiny and bore into onion plant	Females can lay hundreds of eggs during their  2 to 4 week life span	Insect	Can be managed by good sanitation and appropriate insecticide.
Bulb Mites (Rhizoglyphus spp. Tyrophagus spp.)	Stunted plant growth, bulbs rotting, pest is a cream – white, bulbous mite which resemble pearl with legs	Damage by bulb mites allow secondary invasion by other pathogens and causes bulb rots	Arachnid	Don’t plant successive crops of onion or garlic in same location, allow fields to fallow to ensure that any residual organic matter decomposes completely because crop residues harbor mite population

http://www.academicjournals.org/article/article1412855249_Mishra%20et%20al.pdf

 

Harvesting Onion

When the bulbs are to be stored they will keep better if allowed to become fully ripe before pulling. Figure 93 illustrates a field of onions in ideal condition for harvesting; the tops are dead and shrivelled and the outer skin of the bulbs dry. While full ripeness is highly desirable, other factors should be considered: There is danger of second growth, especially if there is much rain; better prices for the early crop may be an inducement to gather part or all of the crop sooner than if the bulbs are to be stored; when there are large areas to harvest it is necessary to start in ample time in order to complete the work while weather conditions are favourable and before there is loss from rain. Harvesting is often begun when most of the tops have merely turned yellow. Early pulling in the North is especially important for bulbs of foreign types. August and September are the busy harvesting months in the North, and March and April for the Bermuda crop in the South.

It is the universal custom to partially dry or cure the crop in the field. After removing the bulbs by hand or with a plough, if they are covered with soil, 8 or 10 rows of onions are thrown together into windrows, allowed to remain undisturbed for a few days and then stirred occasionally with a wooden rake to facilitate drying. White bulbs are quickly injured by exposure to sun and rain, so that these must be cured under some kind of cover. Topping is usually done in the field after the bulbs are ready for storage, the tops being twisted off by hand or cut with sheep shears. Extensive growers sometimes use topping machines, which also grade and deliver the bulbs in bags or crates. The curing process is continued in sheds, cribs or other suitable houses until the bulbs are ready for permanent storage.

http://bookdome.com/gardening/Vegetable-Gardening/538-Cultivation-Of-Onion.html#.WcUIIsiGPIU