By MN Reporter

Bulb onions, also known as Kitunguu Maji has a ready market in Kenya with immediate market which is yet to be satisfied with imports from Tanzania accounting to 50 per cent of cnsumption.

The most profitable onion is the bulb with homes preferring mid-size bulbs compared to larger ones for hotels and institutions, so a farmer should know the type for market.

Onions are particularly high in vitamin C with several seed varieties in the country, as a farmer can seek from the nearest agrovet with these types available: Red Creole, Bombay Red, Red Star F1,Texas Early Grano, Neptune F1 and Tropicana F1 among others.

Onion takes 90 days to mature and can grow in a variety of climatic conditions and soil characteristics which are well-drained soils.

Onion Yields per Acre

• Red Pinoy- Up to 30 tonnes per acre.
• Bombay Red- Up to 16 tonnes per acre.
• Red Creole- Up to 16 tonnes per acre.
• Texas Early Grano- Up to 21 tonnes per acre.  

Land Preparations

The nursery bed should be a meter above ground and filled with manure placed under a shade from direct sunlight. Rows of 15cm apart and insertion of 1cm with mulch applied. Seeds start to germinate from 7-10 days.

The onion seed rate ranges from 0.8-1.2kg per acre. Seedlings are transplanted 6-8weeks after sowing or when your onions have produced three to five well-formed leaves, and its base is pencil thick.

Before transplanting follow these guidelines:

• Reduce the rate of watering to make seedlings stronger in terms of structure.
• Remove the shade cover to get the seedlings more used to stronger sunshine.
• Transplant early in the morning or late in the evening away from scorching sun.
• Transplant your seedlings in 2.5-3cm deep trenches at a spacing of 30cm between rows and 8-10cm between plants.
• Firm up the seedling with the surrounding soil.
• Cut off 50% of green tops to hasten your onion take off.

Fertilizer Use

Before planting, you should apply 10-16tonnes of well-decomposed manure per acre laced with 0kg of TSP to the fertilizer and incorporate it into the soil. Thirty days later top-dress your onions at a rate 40kg of CAN per acre. The second topdressing should be done 45days after transplanting at the rate of 80kgs of CAN per acre.

This should be done before the onions start forming bulbs with care taken as too much nitrogen will result in the formation of thick necks.

Irrigation and disease control

Onions require light and frequent irrigation depending on the type of soil you have grown your onions in. Lighter soils such as sand will require more frequent water applications, but less water applied.

Onions require just enough moisture during the growing stage. At the bulbing stage, the onions will require a substantial amount of water. You should reduce the watering towards the maturity stage.

You should take care not to over irrigate your crop as excessive moisture encourages the spread of fungal diseases. Also, water stress will cause the bulbs to split or form multiple bulbs in one plant. 

Diseases Affecting Onions

Onion diseases can result in considerable losses in terms of the quality and quantity of your produce. It is essential to quickly identify any disease attacks and mitigate them before the disease spreads all over your farm. Some of the conditions that attack onions include;

Purple Blotch– A fungus causes this disease. It appears as small white spots on the foliage and spreads rapidly under moist conditions. A severe attack is indicated by the appearance of large purplish blotches surrounded by yellow to orange border. This infection can spread to the onion bulb where it may cause a wet orange spot starting from the neck. To control purple blotch, you should;

1. Use recommended spacing to ensure proper drainage of the field

2. Spray fungicides such as Mancozeb (Dithane M45®) to the crop to control the spread.

3. Use resistant varieties such as Red Pinoy.

Rust– A fungus causes this disease. It is prevalent in high humidity, high temperature, and densely populated farms. It appears as small reddish dusty spots on the leaves. Heavily infected leaves turn yellow and die. To control rust, you should;

1. Practice crop rotation.

2. Practice recommended crop spacing and nutrition.

3. Spray fungicides to control the spread of the disease.

Neck rot– This disease is caused by a fungus which enters the bulb through cracks in the flesh. It appears as a dark brown patch on the top part of the bulb during storage. To control neck rot, you should;

1. Dry the bulbs thoroughly after the harvest.
2. Use fungicide treated seeds.
3. Store only bulbs with dried out and thin necks.
4. Avoid using high nitrogen fertilizers.

Pests affecting Bulb Onions

Pests cause a lot of losses in terms of quality and quantity of the crop. Onions are attacked by a variety of pests the most common being;

Onion flies– They appear as white cream in colour. Onion flies cause damage as they eat the lateral roots causing tunnels into the taproot, plants become shriveled or eventually die. They are controlled by; 

1. Practicing crop rotation 

2. Practicing field sanitation by destroying infested plants.

3. Using well-decomposed manure.

Onion thrips– They are small, slender winged insects that attack the leaves. Both its nymph and adult attack the leave within the leave sheaths. Infested leaves have silvery sunken patches. When the infestation is severe, the infected leaves wither and dry up. You can control onion thrips by;

1. Use of insecticides

2. Maintaining proper irrigation levels to keep plants from being vulnerable to attack.

3. Ensuring proper weeding is done on the farm.

Leaf miners– They are small black and yellow flies which lays its eggs on the leaf. The eggs will then hatch and feed on the leaf interior, leaving thin, white winding trails on the leaves. This may result in leaves dropping from the plant prematurely. You can control leaf miners by;

1. Removing plants from the soil immediately after harvest
2. Spraying with insecticide.

Weed Control

There are many ways weed control can be done while farming onions in Kenya. Common weeds that grow alongside onions are Mexican marigold, star grass, sow thistle and thorn apple. Some of the weed control methods include;

• Hand pulling-You can manually extract the weeds by pulling them by hand and burning them before they flower.
• Chemical method- You can use herbicides such as Catapult 480SL and Predator 340EC to control the weeds. Use of chemicals is cost-effective and is also easy and fast to apply. Spraying will only target the weeds meaning there will be no mechanical damage to the crop. 
• Weeding- You can employ the use of a hoe to dig out weeds as they emerge. Weeding should be done carefully to avoid damaging your plants. 

Intercropping onions

Intercropping is essential in ensuring you maximize your returns from your farm. It also has other benefits such as controlling pests such as caterpillars in vegetative plans. You can intercrop onions with other crops such as kales, lettuce and cabbages to deter caterpillar attacks on the leaves of the vegetative plants.

Onions have also shown the capability of repelling insects on strawberry and peach plants. Other crops that can be planted alongside onions include beets and parsnips.

Care should be taken not to overcrowd the farm so as not to affect the drainage of the farm and to control the spread of fungal diseases.

Harvesting and Post-Harvest

Onions usually become ready for harvesting at around 120 to 150 days after transplanting. You should harvest your bulb onions when 75 % of the tops of the crop have dried and fallen over. The onions are harvested by pulling and leaving the bulbs on the soil surface to begin the process of curing.

Post-harvest Care for Bulb Onions

Post-harvest care of onions involves the process of curing. Curing is whereby you dry the neck and outer leaves of the bulb. This prolongs the shelf life of the bulb by preventing moisture loss and attack by diseases. Curing can either be protected or done in the field.

Field Curing

Field curing is only possible in cases when you have harvested your crop in the dry season. Field curing is done by placing the harvested onions in rows in the field with leaves partially covering the bulbs to prevent sunburns. You should allow the neck to dry completely. This can take up to 3 weeks to fully cure.

Protected curing.

You can practice this when the weather does not allow for field curing. Curing is done in a warm, dry ventilated environment away from the rain. Protected curing involves the removal of excess soil from the roots and trimming the foliage leaving 2.5cm of a section of stem at the neck. The onions should be placed in a single layer and let to cure until the necks completely dry. 

Sorting Bulb Onions

You need to sort your onions so as to be able to have good quality onions. The following onions should be sorted out:

• Onions with double or small bulbs. 
• Onions that are decaying
• Onions that have thick necks
• Onions that have injuries
• Onions that have bolted. 

These, except the decaying ones, might fetch some proceeds at low prices, but will not store well.

Grading Bulb Onions 

Grading for bulb onions is done before and after storage. For the local market the onion grades are:

1. Large onions
2. Medium-sized onions
3. Small onions

Packaging bulb onions

Onions in Kenya are usually packaged in Onion nets.