Onions

Land preparation (Onions)

• Till the top soil: 30 40 cm of top soil surface. For onion production, the soil is tilled twice and leveled at the second plowing. Normally soils are prepared before the on-set of rains.

Planting of Onions

Onion nursery establishment

• Clear the bush
• Prepare the land near water source-onions need a lot of watering
• Gather the tools and choose certified packed seeds (read the expiry date)
• Mix soils well with the compost
• Measure the bed dimensions and corners
• Heap the soil mixture and raise it to at least 30 cm high and level it
• Protect the walls with timber or banana stems or wooden logs
• Dig small straight trenches horizontally at a recommended spacing
• Carefully plant the vegetable seeds at 1-2 cm spacing (width of one finger) and cover them with a little soil
• Water the bed sufficiently
• Construct the shade to avoid wind destroying it and heavy rain drops
• Cover the soil with little grass but remove them as soon as seeds germinate
• Harden the seedlings by reducing watering rate and shade materials 1-2 weeks before transplanting.
• Also reduce the number of leaves and roots if many.

Transplanting

• About 6-8 weeks after sowing, when the seedling has a base as thick as a pencil and is approximately 15 cm tall, the seedlings are transplanted to the field. Transplanting has to be done in early morning or late afternoon to avoid negative effect of direct sunlight on young seedlings;
• Apply farm yard manure ( 20-25T/Ha) and 300 kgs of NPK/Ha. Mix the manure and fertilizer with the soil before you plant the seedlings. Six week after transplanting, apply 150Kg of Urea so as to speed up the onion growth;
• Before transplanting, the seedlings are watered with enough water to avoid damaging the root system while uprooting. The planting distance is 15cm between rows and 10cm between plants.

Crop management (Onions)

• Regularly weed the onions and remove weeds;
• Mulch onions with composted leaves and straw is highly recommended to maintain soil organic content, prevent soil borne diseases, and suppress weeds;
• Weeding is mostly done by hand, although chemical weed control is possible;
• When the onion starts showing signs of maturity, remove soils around the bulb and bend leaves to fatten the bulbs.

Common onion diseases and pests, symptoms and control (Onions)

Downy mildew

Pale spots or elongated patches on leaves; gray-purple fuzzy growth on leaf surface; leaves turning pale then yellow; leaf tips collapsing

Photo. Symptoms of downy mildew on onion (Kevin et al., 2012)

Management:

• Avoid planting infected sets;
• Rotate crops to non-Allium species for 1-2 seasons,
• 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.

• Purple blotch (Alternaria porri)

This is the most serious disease of onion, particularly when grown for seed purpose. It also attacks garlic. Disease appears during periods of persistent rain. Infestation of trips also pre-disposes plants to the disease.

Initial symptoms appear as small water-soaked lesions on leaf and seed stalk which later turns brown. As the spot enlarges, purplish zonations with purplish or red margins surrounded by yellow halo will be conspicuous. Under moist conditions, the spot is covered with brown to black spores. Affected leaves and seed stalks fall down and seeds become shrivelled.

Photo. Symptoms of purple blotch on onion

Management:

Spray Dithane M-45, Victory, etc.( 50g/20L of water/2are)

• Stemphylium blight

This is also a serious fungal disease of both onion and garlic. Symptoms appear as small yellow to orange spots or streaks on middle of leaves and flower stalks on one side.

Photo. Symptoms of Stemphylium blight on onion (Kevin et al., 2012)

Management:

Spray Victory 72WP ( 50g/20L of water/2are)

• Rust

Photo: Rust on onion

• Trips (Thrips tabaci)

Thrips are major pests of onion and garlic. Adults are one mm long and yellow brown with dark transverse bands across thorax and abdomen. Both nymphs and adults rasp epidermis of tender leaves and imbibe the oozing sap. Due to rasping of sap, numerous white specks develop. Heavily infested leaves curl up, distort and finally wither away resulting in silver top. This is more serious at flowering stage of seed crop.

Management:

Cultural practices like periodical irrigation and hoeing would reduce infestation to some extent. In severe cases, spray cypermethrin (1cc/1L of water) at 15 days interval

Harvesting of Onions

• Onions are harvested when leaves are very dry and tuber outer sheath is transparent;
• Harvesting takes place 90-150 days after transplanting,
• Up root and immediately dry;
• Keep the harvested dry onions on timber material or dry grass in a well ventilated dry store.

Post harvest management(Onions)

• Onions can stay long as long as they are properly dried and not injured in a clean cool store,
• They are not perishable and can be transported far or exported.