Okra (Hibiscus esculentus) is valued for its edible green seed pods. It is rarely eaten as is, except when fried with a meal; a small quantity is usually cooked with other vegetables or added to soups and stews.
Okra grows best in well-drained, sandy loam soils. A poorly drained soil may cause the plant to drown. Okra is highly sensitive to soils with a hardpan: soil compaction can severely restrict plant growth.
The optimal soil temperature for growth is 24°C to 32°C, and the minimum soil temperature is 18°C. Damping off (seed rot) and seed decay are likely to occur at a soil temperature below 21°C.
Turn the soil after the harvest in autumn and early spring. This will expose overwintering insects to frost, killing them, and bring weed seeds to the surface to germinate. The weed seedlings will be destroyed when you disc the soil before planting, thereby reducing chemical use and saving on labour for weeding.
Recommended row spacing is 71cm to 96cm, with 20cm to 30cm between plants in the row. Treat the seeds to reduce damping off and plant them 2cm to 5cm deep. The recommended seeding rate is four to six seeds per 30cm.
When the plants are 8cm tall, thin them out so that they are 20cm to 30cm apart. Between 5kg and 6kg of seeds are required to plant 1ha. If a precision planter is used, plant at a rate of 3kg/ha.
Okra has a thick seed coat and does not germinate easily. Encourage germination by soaking seeds in water four to six hours or overnight immediately before planting. The seed must be surface-dried for mechanical planting.
Before planting, carry out a soil analysis and follow its recommendations. A high level of nitrogen (N) will cause excessive vegetative growth, reducing yield.
If soil tests indicate a high pH, apply lime three to four months before seeding.
The following are recommendations; adjust, if need be, to suit farm conditions.
Before planting, apply:
- Nitrogen: between 13kg/ha and 22kg/ ha at planting. Side-dress with an additional 16kg to 23kg N/ha when the plants are 20cm to 25cm tall, or use 11kg N/ ha after first fruit set, and again after four to six weeks. Nitrogen is necessary to ensure a long harvest period. Avoid excessive rates, as they can cause the okra to become too vegetative, which will reduce yield.
- Phosphorus: 23kg to 45kg/ha, all applied at, or before, planting. Irrigate every 10 days. Don’t over-water, as this may drown plants or cause excessive growth. When using furrow irrigation during harvest, water alternate rows, and use the dry furrow to walk on during harvest. Apply subsequent irrigation to the dry furrow.
Weed species that threaten okra include annual grasses such as crabgrass and goose grass; perennial grasses such as Bermuda grass; and broadleaf weeds such as sicklepod. When the okra and weeds are small, till with a rolling cultivator to kill off the bulk of the small weeds. Later, use a sweep cultivator or a rolling cultivator set to cover small weeds within the row.
Avoid throwing too much soil directly against the okra stems; this can increase the incidence of stem rot.
A few herbicides are registered for weed control; be sure to use them properly to avoid damaging your crop.
Okra is harvested over a long period, so you will need to control the weeds for the full season.
To control grasses, apply Treflan before planting. There are no herbicides suitable for broadleaf weed control in okra.
Use mechanical cultivation as often as necessary to control broadleaf weeds. Cultivate as shallowly as possible to avoid root damage to the okra. Avoid lands with known heavy infestations of broadleaf weeds.
Damage from insects varies from year to year and differs at each stage of plant development. Aphids usually attack okra early in the season. Later, plants and pods may be attacked by stinkbugs, cabbage loopers and leaf-footed plant bugs.
Chemical control of insect pests of okra can be a problem, as few insecticides are registered for use on this crop. It is best to scout for pests and use biological control.
There are two types of insect pests that target okra: foliage (leaf) feeders and pod feeders.
These can reduce yield, but only when their numbers are high or when the plants are young or stressed. Foliage-feeding on well-established plants doesn’t normally cause yield loss, as healthy plants can lose many leaves before a drop in yield occurs.
Because young plants are more susceptible to foliar feeding damage, scout the plants frequently to check for insects. If you see moderate feeding damage on young plants, you should control the pest.
The following are the primary foliage-feeding insect pests of okra:
- Flea beetles. These tiny, dark, highly active insects cause small, round holes in the leaves (shot holes).
- Blister beetles. These have narrow necks and soft, elongated bodies 0,5cm to 0,75cm long, and feed on both leaves and blossoms.
- Caterpillars. These include loopers, and create holes in the leaves.
- Aphids. These pests damage plants by sucking sap from the foliage.
These insects are a greater problem than foliage feeders because damage to pods or blossoms directly affects the pod, which is the edible part of the plant. Once flowering and pod set begin, check the blossoms and pods regularly for insects and feeding damage.
The following are the main pod-feeding pests:
- Corn earworms. These chew holes and tunnel into pods.
- Stinkbugs and leaf-footed bugs. These suck sap from both the blossom and pod, causing small, dark, raised blister-like spots on the pod. Feeding on very young pods causes them to become distorted.
Ensure that plants have favourable growing conditions, such as enough water and fertiliser, particularly when small. Strong, healthy plants are better able to tolerate insect damage.
Many insects overwinter in debris and weeds. Remove these refuges in autumn after the harvest in order to reduce infestations the following spring.
Practise weed control during the season on and around the land to reduce populations of flea beetle, blister beetle and aphid. Plant early to reduce damage by several caterpillar species, as large populations don’t usually develop until later in the season.
Very few insecticides are registered for okra. Therefore, as noted, practise frequent scouting and cultural controls.
Southern stem blight and Verticillium and Fusarium wilts are some of the more serious diseases of okra. One way of controlling them is to practise crop rotation.
In rainy or wet seasons, blossoms and pods can rot when the plant canopy is dense. Remove the lower leaves to allow better air circulation and reduce this problem.
Blossom blight is caused by the fungus Choanephora cucurbitarum. Blossoms, and sometimes very small pods, are covered with a cottony growth tipped with black fungal fruiting bodies. The pods fail to develop.
The disease is more severe during periods of high humidity, which is often the entire growing season. No effective fungicides are approved for use on okra. The best control is to avoid over-fertilisation and planting in low areas or shady sections of land.
Also, avoid overhead irrigation late in the day. Plants need time to dry off before nightfall.
Leaf spot of okra can be caused by a number of fungal pathogens. However, leaf-spot diseases rarely cause significant damage to okra. The best control is to follow a suitable crop rotation sequence and a balanced fertilisation programme.
Harvesting and handling
Harvest okra pods while they are still tender, which is usually five to six days after flowering. Most customers prefer pods 5cm to 8cm long.
Harvest two to three times a week, as regular picking increases yield. Mature pods left on the plant reduce flowering and fruit set.
Use a knife to cut the pods off the plant, or simply snap them off by hand. If the tip of a pod bends between the fingers without breaking, the pod will be too tough for use as a fresh vegetable.
Okra pods lose moisture rapidly after harvesting, which causes a loss of quality. For this reason, harvest during the cooler parts of the day (early mornings or evenings) and keep the harvested okra as cool as possible.
Store harvested okra in ventilated containers. Pods kept in non-ventilated containers lose their colour rapidly due to bleaching.
Handle harvested okra carefully to avoid bruising. Bruised pods will turn black or brown within a few hours. Cotton gloves are recommended when harvesting and handling pods.
In addition, okra plants and pods have small spines that can cause an allergic reaction. Handlers and pickers should wear long-sleeved shirts as well as gloves for skin protection.