PEST AND DISEASES OF OKRA
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The diseases of Okra include:
- Damping-off: Seedlings appear wilted, yellowed and either depression, light brown ring-shaped lesions or water-soaked, dark green lesions are found on the collar. This disease can cause an 80% reduction in okra seed emergence. The very widespread disease mostly affects seed germination (pre-emergence damping off). When damping-off occurs, seedlings emerge later and are sparse.
- Fusarium wilt: In the event of a severe attack, many leaves droop and become chlorotic. This produces overall wilting of the plant which subsequently dries out and dies. Infections are most likely to occur in soils with low potassium content and high acidity.
- Cercospora leaf spots / Cercospora leaf blight / Black mould: The disease weakens the plant’s assimilation capacity by diminishing the leaf area which adversely affects fruit yield. The disease shows on the lower surface of the leaves as greyish spores that later become black and sooty.
- Powdery mildew of okra: On the leaves, the disease shows on both surfaces in the form of small greyish-white downy spots.
- Bacterial blight of okra: It causes the death of seedlings and loss of young plants and several infections often cause premature leaf fall.
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Viruses
Several species of the virus are liable to infect okra entailing varying degrees of economic impact.
- Okra leaf curl virus: When severe infection occurs at an early stage, the plant’s entire development is affected and growth is retarded or stopped.
- Cucumber Mosaic virus: The leaves and fruit of affected plants tend to develop necrotic areas. Plants that are infected at an early stage remain stunted. Losses are often huge (60 to 90 %) when early infection occurs.
- Cotton Yellow Mosaic Virus: This disease causes stunting, leaf chlorosis and depreciation of fruit quality. When infection occurs at an early stage, the plants remain stunted.
- Hibiscus Yellow Vein Mosaic Virus: This disease is mainly transmitted by an insect vector. Seedlings and plants at the vegetative growth stage, flowering stage and fruiting stage are susceptible to this attack.
Insects
- Okra green stink bug: Stink bugs at different stages of development feed on the sap of host plants. Stink bugs attack okra at all stages of development with a predilection for the floral buds and fruiting stages.
- Cutworms: Young caterpillars, which are yellowish-green with a blackish head feed on leaves while older ones feed on plant stems. The seedling stage is the period of highest susceptibility.
- Cotton aphid: Aphids attack okra at all stages of development, with a predilection for the juvenile stages. These aphids have a symbiotic relationship with ants. Ants provide protection to aphids from their predators, while feeding on the honeydew produced by the aphid.
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- Tobacco whitefly: Direct damage is caused by poison injected by tobacco whitefly feeding, giving rise to chlorotic areas on the leaves and sprouts of Okra plants. Okra is attacked by whiteflies at all stages of development with a predilection for the juvenile.
- Cricket: Cricket feeds on juvenile shoots and leaves and hence tends to devour the terminal buds of seedlings and cut their stalks off.
- Cotton semi-looper: The larvae of cotton semi-looper feed on leaves, making holes, and sometimes attacked leaves are ripped up, leaving only the midrib and veins. The insect eats all the intermediate tissue mainly on the upper, juvenile leaves.
- Cotton strainers: When the insect attacks juvenile fruit, they tend to dry out and end up dropping off. Pods attacked when near maturity stage develop spots at the numerous toxic bite wound locations and dry out.
- Spiny bollworms: The caterpillars feed on the content of floral buds, flowers and pods of okra plants. These organs are sometimes visibly perforated. On the pods, caterpillars dig entry points that are subsequently invaded by saprophytic fungi.
- Thrips: Thrips feed on the lower surface of the leaves, on flowers and fruits. Damage results from both larvae and adults puncturing the plant tissue and sucking the exuding sap. Attacked plant parts frequently have a silvery sheen and show small dark spots of faecal material.
- Mole-cricket: Mole-crickets disrupt seedbeds by digging holes and tunnels. Hence seeds either fail to germinate subsequent to attacks or else are moved thereby disrupting crop alignment.
- Cotton bollworm, African bollworm: Bollworm caterpillars attack floral buds, flowers and pods. They make large holes in the leaves, eat into floral buds and perforate pods producing cavities of various sizes.
- Leafhopper or jassid: Symptoms begin as yellowing of leaves, then the edges become brown or red and discolouring extends to the interior area of the leaves.
- Lagriid beetle: Holes of variable size appear on the lamina as a result of the insect feeding on the foliar tissue. The economic impact of Lyillosa is minor because it is not voracious and is rarely abundant on okra except in the rainy season. Additionally, the impact of attacks is offset by the production of new leaves.
- Leafminers: Leaves that have been attacked by larvae become necrotic when the larvae emerge and large portions turn brown thereby reducing photosynthetic activity.
- Blister beetles, flower beetles: Symptoms are visible on the leaves in the form of holes on the lamina. On floral organs, the petals, stamen and pistil are all devoured which gives rise to varying degrees of seed abortion. As a result, losses may be extensive depending on the severity of pest infestation.
- Cottonseed bug: Symptoms are visible in seed production, fields on fruit whose seeds attacked during the ripening process. The seeds are often wrinkled and have tiny brown or blackish dots, which are the insect bite wounds. These bites diminish the germination capacity of the damaged seeds.
- Cetonia: Adult insects attack leaves and stalks as well as young okra pods. Damage to leaves and stalks causes abnormal growth of the plant and deformities.
- Flea beetle: Young seedlings are the most vulnerable to flea beetle attack. Heavy insect attacks at the initial stages of the growing season can seriously jeopardise okra yield entailing losses of 30 to 70 percentage.
- Mealybug: The leaves located beneath the mealybugs colonies are covered with sooty mould thereby diminishing photosynthetic activity. Severe attacks interfere with plant growth and lead to a substantial decrease in yield.
- Armyworm: Damage caused by armyworm attack can be very extensive depending on the size of larval populations.
- Leaf roller: Pieces of okra leaves are cut out and rolled by the leaf rollers. In many cases, when many leaves are affected, the leaf area and hence photosynthetic activity are diminished. In the event of heavy attacks, plant growth may be hindered.
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- Okra white grubs: Visible symptoms range from wilting to the lodging of affected plants. When extremely high larval density occurs at the beginning of the rainy season in a very humus-rich, moist soil, considerable losses may be generated.
- Cotton worm: The caterpillars are phyllophagous and symptoms are visible on leaves, which are devoured or from which large pieces have been cut out. Damage is generally minor as this pest is not usually very abundant in okra field.
- Variegated cricket: Adults feed on the entire leaf leading to defoliation of the plants. Additionally, when massive infestations occur, the entire plant may be devoured right down to the root at the soil line level.
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