What are whiteflies?
Whiteflies are insects that cause direct damage to plants by sucking plant sap and removing plant nutrients, thereby weakening the plant. The adult has two pairs of wings that are held roof-like with a pale yellow body.
They are mostly white but can also be yellowish, with some species having dark or moulted wings. They are primarily clustered in groups on the underside of young leaves and readily fly away when disturbed.
The adult females lay eggs that are white but may gradually turn brown. Depending on species and humidity, they hatch after 5-10 days into the crawler (immature stage) at 30degC. This explains the higher population in the greenhouse than outdoors.
The crawler is mobile. It moves to a suitable feeding location, where it moults, loosening the legs and antennae. It later passes to the nymph stage. Nymphs are usually oval or oval elongated in shape and simple in appearance, like small-scale insects. Nymphs later mature into adults.
Even though whiteflies don’t fly very efficiently, once airborne, they can be transported by the wind for long distances. This explains why controlling whiteflies on outdoor farms doesn’t seem very easy.
Host crops
Tomato, cabbage/kale, brassicas, cassava, citrus plants, cotton, cucumber, eggplant, green gram, mango, sweet potatoes, melons, peppers and pumpkin
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Damage caused
Whiteflies produce a large quantity of honeydew, which leads to the growth of sooty mould on the lower leaves, blocking or reducing plants’ photosynthetic capacity.
Honeydew also contaminates the marketable part of the plant, reducing its market value or making it outright unsaleable. When whitefly infestation is severe or of long duration, infected plants may wilt, turn yellow in colour, become stunted, or die. Whitefly is a vector of tomato yellow leaf curl virus, a critical virus disease in tomato farming.
How to identify whiteflies
Whiteflies are recognized by a cloud of tiny whiteflies flying up when the plants are shaken. They resettle soon on the plants and affect plants at the seedling, vegetative, and flowering stages.
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Pest management
- Ensure adequate growing conditions for the crop, such as good soils, adequate water supply, proper feeding (avoid applying high doses of nitrog fertilizers since they favour the development of the pest), correct spacing, and good nursery management to start the crops with healthy, vigorous plants.
- For early detection, inspect for adults and eggs at the seedling stage found on young leaves. Watch out also for whiteflies flying up when the crop is disturbed.
- Yellow sticky traps are used to monitor the presence of whiteflies for the timing of interventions.
- Intercropping tomatoes with capsicum or cucumber has reduced the number of whiteflies compared to tomatoes alone or tomatoes planted with eggplant alone. Planting border rows with coriander and fenugreek will serve as windbreaks and repel whiteflies.
- Plant tomatoes resistant to tomato yellow leaf curl virus TYLC to reduce the effect caused by whiteflies.
- Spraying thunder, belt, or Oberon speed once per week in a nursery in the first month of transplanting and later once every two weeks will help destroy the crawlers, nymphs, and adult whiteflies. If the whitefly population is high, spraying the above insecticides twice a week in double concentration can help.
Reference: Infornet biovision.
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