Brassica aphids are green gray insect pests with a white waxy coating, which commonly occur in dense colonies, often covered with waxy droplets.
They cause misshapen leaves, spread virus diseases and produce a sugary substance called honeydew, which sticks on the leaves and encourages a black fungal growth. The feeding of the aphids causes leaves to curl around the pests, making them harder to reach with pesticide applications and producing unmarketable produce.
These aphids feed on many varieties of produce, including cabbage, broccoli, Brussels sprouts, cauliflower and many other members of the genus Brassica.
Drought stressed crops are at greatest risk as aphid colonies increase rapidly on such crops.
If not controlled, aphid populations can become very large and spread in the field within no time causing significant damages.
LIFE CYCLE
- brassica has a simple life cycle with adult females giving birth to live offspring throughout the year, parthenogenetically. It overwinters as black eggs in host plant debris near the soil surface.
These aphids have a rapid development time, usually 8-12 days from first-instar nymph to adult, and get into groups usually on the underside of leaves and young foliage. They can also live on other plants or weeds.
They complete up to 15 generations, often overlapping during the growing season.
FEEDING & DAMAGE
Brassica aphids cause direct damage to the crop by sucking its sap and indirect damage through transmission of viruses which affect crop performance.
Feeding damage from large numbers of aphids can kill seedlings and young transplants.
On larger plants, feeding damage results in curling and yellowing of leaves, stunting plant growth, and deformation of developing heads.
Dense populations of these aphids cause leaves to curl around them, making them harder to reach with pesticide applications.
Contamination by dead aphids can be a problem, as they do not wash off easily and thus cause the produce to be unsuitable for fresh market sales.
Symptoms of viruses transmitted by B. brassicae include mosaic, chlorotic and necrotic lesions on leaves, premature leaf senescence and various degrees of stunting, leaf rolling and leaf distortion.
While feeding, they also secrete honeydew that facilitates the development of sooty mold, which reduces the photosynthetic surface of the crop and greatly reduces its value.
MANAGEMENT STRATEGY
Chemical control
The following are effective chemical products/insecticides to use in control of brassica aphids, which have both contact and systemic properties;
- AMAZING TOP 100WDG 5g/20l
- EMERALD 200SL 10ml/20l
- EMERALD GOLD 700WDG 5g/20l
- EPITOME ELITE 500SP 10g/20l
- KINGCODE ELITE 50EC 10ml/20l
- PENTAGON 50EC 10ml/20l
- LEXUS 247SC 8ml/20l
- BACIGUARD 16WDG 15g/20l
- LOYALTY 700WDG 5g/20l
- PRESENTO 200SP 5g/20l
- PROFILE 440EC 30ml/20l
- SINOPHATE 750SP 20g/20l
- TAURUS 500SP 10g/20l
Non-chemical control
- Remove and destroy crop remnants/residues immediately after harvest.
- Remove other hosts such as related Brassica or other cruciferous weeds from around field borders.
- Conserve natural enemies such as lady beetles and parasitic wasps.
- Grow strong smelling repellent plants like onions and garlic near the crop.
- Remove and destroy infested plants from the field.
- Apply nitrogenous fertilizers moderately because too much of it will make the plant soft and juicy making it attractive to aphids
- Use yellow coloured traps to attract and kill adult aphids.
- Practise rotations with non-host crops
- Plant resistant varieties
- Maintain field hygiene/sanitation
- Ensure proper weed control
Note;
- Mix insecticides with INTEGRA 3ml/20l whenever spraying. This is a sticker, spreader, and penetrant which enhances the effectiveness of the chemical.
- JAMBO CLEAN 100ml/20l is used to clear the sooty mold.
- Timely control of the pests is very crucial
- When using a pesticide, always wear protective clothing and follow the instructions on the product label, such as dosage, the timing of application, and pre-harvest interval.
- Although aphids can be easily controlled using insecticides, it is advisable to alternate various chemicals within a crop season. This prevents resistance build up by the pest against either of the insecticides.
