Plantwise Factsheets for Farmers
Aphids on Brassica
Recognize the problem
Cabbage aphids are green to pale grey insects with a white, waxy coating. They are soft-bodied insects found in groups, often underneath the leaves. They cause misshapen leaves, spread virus diseases and produce a sugary substance called honeydew. This substance 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 cabbage heads and leaves.
Aphids grow into adults after a few days and get into groups usually on the underside of leaves and young foliage. Aphids can also live on other plants or weeds. If not controlled, aphid populations can become very large and spread in the field. Natural enemies such as ladybird beetles, lacewings and hoverflies kill the aphids. Aphids do not like the strong smell of some plants. They are easily washed off by soapy water.
- 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, syrphid fly larvae and parasitic wasps. Supply flowering plants for the adult syrphids to feed on and avoid spraying pesticides when there are enough natural enemies in the field to reduce the number of aphids.
- 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.
- Spray with a biopesticide such as Beauveria bassiana.
- Effective chemical products to use include Azadirachtin (neem), Bifenthrin, Deltamethrin, Pirimicarb, Pymetrozine and Lambda-cyhalothrin.
When using a pesticide, always wear protective clothing and follow the instructions on the product label, such as dosage, timing of application, and pre-harvest interval.
The recommendations in this factsheet are relevant to many countries where this pest or problem is present
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