| Cabbage
aphid |
Namibian
crop pests # 70
|
| Brevicoryne brassicae (L.). |
Order: Homoptera
|
Family: Aphididae
|
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Note:
This page is brought to you courtesy of Menno Keizer and Jantien
Zuurbier, who worked at the Kavango Horticultural Production and Marketing
Project. For further information please email them directly at: mennojantien@yahoo.co.uk
Colony of aphids on cabbage
|
Aphid colony
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Common names:
|
Cabbage aphid (English),
Ghushi
(Gciriku), Plantluise (Afrikaans) Omudjenene (Oshikwanyama),
Oshizenene
(Oshimbalantu),
Oshikagadhi (Oshindonga) Omule (Oshingandjera,
Oshikolonkadhi, Oshikwaluudhi) |
Host:
|
The main host plant is cabbage,
but they can be found on other members of the Cruciferae. |
Pest status:
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Aphids are a major pest of cabbage
and cauliflower in most areas where they are grown. Attacks are particularly
severe in dry seasons following good rains. Radish, kale and most other
Brassicas are attacked but less severely than cabbage; turnips appear to
be immune.
Aphids are an important vector of
many virus infections. |
Description:
|
Adults may be wingless or winged
and are of medium size (1.6 mm – 2.8 mm). They are always covered with
a fine grey, mealy, powdery wax, which covers the basic greyish-green to
dull mid-green colour of the aphid. Only females are found and living young
are produced. Cabbage aphids are usually found in colonies feeding
on the underside of leaves.
The optimum temperature for development
is 20°C, survival rate is decreasing when temperatures are rising above
30°C. |
Damage:
|
Masses of soft, mealy-grey aphids
are found feeding in clusters on leaves sucking the sap from the plant.
Infested seedlings may be stunted and distorted. White cast skins and drops
of sticky honeydew and/or sooty mould growing on the honeydew can be seen
on the leaves. Down-wards curling of the leaves occurs. All these symptoms
affect the marketability of the cabbage heads considerable. |
Control:
|
Biological control:
In Namibia no collection or identification
has taken place to identify natural enemies of the cabbage aphid, although
larvae and beetles of the ladybird have been seen feeding on the aphids
in gardens in the Kavango Region.
In other countries natural enemies
have been studied in great detail. Aphids are naturally controlled by parasitic
wasps of the family Aphidiidae and Aphelinidae, predators (ladybird beetles
and hover flies) and pathogens. The sweet honeydew often attracts ants.
Ants are living in companion with the aphids; occasionally protecting them
from predators.
Use of botanical pesticides:
Most aphids can be controlled on smallholders’
plots by washing the aphids of with lots of water. This species however
is more difficult to kill as its body surface is covered with a fine wax,
which is water repellent. Soap can be added to the water as an additional
“wetter”. Also cattle urine, left overnight in a bottle to ferment and
diluted with water, has shown good results in aphid control.
Farmers in the Kavango region are
using ash diluted in water and sprinkle this on the plants. It is believed
that the alkalinity of the ash extracts fluids from the aphids and cause
them to dry out.
Cultural practices:
At present no resistant varieties are
available, however glossy green-leafed cabbage lines with a low wax layer
tend to be less susceptible.
Chemical control:
Contact or systemic insecticides may
be used in case of severe attacks. Spray applications should be directed
to the underneath of the leaves where most aphids are usually to be found. |
References:
|
Keizer, M., J., Zuurbier, Manual
of Integrated Pest Management Course for Extension staff, Mashare Agricultural
Development Institute, Rundu, Namibia, April 1999.
Varela, A.M., A.A., Seif, Crop protection
manual for Brassicas, ICIPE, Nairobi, Kenya, June 1999. |
Other pages by the same authors:
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