Plantwise Factsheets for Farmers
Ladybirds to control aphids in cotton
Recognize the problem
(Butonje in Tonga) is often attacked by aphids (njina in Tonga, inda in
Nyanja). The aphids are tiny greenish or blackish, soft insects that can have
wing or no wings. They are so small so that you can only just see them. They
often sit in groups on the underside of cotton leaves (= aphid colonies).
There they suck sap out of the leaves. Leaves curl and later become yellow.
farmers see aphids, they start spraying, often every two weeks, which means
that pest scouting (kulangalanga tuuka in Tonga) is not done. However, cotton
plants can tolerate low levels of aphids and there are many natural enemies
that can control these aphids, such as lacewing larvae or ladybird beetles or
their larvae. However, these are killed by the by insecticide sprays which
then causes the aphids to become an even bigger problem because they can
multiply quickly. 1 aphid can produce up to 10 young per day.
beetles are usually orange or red with black or light coloured spots on the
wing covers but the colour can vary and some can be even black. Ladybird
beetles are roundish, hard covered and shiny. Its larvae are black with
yellow spots and 6 clearly seen legs. Ladybird larvae can feed on 50 adult
aphids in 2 days, thus about 500 aphids in 3 to 4 weeks. Ladybirds also eat
aphid eggs. Ladybird beetles are farmer friends that can control aphid
population without the use of chemicals which will help reduce the cost of
Scout for aphid colonies
as well as ladybird beetles and larvae by walking across the field and
checking 10 to 20 plants at a distance of 5 paces between plants. Do this in
at least 3 areas of your field.
- Check the lower leaf, then
the middle leaf and the top of the plant. Ladybirds are often near aphid
- Record the numbers of
aphid colonies if possible, and/or the number of ladybird beetles and larvae
you find 1 ladybird beetle or larvae every 2nd or 3rd
aphid colony (this means per about 50 to 100 aphids), usually no chemical
spray is needed.
- Continue scouting every 1
to 2 weeks to check on aphids and ladybirds.
aphid populations still increase enormously, only then should chemical sprays
The recommendations in this factsheet are relevant to:
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