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Cotton
pests (Northern Namibia)
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Gossypium L.
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Cotton
(English)
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? (Oshiwambo)
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1. Cotton Introduction
Cotton growing has been introduced for
small holder farmers in northern Namibia a few years ago, so the pest pattern
is not well known yet. In other countries, Cotton is known for hosting
many pests but the first observations from mainly commercial growers growers
in Oshikoto region indicate that the pest problems may not as serious as
we had expected.
During March-May 2000 a number of
affected cotton bolls were collected from 7 fields in the area. Each sample
consisted of about 10 affected bolls. The bolls were kept in separate cages
with a net over the cages. Eventually a number of moths hatched
from the cages and were pinned. At the same time, Cotton stainers
were collected directly on the plants.
Hatching moths from cotton bolls
is very easy. The affected bolls are picked as fresh and placed in a small
plastic basin on a layer of dry sand. An insect-proof net is placed over
the cage. Caterpillars do not need supplementary feeding as they continue
eating from the bolls. Eventually the moth will hatch and sit on the insect
net, ready to be killed and pinned. At the end of the day all cotton bolls
have dried up and opened and the materials are discarded.
The moths that have been found so
far are quite esay to distinguish from each other at caterpillar stage.
The red caterpillars are red bollworms, the spiny are spiny bollworms and
all the remaining are Amercian bollworms which show a wide variety of coulours.
For fast identification in the field, one should cut up some affected cotton
bolls and have a look at the caterpillars found inside.
Collection and identification of
cotton pests will continue in the 2000/2001 season.
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Sample site
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Region
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Species seen in sample
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Reared & pinned
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| Ondobe |
Ohangwena |
Cotton stainers
Red bollworm |
+
+
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| Outapi |
Omusati |
Red bollworm |
+ (both forms)
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| Omundaungilo Community |
Ohangwena |
American bollworm
Spiny bollworm |
+
+
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| Omundaungilo ARDC |
Ohangwena |
Cotton stainers |
n.a.
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| Epembe |
Ohangwena |
Red bollworm |
+
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| Okankolo 1 (Ondiikalela project) |
Oshikoto |
Spiny bollworm
Red bollworm |
+
-
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| Okankolo 2 |
Oshikoto |
none |
-
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Other observations
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The microlepidoptera, False Codling
Moth (Cryptophlebia sp.) was reared from ripe Guava fruits
(Mahenene Research Station, Omusati region) on 29 April 2000. This species
is reported as common on cotton in other countries and may therefore turn
up in cotton samples as well.
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Aphids or thrips have been reported
as a problem in cotton from other fields in the area. This should be verified
during the coming season, as the names may be used incorrectly.
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For unknown reasons many technicians
refer to the cotton stainer as 'thrips' and also call all bollworms for
'American bollworm' although most of the bollworms found in the bolls were
actually the red and the spiny wollworms.
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With cotton production on the increase,
it is of interest to look at the wild Malvaceae plants in the area.
They may be host plants for pests that affect cotton. Apart from two new
beetles on the flowers of wild stockrose nothing unusual has been found
yet. (No 82 and No. 85, still under identification)
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A few left-over cotton plants were examined
for pests after the winter seson. They still had unopened cotton bolls
but there were only very few holes from bollworms on such plants. It seems
the winter and the dry spell clears up most of the pest problems.
2. Cotton
pests
The following few species have
been found and described until now. More will follow during the beginning
of 2001
3. Insects on other Malvaceae
These species were found on weeds of the Malvaceae. They may therefore
turn up on cotton as well.
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