SA Grain May 2017

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Mei 2017
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The invasion of the
fall armyworm in South Africa
Since the first fall armyworm larvae were collected in the
Settlers area mid-January this year and reared through to
moths for identification, Dr Vivienne Uys (ARC-PPRI) made
the positive identification in early February as Spodoptera
frugiperda (JE Smith) (Lepidoptera: Noctuidae).
From there on the requests for identification from producers have
increased and soon this pest was reported in Limpopo, Mpuma-
langa, North West Province and Free State (Figure 1). This pest
has struck us like lightning and now we have more questions
than answers.
The fall armyworm has invaded South Africa in January, after re-
ports of invasion in West and Central Africa. This species mainly
established in maize fields in South Africa. Other crops that were at-
tacked in South Africa were sorghum, sweet corn and potatoes. The
first observation of fall armyworm on the Africa continent was made
in late January last year on maize in the rainforest zone of South-
Western Nigeria and in maize fields at the International Institute of
Tropical Agriculture (IITA) at Ibadan and Ikenne.
Later that season high numbers of fall armyworm were also reported
from northern Nigeria, Benin and Togo. In April last year government
of São Tomé and Principe called for assistance from the Food and
Agriculture Organisation of the United Nations (FAO). Thereafter, in
June last year, the Federal Government of Nigeria reported fall army-
worm on maize in Edo and adjacent states in the southwest of the
country. This pest then spread through the rest of Africa, travelling
southwards to South Africa in a little bit more than nine months.
Description and life history
The life cycle of the fall armyworm is about 24 to 30 days in favour-
able temperature and humidity. The number of generations occur-
ring in an area will vary with the appearance of the dispersing moths.
This species does not have a diapause (overwintering) stage.
Eggs
The eggs are dome-shaped with a flat base and curves upward to a
broadly round point. Eggs are lain in egg batches attached to foliage.
Egg batches vary, but can be 100 to 200 eggs.
A female moth can lay more than a 1 000 eggs. The female deposits
a layer of greyish scales over the egg batch, which appear furry. The
duration of the egg stage is two to three days depending on favour-
able conditions (Photo 1a and Photo 1b ).
Larva
Newly hatched larvae are green. Colour change as larvae mature.
Larvae are smooth-skinned and vary in colour from light tan or green
to nearly black. Three yellow-white lines run down the larval backs.
On each side of the larval body, next to the yellow lines, is a wider
dark stripe.
To differentiate the fall armyworm from other species a predomi-
nant white, inverted Y shape is present on the forehead between
the eyes (Photo 2). The duration of the larval stage can be as short
as 14 days in summer. Unlike other armyworms, larvae feed during
the day and night.
Pupa
Pupation normally takes place in the soil, but can also, if soil is too
hard, take place by webbing together leaf debris. In the soil larvae
construct a cocoon with soil particles with silk to pupate in. The du-
ration of the pupal stage is about eight to ten days during the sum-
mer.
Adult
The moths are strong flyers and have a wingspan of 32 mm to
40 mm. Moths are active during the night. The forewings of the male
moth are shades of grey and brown, with triangular white spots at
the tip and near the centre of the wing. The female forewings are
less distinctly marked. The hind wings are silver-white in both sexes.
Duration of the adult stage is about ten days.
Larvae should not be mistaken for the African armyworm
(Photo 3), the lesser armyworm (Photo 4), the cotton leaf worm
(Photo 5), the African bollworm (Photo 6), the false armyworm
(Photo 7) or the common cutworm (Photo 8).
Different strains
Fall armyworm consists of two genetically differentiated strains
commonly referred to as the rice-strain (R) and the maize-strain (M).
The R-strain is known to attack rice, pasture, turf grass, Bermuda
grass, millet and alfalfa, whereas the M-strain attacks maize, sor-
ghum and cotton.
The two strains also have different timing for mating activities. Fe-
male calling and mating occur early in the night for the M-strain and
during the last half of the night for the R-strain.
Host plants
Fall armyworm is polyphagous which can attack maize, sorghum,
Bermuda grass, soybean, cotton and beans. It is reported that fall
armyworm larvae can attack over 60 species of plants representing
more than 20 families.
However, it has a definite preference for graminaceous hosts and
will probably confine its attack to these crops if continually available.
Because of its wide host range, this specie is one of the most harmful
pests threatening annual crops in tropical regions.
Damage
Larvae cause serious leaf feeding damage as well as direct injury
to the tassel and ears. Larvae can cause damage to nearly all maize
stages of development, but will concentrate on maize plants that
have not yet silked.
The most common damage is to late pre-tassel maize. Maize plants
often recover from whorl damage without reduction in yield. With
tasselling larvae may partly or totally destroy young ears, which
is more important than leave damage. Usually damage is found in
patches in the field.
Management
Fall armyworm can be one of the most difficult insect pests to con-
trol in maize. Fall armyworm can only be effectively controlled while
the larvae are small.
ON FARM LEVEL Fall armyworm / Different strains / Management Integrated pest control
DR ANNEMIE ERASMUS, ARC-Grain Crops , Pothefstroom