It is important to know that for control measures to be effective, the worms must be found in time!
the caterpillars are discovered when they are fully grown, the use of
insecticide control is often not recommended as most of the damage to
crops will already have been done, and the emerging adults will probably
move off and not produce a second generation in the same place.
Another factor that plays a role in South Africa is temperature.
The caterpillar requires temperatures of between 24-32 degrees
Centigrade to develop, and therefore anything below this will hinder
development and often cause death of the larvae.
the caterpillars are moving from one land to another, they can be
halted by ploughing a furrow with "pits" dug at intervals. The larvae
will crawl along the furrows and eventually fall into the pits where
they can be covered up or treated with chemical.
Chemical control is most effective if applied as soon as the worms have
emerged (1-5mm long), as these instars are more susceptible to poisons
than older instars. Two of the insecticides registered in South Africa
for use against armyworm are: cypermethrin and decis (synthetic pyrethroids).
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One aspect of armyworm outbreaks is the poisoning which sometimes follows and infestation. This has been recorded on Kikuyu grass and only affects cattle under field conditions. Symptoms in cattle usually appear about 10 days after the appearance of the worms, and only some kikuyu pastures produce this toxicity.
Symptoms in cattle: The swallowing of affected cattle is paralysed, appearance of large 'strings' of watery saliva drooling from the mouth, and animals exhibit an apparent severe thirst. Slight symptoms of bloat, grinding of teeth, and nervour twitching may occur.
As soon as symptoms are observed, ALL animals should be removed from the affected pastures and a Vet called in. A good prevention of further poisoning is the removal of all animals from the pasture for a period of at least 40 days.