Armyworm reported at Nkandla
Farmers who discovered the worms have been advised to remove their cattle from affected pastures
AN outbreak of the African Armyworm (Spodoptera exempta) has been reported in the Msinga and Nkandla districts by the Department of Agriculture and Land Reform.
This must not be confused with the Fall Armyworm (Spodoptera frugiperda), although both species belong to the same order of Lepidoptera.
Farmers who discovered the worms last week, have been advised to remove their cattle from affected pastures.
For control measures to be effective, it is important that the worms are discovered early in their life cycle.
If 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 location.
Another factor playing a role is temperature, as the caterpillars require temperatures of between 24-32 degrees centigrade to develop.
Anything below this will hinder development and often cause death of the larvae.
Furrows
Where the caterpillars move 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 chemicals.
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).
Affected cattle are paralysed with the appearance of large ‘strings’ of watery saliva drooling from the mouth.
Animals also exhibit severe thirst.
Slight symptoms of bloating, grinding of teeth and nervous twitching may occur.
The removal of all animals from the pasture for a period of at least 40 days is recommended.
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