CropLife South Africa received notifications from livestock and crop farmers in the Gauteng and Mpumalanga provinces on 17 February 2025 regarding the possibility of a large-scale outbreak of the indigenous African armyworm, Spodoptera exempta Walker (Lepidoptera: Noctuidae) in the northeast of Pretoria extending to Lydenburg, Carolina, Bronkhorstspruit, Witbank and Stofberg.
These armyworms are generally blackish (1A) in colour but can be brown to green (1B). Unlike the Fall armyworm, the African armyworm lacks the clear spots and from images received, it is clear that this is the black, crowded or gregarious form (1C) – clearly identified by the black head.
They are usually found in masses on grasses and do not hide in crops during daytime like the Fall armyworm. In the swarming phase, the species can be particularly damaging to cultivated grazing fields and natural veld, but seldom has an economic impact on perennial and cash crops.
Sporadic African armyworm outbreaks in the country are not uncommon and mostly occur in the grassland biome which covers the North West, Gauteng, Mpumalanga, Free State and KwaZulu-Natal provinces, as well as parts of Limpopo. Outbreaks, based on records to date, generally follow the onset of wet seasons when dry grasslands produce new growth and cereal crops are planted. Major outbreaks of armyworms are commonly preceded by extended drought.
All farmers are advised to be on alert and should African armyworms be identified, to inform CropLife SA about the occurrence by sending good quality images with location details via WhatsApp to Dr Gerhard Verdoorn on 082 446 8946 or Hiresh Ramanand on 082 497 6975. CropLife SA will escalate the information gathered to the Department of Agriculture, Land Reform and Rural Development (DALRRD): Plant Health Directorate.
There are registered pyrethroid insecticides that may be applied to control African armyworm outbreaks in veld, grazing and various crops. According to the scientific literature, for insecticides to be effective, the African armyworms must be found in time. Chemical control is documented to be effective if applied as soon as the African armyworms have emerged (1-5mm long). With that said, it remains imperative that all farmers adhere to the product label directed instructions without deviation. Farmers are reminded that a pesticide product label is a legal document covered under the Fertilizers, Farm Feeds, Agricultural Remedies and Stock Remedies Act, 1947 (Act No. 36 of 1947).
CropLife SA would like to alert all farmers to the presence of millions of migratory birds that will feed on the armyworms, hence, to be particularly cautious when deciding whether to control the outbreak or leave it to nature to take its course. The association does not believe at this stage that the outbreak in natural veld warrants any control because the excellent rainfall has brought very good basal ground cover that will recover rapidly in the event of damage.
Where broad bands of African armyworms are found on farm roads and tracks, these can be destroyed by pulling heavy sails over them behind a vehicle. African armyworms moving from one land to another, can be halted by ploughing a furrow with “pits” dug at intervals. The armyworms will crawl along the furrows and eventually fall into the pits where they can be covered up.
One aspect of African armyworm outbreaks is the poisoning that sometimes follows an 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 armyworms, and only some kikuyu pastures produce this toxicity.
Symptoms in cattle are as follows: the swallowing of affected cattle is paralysed, appearance of large ‘strings’ of watery saliva drooling from the mouth, and the cattle exhibit an apparent severe thirst. Slight symptoms of bloating, grinding of teeth, and nervous twitching may occur. As soon as symptoms are observed, all cattle should be removed from the affected pastures and a vet should be called in. A good general prevention measure to avoid further poisoning is the removal of all animals from the pasture for a period of at least 40 days.
Finally, it is important for farmers to note that, should the caterpillars be discovered when fully grown, the use of insecticides is often not recommended since most of the damage to crops and grazing veld will already have occurred, and the emerging adults would likely move off and not produce a second generation in the same place. However, with that said, farmers are urged to be vigilant. Therefore, early morning scouting now becomes imperative during this period in deciding whether to apply an insecticide or not.
