The City of Tshwane would like to advise farmers in Tshwane about the current African armyworm outbreak. The worm was first discovered in the week of 10 February 2025 on farms along the N4 in Region 7 of Tshwane, and it has since spread from the surrounding areas to the other regions of Tshwane.
This pest affects or feeds on pastures (grass) and cereal crops. The first report was from a 30 ha Smutsfinger grass field, and the armyworm has been spreading to other grass cultivars, including cereal crops. It has a more serious effect on cereal crops that are still at an early vegetative growth stage.
Livestock farmers are advised to be vigilant, as some grass, such as Kikuyu grass, release a chemical when it is attacked by the worm that makes the grass toxic to cattle. This may cause sickness among livestock.
The worms are carried by the wind and invade the area as moths, which lay eggs and breed. The lifespan of the African armyworm from egg to adult moth is between one to three months. They are very susceptible to cold conditions. It is believed that the infestation will reduce as the winter season approaches.
The caterpillars develop from grey-green with white-yellow stripes at the back when they are small to black with thin blue lines down the middle of the back and yellow-green lines outside the blue lines when they are fully grown. They measure 2 cm to 3 cm long when fully grown.
There are registered pesticides (insecticides) to control this pest, most of which have mercaptothion (organophosphate) 500 g/ℓ as an active ingredient. Farmers are advised to use registered pesticides and to follow the application label correctly, taking care to wear protective clothing. Armyworms can become resistant to insecticides if the same type of product is used repeatedly. Overuse of selective insecticides can increase the resistance levels in armyworms. Other control methods for armyworms include ploughing furrows with pits dug at intervals to stop the caterpillars from moving from one field to another, as well as covering up or treating the larvae that fall into the pits with chemicals.
The City of Tshwane appreciates the support of the Gauteng Department of Agriculture and Rural Development, which is distributing pesticides to the affected farms.
For further enquiries, please contact Egnes Shiba on 012 358 4109 or egness@tshwane.gov.za.