The outbreak of African Armyworm, a mystery worm which covers large areas of grass, pasture or very small maize and sorghum in dense swarms of worms, has recently been reported in the areas of Ngaka Modiri Molema and Dr Ruth Segomotsi Mompati Districts. According to the crop scientists in the Department of Agriculture and Rural Development, cattle, sheep and goats that have fed on grass that armyworms have been eating, can be poisoned.
Symptoms in affected animals usually appear about 10 days after the appearance of the worms. The symptoms include amongst others, the swallowing of affected animals which becomes paralysed, appearance of large strings of watery saliva drooling from the mouth, and animals exhibit severe thirst. Slight symptoms of bloat, grinding of teeth and nervous twitching may also occur.
Livestock owners are urged to remove animals from the affected pastures when these symptoms are observed, and must urgently inform the local Animal Health Technician or State Veterinarian.
“A good prevention of further poisoning is the removal of all animals from the pasture where armyworms were reported, for a period of at least 40 days”, said the Department’s Crop Scientist, Mr William Weeks, adding that livestock farmers should however be warned about the possibility of secondary poisoning when livestock are allowed back onto pastures too soon after the worms have been sprayed with insecticides. Each insecticide has a specified withdrawal period that should be adhered to, to prevent loss or injury to livestock.
Due to their sporadic population outbreaks which is about once or twice in every 10 years, Armyworms are not government regulated pests. There were outbreaks in South Africa in 1993, 2003, and now again in 2013. These outbreaks were in the past always as a result of large outbreaks initiating in Tanzania and Zambia.
As stated by the Crop Scientist, the climate in South Africa is too cold from April onwards for the moths to survive, hence no new emergence in the next summer season is expected.
The control of Armyworms is done exclusively by the affected farmer. Any insecticide application will kill the worms, and the dose rates are low, but the areas of infestation in the veld can be huge. In the past, hundreds of hectares of grassland were eaten down to the ground by these worms. A dose rate of about 6g a.i./ha Decis (Deltamethrin), 250 ml of 2.5EC Decis per 100 litres of water per ha, and 30g a.i./ha cypermethrin (150 ml of 20 EC formulation per 100 litres of water) will be enough to kill armyworm.
“Apply when worms are visible and moving in the morning. Avoid spraying when too hot”, advised Weeks.
Farmers who have experienced or observed any outbreak of this pest, are urged to inform the nearest Department of Agriculture and Rural Development offices or e-mail to the Information Core for Southern African Migrant Pests (ICOSAMP) Coordinator, Ms. Margaret Kieser at KieserM@arc.agric.za stating clearly the locality of infestation (district, farm name), stage of larvae (green or black), size of infestation (number of hectares), crop infested and full names and a contact number.