COMMON NAMESokalombo (Oshikwanyama, Oshimbalantu, Oshingandjera, Oshikwaludhi, Oshikolonkadi); Kommandowurm (Afrikaans)PEST STATUSThis is a very destructive pest. Always take samples and report any attack.In most years African armyworm is only a minor pest in Namibia. Under favourable conditions, major outbreaks may destroy entire crops on thousands of hectares in a matter of weeks. The most serious damage occur on pearl millet, sorghum, maize and grasses. The speed and intensity of an armyworm attack is unusual because the first stages are rarely reported. Within few days all plants in field may be covered with black caterpillars, several feeding on each. Soon after, the cereals are destroyed and only the inter-cropped cowpea plants are left in the field. DESCRIPTIONThe white eggs are laid in clusters on the leaves. Depending on the temperature they hatch in 2-5 days. The early stages (small caterpillars) are green and often inconspicuous.Armyworm caterpillars are most dangerous in the gregarious form when they gather together and are found in large numbers on plants. In this form caterpillars are up to 30 mm long and have dark stripes that make them appear black. The caterpillar's head is black with a white V-shaped mark. The more common form of armyworm (solitary form) is pale green, but is rarely recognised in Namibia. Because the gregarious forms of the caterpillar often move from plant to plant in large groups they are commonly called armyworms. The caterpillars eat for 10-14 days and then burrow into the ground to pupate. The pupa is brown and covered by a capsule of soil particles (a soil cell) to protect them against drying out. The adult moth has a wingspan of 28 mm. The front wings are dark brown to black with black markings. The hind wings are pure white with a dark edge. CONTROLThe caterpillars are mainly found from January to early March, during which a large outbreak can have severe consequences for young crops. Detection and possible control should therefore begin immediately.Farmers and extension staff have observed that outbreaks of armyworm may be interrupted heavy rain. After a heavy shower, thousands of caterpillars have been found lying dead or dying on the ground, and the attack in that particular field was over. If rain is expected soon, farmers should wait with other control methods, until the effect of rain on the caterpillars can be seen before using other control methods. There is very little known about control methods used by communal farmers, but is has been reported from Ohangwena region that farmers cut branches from trees and “brush” the caterpillars off the pearl millet plants Chemical control is made difficult as many fields in north central Namibia are small and surrounded by open water during the rainy season (“oshanas“ and ponds) which is used for fishing and watering livestock. If chemicals are used, it is important to select chemicals that are not toxic for fish and animals. Contaminating water resources must be avoided by all means. If chemical control is found necessary, please contact the FSRE pest officers for precise advice on chemical control. The contact numbers and addresses are listed on the cover. PREDATORSFarmers, especially from Omusati region, have reported that caterpillars of African armyworm were eaten by cattle egrets (Egretta egretta), i.e. the white birds that follow livestock.OTHER NOTESPheromone traps have been distributed in northern Namibia to give an early warning of armyworm attack. The traps are monitored every day and the catch of adult armyworm (moths) is recorded. Under normal circumstances, the figures are reported to the migratory pest control unit in Windhoek on a weekly basis. When more than 25 armyworm moths are found in a trap, however, the incidence should be reported immediately.
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