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Paddy armyworm on rice

Mythimna separata Fauzi kira
  • Rotate rice with vegetables as rice and other cereal crops are major hosts of paddy armyworm.
  • Control grassy weeds in the rice field as they are alternative hosts.
  • Conserve natural enemies such as Cotesia or Trichogramma wasp, and Carabid ground beetles by reducing pesticide use and growing flowering plants along border.
  • Apply recommended dose of nitrogen fertilizer (100 kg N /ha) as too vigorous growth can increase armyworm infestation
  • Use 2-5 light traps/Ha at the edge of the field and examine traps weekly for moths.
  • After observing first moths in light traps, start monitoring the rice plants weekly to check caterpillar damage in crop (massive leaf removal, often including leaf veins) as damage occurs suddenly.
  • Stout, hairless and brown caterpillars with a narrow, white dorsal line. Caterpillar curls to form C shape if disturbed.
  • During grain filling stage, the larger caterpillars cut off panicles at their base causing some to bend while others to fall to the ground.
  • Apply control measures if 1-5 larvae/hill during pre-panicle stage and 1 larva/hill at panicle stage are observed.
  • Hand-pick egg masses (laid in single or double rows between the base of the leaf sheath and stem, which are not covered with hair) or larvae from seedbeds or a young crop and destroy them.
  • Flooding of the nursery bed/ main field and dragging ropes across the top of the rice plants to detach and drown the swarming larvae.
  • Use insecticides to control the larval stage. Do not mix pesticides. Alternate insecticides to avoid pest resistance development.
  • When using a pesticide or botanical, always wear protective clothing and follow the instructions on the product label.
  • Always consult recent list of registered pesticides from Pesticide Registration and Management Division, Nepal (
  • Spray Azadirachtin –products, IRAC Group UN, Multi site action.
  • Toxicity not classified by WHO, but unlikely to present acute hazard in normal use. Restricted re-entry interval (r.e.i.) 1 day after spray. Max 3-4 sprays per season at minimum 7 days interval.
  • Bacillus thuringiensis (take Lepidopteran larvae active strain), IRAC Group 11A, Secondary contact action but pests need to ingest it.
  • WHO toxicity class III (slightly hazardous). r.e.i. 1 day after spray. Max. 3-4 sprays per season at minimum 7 days interval. Selective pesticide, thus less harmful to non targets.
  • Spray Cypermethrin –products, IRAC Group 3A (Pyrethroids), broad- spectrum insecticide. Non-systemic with contact and stomach action on caterpillar
  • WHO class II (moderately acute hazardous). r.e.i. 1 d after spray. Max. 2 sprays per season at min 14 d interval. Do not spray during day time (toxic to bees). Do not spray near water sources (harmful to aquatic organisms).
  • Spray Chlorpyrifos –products IRAC Group 1B (Organophosphates)(250 ml/Ha), broad- spectrum, contact insecticide with knockdown effect.
  • WHO class II (moderately acute hazardous); r.e.i. 1 day after spray. Max. 2 sprays per season at min 14 d interval. Toxic to beneficial insects, bees, aquatic organisms.
AUTHOR(S): Chhetri, Purnima (Pesticide Registration and Management Division, Nepal)

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