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Oriental Armyworm

Insect

Mythimna separata


In a Nutshell

  • Feeding damage in seedlings, leaves and cobs.
  • Saw-like appearance on leaves.
  • Wet, brown frass lines near feeding damage.
  • Premature defoliation.
  • Reddish brown moths with thoracic hair, grayish yellow forewings, hindwings are blueish gray.

Symptoms

The caterpillars feed on young seedlings or leaves. At later stages they also attack young cobs. They preferably eat leaf tips and margins and feed toward the midrib, giving the leaf a saw-like appearance. Wet, brown lines of frass can be observed near the feeding damage. Defoliation can occur when the population is high. Direct damage to cobs usually is negligible because the pest usually attacks upper plant parts only when the lower leaves have largely been consumed. After defoliating a crop, they migrate in large groups to other fields, thereby their common name. Alternative hosts such as grasses can also favor their spread.

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Hosts

Trigger

Adult moths are light to reddish brown with a wingspan of 4-5 cm and thoracic hair. Their forewings are grayish yellow and scattered with black specks. They have two small clear spots with an indistinct edge in the center. Their hindwings are blueish gray with dark veins and dark external margins. Adults are nocturnal and strongly attracted to light. Females lay pale, creamy eggs under the leaves. They survive better and produce more eggs when temperatures are above 15°C. Caterpillars are stout and usually pale greenish to brown in color. They have longitudinal stripes running along the body with the ones on the flanks being broken into black spots. They are nocturnal and thrive in well fertilized fields. Favorable conditions for an outbreak include prolonged dry periods followed by heavy rainfall.

Organic Control

Braconid wasp Apanteles ruficrus and tachinid flies Exorista civilis parasitize on the larvae and can successfully reduce pest population and the incidence of the disease. Spinosad has also been used effectively in baits to kill the adults. Another biological control measure are the pathogenic fungi Beauveria bassiana and Isaria fumosorosea. They colonize and kill the larvae.

Chemical Control

Always consider an integrated approach with preventive measures together with biological treatments if available. Pesticides should be applied only if the infestation is severe. Cypermethrin can be sprayed against the larvae, preferably later in the day. Whorl application some insecticides at 25 - 30 days after germination also effectively helps to control the armyworm populations. Poison baits containing chlorpyriphos can also be used.

Preventive Measures

  • Adjust the time of sowing to avoid peak populations.
  • Check your plants regularly for any sign of the pest.
  • Handpick the larvae found in plants.
  • Use light or pheromone traps to monitor infestations.
  • Control weeds in and around the fields.
  • Dig trenches around infested plots to control the movements of the larvae.
  • Flood the seedbeds to drown the larvae.
  • Remove crop residues from the field and burn them.

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