How to Identify and Scout for Fall Armyworm

What is Fall Armyworm?

Fall Armyworm (Spodoptera frugiperda) is an invasive pest from the Americas that has become one of the most destructive pests of maize in Africa since its arrival in 2016.

Key Identification Signs

Egg masses: Found on leaf undersides, cream-coloured, covered with scales, laid in groups of 100–200.

Young larvae (1st–3rd instar): 1–10mm, greenish with a dark head capsule. Feed on leaf surfaces causing "windowing" damage.

Older larvae (4th–6th instar): Up to 45mm, brownish-green with a distinctive inverted "Y" marking on the head and four dark spots on the 8th abdominal segment.

Damage patterns: Ragged leaf holes, frass (excrement) in the whorl, bore holes into the stem, and feeding damage to cobs.

Scouting Protocol

• •Scout from 1 week after emergence
• •Check 10 plants at 5 random points = 50 plants total
• •Record: eggs present, young larvae (<10mm), old larvae (>10mm), % plants infested
• •Economic threshold: >20% plants infested with young larvae

When to Spray

Spray when young larvae (1st–3rd instar) are present and threshold is exceeded. Spraying against large larvae (>20mm) is far less effective. Target the whorl directly for best product placement.