Controlling Fall Armyworm in Maize and Sorghum

Fall armyworm (Spodoptera frugiperda) is the most economically significant pest of maize and sorghum across sub-Saharan Africa. Since its arrival in 2016, it has caused estimated losses of USD 2–6 billion per season if left uncontrolled.

Identification

Scout fields from crop emergence. Early instar larvae cause characteristic window-pane damage — they scrape the leaf surface without cutting through. Older larvae feed aggressively in the whorl, producing large, ragged holes and frass (wet sawdust). Look for the distinctive inverted Y marking on the head capsule of mature larvae.

Key signs:

• •Window-pane or pinhole damage on young leaves
• •Frass deposits inside the whorl
• •Wilted or dead heart in severe infestations

Scouting and Thresholds

Scout twice weekly during the vegetative period (V3–V8). Inspect at least 20 plants across 5 locations per field.

Action threshold: Treat when 20% or more of plants show whorl damage OR when young larvae are present in the whorl.

Chemical Control Options

Application Tips

• •Apply in early morning or evening when larvae are active at the whorl surface
• •Use high water volumes (300–400 L/ha) to ensure penetration into the whorl
• •For whorl applications, use a directed spray to improve product delivery
• •Add a crop oil concentrate or NIS adjuvant to improve penetration

Resistance Management

Fall armyworm develops resistance rapidly. Rotate between different IRAC mode-of-action groups:

• •Group 3A (Pyrethroids: lambda-cyhalothrin) → Group 1B (Organophosphates: chlorpyrifos) → Group 6 (Avermectins: emamectin benzoate)

Do not apply more than two consecutive sprays from the same mode of action group.

Safety Precautions

Wear full PPE when handling and applying: long-sleeved clothing, chemical-resistant gloves, goggles, and a dust/mist respirator. Re-entry interval is typically 24 hours. Keep all livestock and unauthorised persons out of treated areas.