Fall armyworm (FAW) [Spodoptera frugiperda] is an insect pest with moths as the adult stage and larvae (caterpillars) as the destructive stage.

In Kenya, the pest was first reported in March 2017 in Western Kenya and has since spread countrywide. The pest attacks a wide range of crops but maize and sorghum are the most preferred hosts. It can cause up to 100% yield loss if left uncontrolled.

This blog post provides information on the identification and management of the pest.

Identification of Fall Armyworm

Fall armyworm has 4 main stages of development: Egg, Larva, Pupa, and Adult.

The complete life cycle takes 40-47 days depending on the prevailing weather conditions. It takes short periods under warm conditions.

• Fall armyworm adult moths lay eggs in batches on host plants, normally on young leaves.
• The white egg masses are normally covered with wool-/ cotton-like material of the adult moth scales.
•  The larvae have 6 developmental stages (instars) that are the destructive stages and take the longest time in the life cycle.

Indicators of fall armyworm attacks

There are two ways of knowing whether a crop has a FAW attack:

1. Presence of any of the stages of fall armyworm (eggs, larvae, pupae and adults).
2. Damage caused by fall armyworm larvae on an infested crop.

How to identify FAW caterpillars

• The 1st instar larvae are very small and dark grey in colour. The 2nd and 3rd instars are greenish or yellowish-brown in color and have hair-like spikes.
• The 4th to 6th instars are brownish and have a characteristic light-colored “inverted Y” mark on the head front, which links with the middle thin stripe.
• There are 4 black dots in a square formation on the rear abdominal segment.

Damage Symptoms

• Young larvae (1st to 3rd instar stages) feed on leaves, causing transparent window pane-like damage, initially appearing as “scratch marks” on the leaf.
• Older larvae (4th to 6th instars) cause large ragged and elongated holes on leaves, leading to a shredded appearance.
• At the reproductive stages of the host plant, older larvae clip the tassels, make shot holes on ears and feed on grains.
•  Larvae produce large amounts of frass (excreta) as they feed and grow.

Monitoring and detection for timely action
♦ The pest can be noticed/detected in 2 ways: through the field scouting and use of pheromone traps.
a) Scouting in crop fields

• This involves walking in a systematic pattern looking for any crop damage, larvae, or eggs weekly (or more frequently), starting from crop emergence stage to the flowering stage.
• Look out for symptoms of damage and/or for the presence of pests as described earlier.
• Movement in the field during crop scouting can take a “V” or “W” pattern, stopping at several points depending on the farm size. See the example below

Movement pattern for scouting in a maize field – inspect 10-20 plants at each stop point.

b) Use of pheromone traps

•  This involves setting up traps containing pheromones (lures) that attract adult male moths.
• Captured adult moths are an indication of the presence of the pest and possible egg-laying.
• The PCPB website https://www.pcpb.go.ke provides the names ofFAW pheromones.

∼∼ Frequent monitoring and looking for fall armyworm and symptoms of damage is essential for effective management of the pest since observations guide timely action.

Management of fall armyworm

An integrated management approach (combining several intervention measures) should be applied. The following are the key measures that should be used in appropriate combinations for effective management of FAW:

1. Cultural control

• Plant at the onset of rains; late-planted and off-season crops suffer heavy infestations.
• Ensure maize fields are free from weeds and crop residues.
• Intercrop maize or sorghum with legumes (beans, cowpeas, green grams, Dolichos) to reduce the chances of the pest finding the host. This also enhances the population of natural enemie2.

2. Biological control

 Use Biopesticides registered by the Pest Control Products Board (PCPB) for the control of FAW.

 Conserve natural enemies of FAW such as: –

• Ladybird beetles that feed on eggs
• Lacewings that feed on eggs and larvae at early stages
• Birds that feed on larvae and pupae
• Bacteria, fungi, and viruses that cause the death of fall armyworm larvae

NB: Encourage responsible use of pesticides to avoid negative effects on natural enemies.

3. Use of insecticides

• If necessary and depending on the level of infestation, use appropriate insecticides that are registered for control of FAW by the Pest Control Products Board (PCPB).
• Spray late in the evening or very early in the morning when the larvae are active (not hiding).
• Direct the spray to the plant whorls (the funnel) and top leaves – use of a hollow-cone nozzle is recommended for spraying.
• Alternate chemical molecules with different modes of action to avoid the development of resistance to pesticides.
• If necessary, repeat sprays at two weeks intervals depending on infestation.
• Strictly harvest crops after the recommended pre-harvest interval (PHI) to avoid consumption of chemical molecules.
• Avoid spraying at physiological maturity.

NB: Ensure proper protective clothing is used to avoid exposure to harmful chemicals. 

Edited by: Z.M. Kinyua (Ph.D.) Head, Crop Health Research KALRO