Fall armyworm (FAW; Spodoptera frugiperda) was first detected in northern Queensland in early 2020 and has since become widespread within Australia. Documented as a polyphagous pest, FAW has so far demonstrated a preference for cereal plants with whorls, particularly maize (and sweet corn) and sorghum (both grain and forage crops), and can cause significant damage.

Identification

  • eggs are laid in ‘furry’ (scale covered) clusters of 100-200. They change from pale yellow to brown as the larvae develop.
  • larvae can vary widely in appearance and are at their most distinctive in later instar stages.  Neonates are translucent with a dark head capsule. Small and medium larvae vary from light green to brown, becoming darker with white lengthwise stripes and develop dark spots with spines as they grow. Older larvae are plump, can grow to up to 40mm long and have an inverted ‘Y’ shape on the head and a pattern of four large raised dark spots on the second to last body segment.
  • pupae are 15mm long and red-brown (similar in appearance but slightly smaller than helicoverpa pupae) and are found in the soil adjacent to host plants.
  • moths are about 16-17mm long, nocturnal, have a mottled brown or grey forewing, a white hind wing, and a wingspan of 32–40 mm. Male fall armyworms are more patterned and have a distinct white spot near the tip of each forewing.

Similar species

Young larvae can be difficult to distinguish from other species, including native armyworms, helicoverpa and cluster caterpillar (Spodoptera litura). Even medium to large larvae can be confused, with several native armyworm species also having an inverted ‘Y’ on their head, and helicoverpa larvae can display a similar pattern of raised dots (that become less prominent with age). Large FAW also have a plumper, greasier look than helicoverpa.

Life cycle

Eggs hatch in 3–5 days, and development though 6 instar stages to pupation takes 2–3 weeks at northern summer temperatures. Pupation takes another 2-3 weeks. Moths live for around 10 days, and a female can lay up to 1,000 eggs.

Crops attacked

Internationally, FAW has been reported from a wide range of crops. In Australia, FAW has been recorded (but not necessarily causing crop loss) in capsicum, sugarcane, millet, oats, Heliconium sp, strawberries, avocado, ginger, mungbean, soybean, green beans, wombok, celery, and Rhodes grass, with no infestations yet recorded from cotton.

Monitoring and management

Very susceptible crops (e.g. maize and sorghum) need to be closely monitored from emergence. FAW larvae can move from surrounding weeds or nearby crops to infest emerging cereal crops, doing substantial damage to young plants.

Look for the egg masses and clusters of young larvae, and signs of leaf damage. Eggs are typically laid on the underside of lower leaves (particularly the cotyledons) in establishing crops. Check in the whorl and around the plant base for larvae.

Leaf damage will be visible long after larvae have finished their development. The condition of emerging leaves (damaged/undamaged) is a better indicator of an active infestation than damage to fully expanded leaves.

A pheromone trapping network runs from spring to mid-summer in Queensland and New South Wales to provide an indication of moth migration into production areas. Counts are published on the Beatsheet.

Screening by NSW DPIRD of the Australian FAW populations has identified moderate resistance to carbamates and organophosphates and high resistance to synthetic pyrethroids. Ongoing monitoring of resistance levels and implementation of resistance management strategies will be essential to minimising the risk of resistance development in Australian FAW populations.

Several predators, parasitoids and pathogens have been identified from FAW in Australia, including egg parasitoids (Trichogramma sp and Chelonus sp.), larval parasitoids (Cotesia sp, Tachinid flies), pupal parasitoids (Heteropelma sp.), predatory bugs, spiders and pathogens (Metarhizium rileyi).

Commercial formulations of FAW-specific nucleopolyhedrosis virus (Fawligen® and Spodovir® Plus) are available under permit for FAW control in a number of crops. Check the product documentation/label for specific instructions regarding appropriate use.

Further FAW information

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