Fall armyworm

Primefact number Edition Published Author
1722 Second Oct 2020 Plant Biosecurity and Product Integrity

egg mass covered by light brown silk-like furry substance, on a green leaf of a corn plant

Brownish grey caterpillar eating holes through the leaves of a corn plant

A green leaf with a long thin caterpillar on the leaf surface. The caterpillar is light brown with whitish stripes and a very dark brown head

A light brown moth with varied brown and white markings on forewings and white hindwings with light brown markings on margins

Fall armyworm (Spodoptera frugiperda) is an insect pest that has been detected in NSW.

This insect pest is a serious threat to a wide range of industries including grain, rice, cotton, vegetables and sugarcane.

Current situation

Updated: 20 October 2020

Since 2016, fall armyworm has been spreading rapidly across the globe and was expected to impact Australia. It was detected in the Torres Strait and North Queensland in January/February 2020, and Katherine, NT and Kununurra, WA in March 2020. Further detections in WA in April occurred at Broome and Carnarvon.

The pest was first detected in NSW on 23 September 2020 north of Moree. Subsequent detections were made east of Narrabri and west of Wee Waa in October 2020.

It is anticipated that the pest will impact NSW summer cropping with flights moving into NSW from northern states. Some feeding damage has been observed in maize in the Namoi valley.

The Consultative Committee on Emergency Plant Pests, consisting of industry, the Commonwealth, state and territory governments, agreed that fall armyworm is not technically feasible to eradicate in Australia.

Government is working to prepare potentially affected industries for ongoing management of the pest. As part of this, NSW DPI is working with LLS and other collaborators to establish an early warning trapping grid across the north of the state. The moth found on 23 Sept 2020 was captured by this grid. Growers in the Macintyre, Gwydir and Namoi valleys especially are urged to be on high alert for signs of fall armyworm laying and damage in their crops.

DPI continues to work with potentially affected industries providing free insect diagnostics for suspect fall armyworm moths and larvae, advice on control and chemical management options. At present, maize crops have been damaged by the pest in the north of Australia but it is not known how badly the pest will impact on maize and other crops in NSW.

Webinar

A webinar was held in April to discuss the current situation in NSW, biology and damage caused, identification, surveillance activities, how to report, and chemical control options. The webinar was recorded and can be viewed as an entire playlist or separate videos (link directs to www.youtube.com).

Notifiable status

Fall armyworm (Spodoptera frugiperda) is a notifiable plant pest in NSW.

All notifiable plant pests and diseases must be reported within 1 working day.  You can report notifiable plant pests and diseases by one of the following methods:

A full list of notifiable plant pests and diseases can be found in Schedule 2 of the NSW Biosecurity Act 2015.

Description

Fall armyworm is the name commonly attributed to the larval stage of the moth Spodoptera frugiperda. Other Spodoptera species already found in Australia include the lawn armyworm and the dayfeeding armyworm.

The fall armyworm life cycle has an egg stage, 5 to 6 caterpillar (larval) stages, a pupal stage and an adult moth stage. The larval life cycle stages cause widespread damage to crops through feeding.

Fall armyworm eggs are usually laid on the under surface of leaves in clustered masses of 100-200, covered with a ‘felt like’ layer of scales (Figure 1). The eggs are pale yellow.

Small fall armyworm larvae are usually light green to brown, with a dark head capsule. Evidence of crop damage, such as the skeletonising of leaves (or ”windows”) is often more readily visible than the presence of larvae (Figure 2).

Large fall armyworm larvae grow to 3-4 cm, becoming darker as they mature, with pale white stripes along the length of the body (Figure 3). The large caterpillars have a pale inverted “Y” shape between the eyes. Two dark spots with dark spines occur on each body segment on the upper body surface, with 4 black spots arranged in a square on the last abdominal segment.

Fall armyworm larvae normally pupate in the soil. The pupae are shiny brown and between 1.3 and 1.7 cm long.

Adult fall armyworm moths measure 3-4 cm from wingtip to wingtip. Female moths are slightly larger than males, although both sexes have a white hindwing with a dark-brown margin. Male moths are more patterned and have distinct triangular white spots at the tip and near the centre of each forewing (Figure 4).

Damage

Fall armyworm damage in many crops has similar symptoms to that caused by other larvae. If you find crop damage symptoms, carefully examine the plants for larvae to identify which species are present.

Life cycle

Fall armyworm can complete its life cycle within 23-27 days (from egg laying to the emergence of adult moths), when suitable temperatures and host plants are present.

The eggs hatch within 2-4 days after being laid on the lower leaf surfaces. After hatching, fall armyworm larvae complete 5 to 6 growth stages within 14-22 days of hatching to reach maturity. Once mature, larvae drop to the ground, where they pupate for around 8-9 days in warmer months and 20-30 days in cooler areas.

Female moths lay most of their eggs within 4-5 days of mating, but can continue laying for up to 2 weeks. As fall armyworm does not diapause (suspend development) during the pupal stage, populations are unlikely to establish in areas where temperatures fall below 9-12⁰C and where frosts occur.

Host range

Fall armyworm larvae feed on more than 350 plant species, with a preference for grasses. Key hosts include cotton, maize, rice, sorghum, sugarcane, wheat and vegetable crops like sweet corn.

The current strain in Queensland has been observed causing significant damage to maize. It is not currently known how many other plant species will be preferred food sources for this new pest.

Spread

Adult fall armyworm moths are strong flyers and will travel hundreds of kilometres on storm fronts. The larvae can also be spread in cut flower, fruit and vegetable consignments.

Distribution

Fall armyworm is native to the tropical and sub-tropical regions of the Americas. In early 2016 it was detected in Central and Western Africa and quickly spread across sub-Saharan Africa. By December 2018, it was found in the Indian subcontinent. In June 2019 fall armyworm was reported in China and Southeast Asia.

Fall armyworm is currently present in Australia. It has been found in Queensland, Northern Territory, Western Australia and northern New South Wales.

Actions to minimise risks

Put in place biosecurity best practice actions to prevent the entry, establishment and spread of pests and diseases:

  • practice “Come clean, Go clean”
  • control weeds and volunteer plants in fallow paddocks, along fence lines and around buildings to reduce the number of pest hosts
  • monitor crops regularly for signs of armyworm damage
  • report anything unusual to 1800 084 881
  • keep records

Resources