Fall armyworm

A newly established pest to Australia

Fall armyworm is a highly invasive pest that has recently become established in Australia.

Fall armyworm (FAW), Spodoptera frugiperda, is a highly invasive and destructive caterpillar native to tropical and subtropical regions of the Americas. (Figure 1).

A close-up photo of a fall armyworm.

Left unchecked, numbers can increase quickly due to abundance of suitable host plants, fast reproductive cycle and ability to disperse long distances.

Destruction of crops can happen almost overnight when population levels are high.

Since 2016 FAW has spread quickly through Africa, the Indian subcontinent, China and south-east Asia.

In January 2020 it was detected in far north Queensland and has since been found in northern Western Australia and Northern Territory. In September 2020, it was detected in a FAW surveillance trap near Moree in northern New South Wales. It is now considered established in Australia.

Despite multiple attempts, FAW has never been successfully eradicated from any country it has invaded.

Does fall armyworm occur in Victoria?

No. The current distribution of FAW in Australia is limited to the north of QLD, NT and WA. This pest prefers tropical and subtropical climates, which does not match the climate of Victoria’s production regions.

Given the ability of FAW to travel long distances, there is a potential for it to reach Victoria from time-to-time, most likely during warmer months (summer/autumn). It is not yet known if FAW will be able to establish in Victoria.

Key characteristics

Eggs are laid on the underside of leaves in masses of 100-300 usually with a protective cover of fine bristles (Figure 2).

Larvae of fall armyworm.

Newly hatched larvae (caterpillars) are 1mm long, pale greenish with a black head (Figure 3).

Fall armyworm egg mass.

Mature caterpillars are smooth bodied and grow up to 40mm in length. They range in colour from dark yellow to green, brown and black with prominent lighter stripes running the length of the body (Figure 4).

Illustrations of fall armyworm caterpillars.

Adults

Adults are dull brown and grey in colour with a large furry body and a wingspan of 32–40mm.

The male has two distinct white marks on each of the forewings (Figure 5 and 6).

FAW has a similar appearance to other armyworm species found in Victoria. The caterpillar can be distinguished by the inverted Y shape on the head.

The male adult has distinctive marks on the forewings and both adult sexes have iridescent white hind wings with narrow dark borders.

Fall armyworm with wings.

Fall armyworm moth at rest.

Impact of fall armyworm

FAW is known to feed on more than 350 plant species, including economically important crops such maize, cotton, rice, sorghum, sugarcane, wheat and many other vegetable and fruit crops.

Young caterpillars feed on leaves, creating pinholes and windows in leaf tissue, and giving leaf margins a tattered appearance.

Mature caterpillars can cause extensive defoliation and damage grazing on leaves stems and trunk and tunneling in to feed on fruit (Figure 7).

Many caterpillars may be present on one plant. If over-crowding occurs they will disperse en masse by "marching" in search of food (hence the name "armyworm").

Fall armyworm larvae are most active during late summer and early autumn months.

How does it spread?

Adults are capable of flying long distances and their migration rate is remarkably fast. They can also spread through trade and transport routes and people movement.

What do I do if I find fall armyworm?

Call the Exotic Plant Pest Hotline. 

Collect a specimen if possible. Place the caterpillar or moth in a glass or plastic container and refrigerate.Fall armyworm damage to maize crop.

If from your description, it is believed to be a fall armyworm a technical specialist may contact you for further information.

Control

FAW development and behaviour in the Victorian climate is not known to date. Issues such as whether FAW will persist through winter in Victoria, or migrate seasonally from warmer northern states, will influence control strategies. Economic thresholds for control are an area of current research.

The use of chemical control is an option where economic damage can be prevented. The APVMA has a broad range of chemical classes listed under emergency permits, additionally in Victoria off-label chemical use is possible under certain circumstances.

Beneficial insects can be prevented from becoming effective at reducing pest populations if broad spectrum insecticides are used in the production system.

To ensure safe and integrated pest management, consult a qualified agronomist for advice on chemical options that may include ‘softer’ options that will reduce harm to beneficials in your production system.

Photo credits

Figure 2 James Castner, Uni. of Florida

Figure 3 Pat Porter Texas A&M

Figure 4 Agricultural Research Council, Roodeplaat, South Africa

Figure 5 Lyle Buss, Univ of Florida

Figure 6 Kansas State Entomology, K-State Uni

Figure 7 G. Goergen.

Page last updated: 29 Oct 2020