Fall armyworm

Fall armyworm: a crop invader on the march

Key points

  • Fall armyworm was first found in Australia in northern Queensland in January 2020 and has since spread.
  • Australian biosecurity organisations have determined it is unfeasible to eradicate.
  • Early identification will assist in reducing its impact.
  • Report any suspected sightings of the pest immediately to the Exotic Plant Pest Hotline 1800 084 881.
  • Its larvae can feed on many crop species, including maize, sorghum, pulses, winter cereals, sugar cane, rice and cotton.
  • It has a strong preference for maize crops and can be highly destructive when not controlled.
  • It is a migratory species that utilises prevailing winds; it can also be spread by humans on infested plant materials.
  • It has become resistant to many chemical treatments.
  • An Integrated Pest Management (IPM) program is the best management approach, combining careful selection of insecticides with natural enemy conservation and good agronomic practices.

Summary

Fall armyworm (FAW), Spodoptera frugiperda, was first detected in the Torres Strait in late January 2020 and then in Queensland's Cape York area and the north west Gulf region in February. Following additional confirmed detections Australian biosecurity organisations have determined it is unfeasible to eradicate. FAW detections reported in March 2020 included Bowen and the Burdekin in Queensland. FAW detections reported in April 2020 (to 23 April 2020) have included Bundaberg and Emerald in Queensland; Darwin, Katherine and Douglas Daly regions in the Northern Territory; and Kununurra and Broome in Western Australia.

Native to tropical and sub-tropical areas of the Americas, the pest has spread across two continents and more than 60 countries in under three years.

Figure 1. Map of the worldwide spread of fall armyworm since 2016 (as of 21 April 2020)

Map of the worldwide spread of fall armyworm since 2016

Source: FAO: compiled from information provided by FAO, International Plant Protection Convention, CABI, European and Mediterranean Plant Protection Organization and national governments. This map has been adapted by GRDC to reflect FAW detection in northern Queensland.

It feeds on a wide range of plant species and has the potential to damage important crop species including maize, sorghum, soybean, winter cereals, peanuts and sunflowers, as well as cotton and sugarcane.

Later stage larvae can be highly destructive, severing seedlings, or causing defoliation or damage to reproductive structures.

Fall armyworm has a high reproductive rate and dispersive capability. Females can produce up to 2,000 eggs in their lifetime; some estimates suggest that they can travel around 100km in a night and 500km in a generation.

Figure 2. The life cycle of the fall armyworm
Cycle completes every 24-40 days depending on the temperature

The life cycle of the fall armyworm

Image Acknowledgements: Lyle Buss and James Castner, University of Florida and Matt Bertone, NCSU.

Adult moths are nocturnal and most active during warm, humid evenings. Based on overseas information, the larvae are most active during late summer and early autumn, however they can be active year-round in tropical areas.

Insecticide use should be considered as part of an overall IPM program. There is evidence that resistance in the pest’s native range is widespread. Early identification and treatment of economically significant infestations as part of an IPM program will minimise damage to Australian crop production.

No affected country has managed to eradicate the pest to date. In other countries, biological control (predators, pathogens and parasitoids) has been a key component of managing this pest. It is likely that natural enemies already existing in our agroecosystems will offer some control of this pest.

Initial forecasting has predicted that fall armyworm infestations could be severe in the first few years following the incursion. Existing natural enemies may take some time to adapt to this new pest – the use of pesticides may disrupt this process.

It is likely that management of FAW will improve as industries become more confident and experienced in dealing with the pest within Australian farming systems.

What does fall armyworm detection mean for broadacre crops in Australia’s grain growing regions?

Areas of northern Australia (tropical and sub-tropical) areas are likely to host FAW populations in crops, pastures and weeds/native grasses.

At this early stage, it is difficult to know how significant a pest FAW will be in different crops and regions. It is challenging to predict how Australia’s climatic and vegetation zones will influence the timing and magnitude of FAW migrations.

In the United States, FAW is most common in the southern (warmer) states of Texas and Florida with northern occurrences attributable to migrations during late summer and early autumn.

Figure 3. The global and Australian potential distribution of fall armyworm (Spodoperta frugiperda) modelled using CLIMEX

The global and Australian potential distribution of fall armyworm (Spodoperta frugiperda) modelled using CLIMEX

The global and Australian potential distribution of fall armyworm (Spodoperta frugiperda) modelled using CLIMEX

Legend

  • Yellow-red shaded: areas indicate relative climatic suitability for establishment of persistent populations.
  • The green-shaded: areas indicate climatic suitability for seasonal migration during the warmer months.
  • Pink areas: cannot support a full generation of the moth.

It is likely that persistent populations will occur from central Queensland northwards, with annual (or sporadic) migrations further south. It is possible that southern migrations could damage establishing winter crops.  If it follows a similar geographic range to S. litura, it is unlikely to become a major pest in Victoria or South Australia.

Populations will not survive frosts or temperatures below around 12℃.  It is estimated that a minimum of 600 day degrees (above 12°C) are needed to complete a generation.

In its native range, fall armyworm is often referred to as comprising two subpopulations (rice and corn strains) that look the same and can interbreed, but differ in their distribution, host plant preference and certain physiological features. Due to hybridisation these classifications are unlikely to be useful indicators of host preference in Australia.

At present (mid April 2020), confirmed detections have been primarily in maize, sorghum and sweet corn.

How do I identify fall armyworm?

There are other pests already present in Australia which look similar to fall armyworm.

The following diagram and ID guide will assist you in identifying common armyworm, cluster caterpillar, northern armyworm and fall armyworm that may co-occur.

Figure 4. Identifying features of a fall armyworm larva

CAUTION: Some individual features (eg inverted ‘Y’ on head) are shared by other species; larvae display considerable variation in colour and patterning.

Identifying features of a fall armyworm larva

For more information watch Dr Mark Schutze, QLD DAF, talk through fall armyworm identification in detail.

Identification of fall armyworm and comparison with other species similar in appearance

Cluster caterpillar

The Cluster caterpillar (Spodoptera litura) is also known as the cotton leafworm or tobacco cutworm.

Found across Australia but more prevalent in tropical regions.

Host: broad host range – cotton, sunflower, soybean, mungbean, navy bean, canola, peanut, chickpea, faba bean, safflower, linseed, adzuki bean and lucerne and broadleafed weeds.

Eggs

  • Eggs are spherical, pale-pink and 0.6mm in diameter.
  • Eggs are laid in clusters of up 300 on leaves
  • Clusters are covered in a layer of pale-brown ‘furry or cottony’ hair-like scales
  • Up to 50mm in length

Cluster caterpillar larvae eggs.  Image: P. Grundy, Qld DAF.

Cluster caterpillar larvae eggs.  Image: P. Grundy, Qld DAF.

Young larvae

  • feed in groups on the lower leaf surface causing a ‘window’ effect
  • are translucent green with a dark thorax and head

Young cluster caterpillar larvae.

Young cluster caterpillar larvae.  Image: J. Wessels, Qld.DAF.

Mature larvae

  • Have a row of black dots along each side, as well as a row of half moon-shapes (triangles) along the back
  • Older larvae are solitary and have obvious black half-moon shapes (triangles) in a line along the sides of their bodies
  • Pale yellow inverted ‘Y’ on the head
  • Have three thin pale yellow/orange lines running down the length of the body.
  • Pupate in the soil

Medium sized cluster caterpillar larvae.

Medium sized cluster caterpillar larvae.  Image: J.Wessels, Qld.DAF.

Mature cluster caterpillar larva.

Mature cluster caterpillar larva.  Image: Paul Grundy, Qld.DAF.

Moth

  • Wingspan of 30-38mm
  • Brown forewings with brown, red and dark grey markings with silver/light coloured marbling patterns
  • Hindwings are white and partly translucent with brown edge

Cluster caterpillar moth – male

Cluster caterpillar moth – male (lef) and female (right). Image:  J.F Germain

Cluster caterpillar moth –  female

Cluster caterpillar moth and eggs.

Cluster caterpillar moth and eggs.  Image: J.Wessels, Qld.DAF.

Common armyworm

Northern armyworm

Fall armyworm

If you suspect fall armyworm call the Exotic Plant Pest Hotline on 1800 084 881.Exotic Plant Pest Hotline

For more information contact the Department of Agriculture in your State or Territory.

What crops are most at risk?

Maize and sweet corn

Maize is a highly preferred host of FAW and has a relatively high risk of crop losses. Sweet corn is even more high risk because of low market tolerance for damaged cobs. In addition to yield loss, affected ears are more likely to develop fungal diseases and the production of aflatoxins, affecting grain quality. Likewise, damage to maize cobs during grain filling can impact yield and grain quality by allowing entry of fungi and bacteria.

Larvae feed on the maize leaves, creating ‘windows’ (irregular, elongated holes). Larger larvae establish themselves in the whorl where they can damage the growing point, with larvae also feeding on reproductive structures as they develop. Moths may shelter in the whorl during the day. Where heavy infestations occur, frass (insect droppings) will be visible on leaves and in the whorl. If damage is evident, but larvae are not visible in the foliage, check in the whorl. If the larvae damage the growing point inside the whorl the plant will be unproductive and may die.

As maize can be attacked at all growth stages, crops need to be checked regularly up until maturity. Rapidly growing plants can tolerate some defoliation in the vegetative stage, but significant loss of leaf between V6-R1 will impact on growth and yield.

Damage to leaves, the whorl and cobs, can look similar to the damage caused by Helicoverpa armigera, common armyworm (Mythimna convecta) and cluster caterpillar (Spodoptera litura). Cluster caterpillar has been observed laying eggs on the lower leaves and small larvae ‘windowing’ these leaves before moving up on maize plants.

Fall armyworm can also sever seedlings at the base, similar to cutworm damage. It is advisable to open the whorl and carefully examine for larvae to determine which species are present.

Fall armyworm is not susceptible to the same nuclear polyhedrosis virus (NPV) used to control H. armigera in maize and sweet corn.

Sorghum

Cotton

Pastures

What should growers do?

1 - Be vigilant and monitor

The best way to minimise the spread and impact of FAW is to identify signs of infestation early. Sightings of suspected eggs, larvae and moths should be reported immediately to the Exotic Plant Pest Hotline on 1800 084 881 or if located in Queensland to 13 25 23.

FAW can be confused with a number of armyworm and other caterpillar species present across Northern Australia.

Use the identification resources included on this page.

Symptoms of infestation include sudden crop damage and collapse, leaf damage such as pinholes, windowing, tattered leaf margins, skeletisation and defoliation of plants. Tiny larvae (less than 1mm) are more active at night and leave pin holes and transparent windows in leaves while bigger larvae graze on leaves, stems and fruiting structures and leave behind excrement.

As FAW pheromone traps become available to industry, they will be a useful early warning of local moth activity and seasonal risk.

The APVMA permit PER89169 allows the use of specified products for fall armyworm pheromone monitoring traps. Permit approvals can and do change regularly – consult the APVMA website and follow all permit instructions.

2 - Control and treat - available permits

3 - Maintain good on farm biosecurity practices

The industry response

GRDC is collaborating with other plant-based research and development corporations, the Department of Agriculture, Water and Environment, the Queensland Government Department of Agriculture and Fisheries and Plant Health Australia to ensure an effective response.

Research is focusing on understanding the pest status of this insect within Australian production systems to identify and develop a range of effective management practices (cultural, biological and chemical).

Focus will also be on minimising the risk of insecticide resistance development, particularly in other related pests.

Through the Plant Biosecurity Research Initiative, the GRDC and other plant-based RDCs are working to co-ordinate a cross-industry response and the submission of permit applications for insecticides to the APVMA.

GRDC is investing in work to characterise the pest; estimate potential impacts and develop management options; and identify and prioritise RD&E gaps.

QLD DAF webinars

Useful resources

Frequently asked questions

Could Fall armyworm populations be found in a range of climatic zones in Australia?

As FAW has spread across the world it has been identified in more temperate regions. Researchers are working to establish how it might behave in Australia but at this stage all growers are asked to be vigilant.

Are we close to any resistant crop varieties or biological-based pest controls?

Internationally there are biological products available and there have been some levels of host plant tolerance identified during research. Transgenic Bt (Bacillus thuringiensis) maize varieties are grown in various parts of the world and afford some level of resistance against FAW. Bt maize is not grown in Australia. Resistance to various Bt Cry toxins such as the Cry1F toxin used in Bt maize is known in FAW from the Americas.

What did industry do to prepare for a potential incursion?

GRDC applied for pre-emptive chemical permits for FAW with the APVMA; the first permit was issued in April 2018 and the second in February 2020.

When FAW was found in Far North Queensland, biosecurity measures were quickly implemented including traps, monitoring and the establishment of a taskforce to guide effective communication with industry.

Does fall armyworm keep reappearing in the same crop?

As with most insect pests, left uncontrolled FAW will feed on a host until the food source is exhausted after which the pest could move en-masse to nearby hosts (potentially neighbouring crops). As it can attack at varying stages in crop growth, ongoing control is likely to be required.

More information

GRDC Contacts

Queensland Department of Agriculture and Fisheries Contacts

Phone: 13 25 23 or Dr Melina Miles, Principal Entomologist - Queensland Department of Agriculture and Fisheries – Melina.Miles@daf.qld.gov.au

Exotic Plant Pest HotlineExotic Plant Pest Hotline

Exotic Plant Pest Hotline 1800 084 881

Acknowledgements:

Melina Miles (Qld. DAF), Sharna Holman (Qld DAF), Haidee Brown (DPIR NT), Tek Tay (CSIRO), Susan Maas (CRDC), Tonia Grundy (Qld. DAF), Olivia Reynolds (cesar), Jodie Pedrana (Hort Innovation), Boris Castro (Corteva), Darren Kriticos (CSIRO), Samantha Allen (Qld. DAF), Ruth Redfern (CRDC), Daniel Rodriguez (UQ) and Myron Zalucki (UQ)