Fall armyworm

Fall armyworm (FAW, Spodoptera frugiperda) is an exotic pest that was first detected on the Australian mainland  in February 2020. State and federal biosecurity organisations have determined it to be unfeasible to eradicate this pest and it is now classified as an endemic pest.

On this page:

• FAW identification
• FAW damage
• FAW distribution and management (including online Q&A session)
• The potential impact of fall armyworm on winter cereal crops in the Northern Grains region
• Other resources

Identification

Many leaf-eating caterpillars share similar visual characteristics and damage symptoms. FAW larvae are most distinctive when fully grown; distinguishing younger larvae can be more difficult. It is important to not rely on a single characteristic when identifying larvae – a correct identification is more likely when multiple characteristics are considered.

	Download Identifying armyworm larvae (May 2020 – 4MB A3 pdf)
	Download a Fall armyworm diagnostics presentation by Mark Schutze (DAF, Plant Biosecurity Laboratory) – 2MB pdf
	Where live insect collection is impractical, high quality photos, including close-ups are essential to provide the best chance of identifying the specimen. Download a Caterpillar identification: taking photos factsheet (600kB PDF).
	The FAW pheromone traps currently used have the potential to attract a range of insects. Read our guide on how to sort the by-catch from the potential FAW moths (1MB pdf). Watch a video on sorting and processing potential FAW moths.

Damage

How do FAW and other caterpillars eat holes in leaves without being seen? Take a look at our short video below on FAW shotgun damage in maize.

Distribution in Australia

Fall armyworm has been confirmed in Queensland at Bamaga, Croydon, South Johnstone, Tolga, Lakeland, the Burdekin, Bowen, Bundaberg and Emerald. It has also been detected in the Northern Territory and northern Western Australia.

Management

At this stage, management suggestions are based on overseas information since how FAW will manifest as a pest species under Australian conditions is currently unknown. More detailed information will be made available as we lean more about this pest, its behaviour and impacts under local cropping systems.

See our Beatsheet article Fall armyworm – should you be concerned? (5 March) for more details.

Thresholds based on overseas data:

Crop	Threshold	Notes
Maize vegetative   Maize whorl stage	3 or more larvae per plant *50% of plants with fresh feeding20% of plants with one or more larvae *>75% of plants with feeding	Based on US recommendations: *Purdue UniversityNeed to consider economics of control i.e. $/ha to treat vs potential yield loss ($/ha).
Sweet corn Tassel emergence	15% of infested plants	US recommendations: If necessary, control at tassel emergence is more effective than applications in the vegetative stages.
Sorghum vegetative Sorghum grain fill	30% defoliation, or >2 larvae per whorlUse helicoverpa threshold calculator	Based on US recommendations. Damage at grain fill equivalent to Helicoverpa.
Cotton	–	Monitor crops for leaf damage and fruiting site feeding. Bollgard 3 will incidentally suppress FAW.
Soybeans vegetative Soybean budding-podding	33% defoliation 3/m2	Based on S. litura (DAF)
Pasture (hay production only)	2-3 larvae /sq foot	No permits currently. Armyworm outbreaks (other species) not uncommon.

FAW Q&A session (CQ Grower Solutions)
Online presentation and Q&A session organised by CQ Grower Solutions on 6 May 2020, featuring Melina Miles (DAF) and Brent Wilson (Nutrien Ag Solutions, Home Hill). Due to technical issues the initial audio of Brent’s presentation has been re-recorded by Melina. Download the Q&A summary (775kB pdf)

Fall armyworm was also discussed in an online Seasonal Update on 27 May 2020. See our presentations page for more information.

The potential impact of fall armyworm on winter cereal crops in the Northern Grains region

Winter is here, and not just any winter, but the first in which fall armyworm (FAW, Spodoptera frugiperda) in included in the pest complex in the Northern Grains Region. But given FAW is described as a tropical pest, what is the potential impact on winter cereals in Queensland and northern New South Wales?

Host availability and suitable temperature regimes are likely to be the key. FAW’s wide host crop range overseas suggests that regions with both summer and winter crop options, or persistent green bridges between seasons, are favourable environments for year-round populations. However, observations on host selection by FAW in Australia to date show a strong preference for corn, sweet corn and sorghum. Infestations in chickpeas and soybeans in the Burdekin have resulted in only superficial foliage feeding. In addition, overseas experience shows that FAW populations decline at temperatures below ~25℃, and typically do not survive once temperatures fall below 10℃. It is possible that CQ will be the southern-most extent of the year-round population of FAW, but autumn movement of FAW moths could put more southerly crops at risk of early defoliation.

Recent modelling by Queensland Department of Agriculture and Fisheries (DAF) Economist, James Hagan and Principal Entomologist, Dr Melina Miles has attempted to estimate the likely impact based on the best information currently available. The modelling looks at the risk to early sown cereals that establish under temperature regimes considered suitable for FAW activity.

Using typical soil types from Capella to Goondiwindi, and assuming a full profile of water was available, the modelling integrates historical climate data to identify how often there was likely to be an early planting opportunity for wheat, and in those scenarios what sort of damage occurred prior to the weather being too cold for FAW survival. Leaf damage was estimated for 5^th and 6^th Instars (which account for 80% of crop damage) at 25-30 mg/larvae/day, with low (10) medium (30) and high (60) FAW larvae per square metre.

The model indicates that there is a very narrow window in some regions (where there was overlap between expected FAW activity and early sowing opportunities). However, unless sown into an area where FAW pressure is already high, it is unlikely there will be a measurable impact on yield of winter crops.

 

Site	Estimated date too cold for FAWa	Early Plant Opportunityb (%)	Potential yield reduction (kg/ha)
			10 FAW/m2	30 FAW/m2	60 FAW/m2
Capella	15-Jun	35%	8	32	65
Biloelac	5-Jun	30%	0	–	–
Theodore	4-Jun	30%	17	30	44
Roma	1-Jun	25%	0	15	24
Warra	20-May	10%	0	0	0
Goondiwindi	10-May	15%	0	0	0

a The date that in 80% of years the previous 5 days have all had minimums below 10 degrees.
b The likelihood that a planting opportunity will have occurred (30mm over 3 days) assuming an existing full profile, prior to being too cold for FAW based on last 20 years of climate data, and crop sowing guide planting windows for the earliest available varieties.
c At Biloela, FAW larvae feed demand at medium and high density scenarios outstripped expected total crop biomass, causing potential for total crop loss, however this would mean the number of larvae couldn’t physically exist on these plants to cause said crop loss.

This modelling is based on the best information currently available, and work is underway to better understand FAW behaviour in Australian grain growing environments and crop species.

Other resources

Queensland’s Department of Agriculture and Fisheries (DAF) has a range of crop-specific factsheets.

The GRDC has a Fall armyworm: a crop invader on the march page with identification information and links to other resources.

CropLife Australia has released a FAW resistance strategy.

CottonInfo has a short video highlighting some of the similar characteristics between caterpillars and an Endemics to exotics factsheet that looks at some of the differences between armyworm species found in the tropics.

A range of spray permits for fall armyworm are now available. Search for permits relevant to your crop/situation at the APVMA website.