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23 July, 2020

Fall armyworm strikes Highlands, Central West, Callide

Longreach has joined Biloela, Emerald, Clermont, Richmond, and several areas in North Queensland as the latest to fall victim to the invasive and highly destructive moth pest, fall armyworm, with warnings now being issued about its effect on pastures.


The Queensland Primary Industries Department has issued urgent warnings to landowners throughout Central and North Queensland. “Be on the lookout and if you suspect fall armyworm, report immediately by phoning 13 25 23.”

When the moth was first detected on the Australian mainland in January, Biosecurity Queensland General Manager Plant Biosecurity and Product Integrity, Mike Ashton, said fall armyworm was an invasive moth pest that fed in large numbers on more than 350 plant species.

“Fall armyworm causes major damage to economically important cultivated grasses such as maize, rice, sorghum, sugarcane and wheat, and also to other horticultural crops and cotton,” Mr Ashton said.

The DPI website now emphasises that fall armyworm is reported to feed on tropical and subtropical grasses in grazing systems overseas. It is likely that tropical and subtropical pastures in Queensland will support large populations of fall armyworm in suitable seasons.

The website says it is unclear what impact fall armyworm might have on pasture productivity, but outbreaks of day-feeding armyworm (Spodoptera exempta) have caused significant short-term defoliation in buffel pastures.

This defoliation can kill seedlings and retard the growth of established plants. Infested pasture may be reinfested by the offspring of the first infestation.

Grasses that fall armyworm infest overseas include: Sorghum haleepense, common name Johnson grass; Chloris gayana, common name Rhodes grass; Agrostis spp., collectively called bent grasses; Digitaria spp., collectively known as pangloa, digit or finger grasses; Cynodon dactylon, common names include couch, green couch, couch grass; Poa spp., common names in Queensland include annual Poa, winter grass; and Panicum spp., collectively known as panics.

Most of these are common across Queensland, in grazed pastures, hay production, and urban situations.

The potential for fall armyworm to infest other important native (e.g. Mitchell grass, spear grass, blue grasses) and sown pastures (e.g. Buffel grass, Rhodes grasses) is unclear, but it is possible these could host.

Hay production, including lucerne, may be at risk of production loss caused by fall armyworm infestation, including irrigated production over winter in warmer regions.

Last Thursday the Federal Government announced it had provided Plant Health Australia with a $600 000 grant to coordinate a national strategy against the fall armyworm threat. Minister for Agriculture David Littleproud said the funding would bring together local and international experts, research organisations, government and industries to identify knowledge gaps.

“The outcomes of an industry workshop will inform the development of a national management plan and guide investment in projects for monitoring and managing fall armyworm” Mr Littleproud said. “This includes a series of projects that will investigate fall armyworm genetics, pesticide resistance, commercial and native hosts and modelling of seasonal impacts on population dynamics.

In the meantime, the DPI advises landowners to look for egg masses and small larvae. Larvae may be more active at night. Small larvae, and their damage, can easily be overlooked.

The majority of feeding occurs over a period of around three to five days as the final three larval instars (4–6) complete their development. If smaller larvae in the crop are not detected, the defoliation done by these later instars can appear to happen suddenly.

The DPI emphasises early detection is essential. “Regularly check your pastures for signs of damage or loss of productivity,” the website says. “Use a sweep net or sweep a bucket through the grass to dislodge larvae.

"Larvae may be active during the day in thick stands, but more often at night in less dense, or damaged areas. Once all foliage has been removed, fall armyworm will move en masse to a new area.

"In hay production in the USA, it is recommended that control actions be implemented at 2-3 larvae per square foot (~30cm2).

"In Queensland there are no registered insecticides for this insect in pasture situations, but check the Australian Pesticides and Veterinary Medicines Authority (APVMA) for permits.

"Graziers should assess their pastures on a regular basis and determine the abundance and impact of fall armyworm, and other armyworm species. If a loss of production seems likely, seek advice on what options are available to limit loss of production.

"A useful non-chemical approach is to heavily stock the infested paddock(s) to utilise the pasture before it is eaten by armyworm, and physically reduce armyworm populations through stock movement.

"The APVMA is assessing, as a priority, applications for permits for the use of chemicals against fall armyworm in pasture.

"Check for the latest chemical permits applying to fall armyworm by using the APVMAs permit portal. Search for 'fall armyworm' and tick the 'pest/purpose' button."

The Consultative Committee on Emergency Plant Pests has determined it is not technically feasible to eradicate fall armyworm from Australia. It has never been eradicated anywhere else in the world.

It moves and reproduces fast and feeds on a very wide range of plants. It is well established in our nearest neighbours and could be continually reintroduced. Fall armyworm is most likely found in warm, moist regions with little forest cover. 

To share the latest information about fall armyworm in Queensland, several webinars have been created and are planned for future months.

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