PestFacts WA

Armyworm update

  • Moora
  • Narrogin
An armyworm caterpillar
A common type of armyworm, Mythimna convecta, on barley. Photo courtesy of DPIRD.

David Cameron (Farmanco) has reported finding armyworm caterpillars in cereal crops around the Moora area over the past month. He noted that generally they were only causing low levels of damage.

An armyworm caterpillar
An armyworm caterpillar. Photo courtesy of Trent Butcher (ConsultAg).

Trent Butcher (ConsultAg) reported recently that armyworm have caused considerable damage to an oat crop south of Narrogin. The larvae were large and few could be found indicating that many of them have likely pupated in the soil already after consuming their full larval diet.

Armyworm caterpillars are often unpredictable as the moths migrate and fly into crops at night and lay eggs during winter and spring. The caterpillars are fat and smooth and may be distinguished by the three parallel white stripes on the collar just behind the head.

Growers need to be mindful of correctly distinguishing armyworm caterpillars from the recently introduced fall armyworm caterpillar and from native budworm caterpillars.

Armyworm caterpillars are most damaging in barley crops close to harvest so monitor crops now. When barley crops are maturing in spring, large armyworm caterpillars climb plants and can chew through the stems, causing the heads to fall to the ground. Damage to wheat and oat crops occurs less frequently and is usually minor compared to damage in barley because the stems are thicker and leaf defoliation does not usually result in yield loss.

The economic level for spraying armyworm in mature barley is about three large armyworm grubs per square metre of crop. The threshold for wheat or oats is much higher as only grains are consumed and heads are very rarely dropped. Spray thresholds in these crops are more like 10 grubs per square metre of crop. If applying insecticide be mindful of harvest chemical withholding periods (WHP) and to check chemical labels before spraying.

A number of effective insecticides are registered for the control of armyworm if required (see DPIRD’s 2022 Winter Spring Insecticide Guide).

To read about previous armyworm activity reported this season refer to the 2022 PestFacts WA Issue 13 article Identifying caterpillars in cereal crops.

For further information on armyworm, refer to DPIRD’s Diagnosing armyworm and Management of armyworm in cereal crops pages.

For more information, contact Technical Officer Alan Lord, South Perth on +61 (0)8 9368 3758 or Research Scientist Svetlana Micic, Albany on +61 (0)8 9892 8591.



Article authors: Cindy Webster (DPIRD Narrogin) and Dustin Severtson (DPIRD Northam).

Clean augers, field bins and silos to prevent insects contaminating grain

Grain silos
On farm grain silos. Photo courtesy of Ben White (GRDC).

The Western Australian grain storage industry is focused on gas-tight sealable storage and fumigation to achieve the federally mandated ‘nil tolerance’ for live insects in exports.

Residual pest populations surviving in empty storages during winter will infest new season grain when it is put into the storages. If eradication of these pests is not undertaken, they may undergo selection for resistance as a result of repeated fumigations.

Gas-tight sealable silos are the preferred system of storage and pressure testing silos should be part of the annual maintenance. It is much easier to replace seals and carry out repairs when silos are empty. Inspection and replacement, if necessary, of inlet and outlet seals as well as checking pressure relief oil valves and topping up with light hydraulic oil if needed is recommended.

It is good practice to pressure test sealed silos upon erection, annually and before fumigating with a five-minute half-life pressure test. See the GRDC supported Stored grain information hub website for more details on pressure testing.  

Augers, field bins and silos should be thoroughly cleaned of grain residues and treated with a structural treatment, such as fenitrothion or diatomaceous earth. The ground around storages should be cleared of weeds and rubbish to prevent harbouring insects. Old grain residues should be burned or buried deep.

Be aware of withholding periods if you are treating the inside of an empty silo with a registered insecticide such as fenitrothion, to provide residual control before the grain is loaded.  

Growers are reminded that the insecticide fenitrothion is not registered as a seed treatment. Fenitrothion is a contaminant in exported grain. Growers using Fenitrothion as a structural treatment in the weeks prior to harvest should leave the chemical in place for 2-3 days and then wash it off to prevent contamination of any grain that may come into contact with the sprayed surface.

Diatomaceous earth is the preferred for in-silo structural treatments. Non-chemical products such as diatomaceous earth (e.g., Dryacide) need at least two weeks before loading grain to be effective. Dryacide is a naturally occurring insecticide and will provide good control for at least 12 months. It is a non-toxic, diatomaceous earth product that is recommended as a structural treatment.

Nitrogen can be used on its own or in combination with other fumigants for effective insect control but requires a very high level of sealing on the silo and the silo to be initially purged along with very high levels of silo sealing to maintain an environment free of oxygen.

Phosphine, however, is the cheapest form of insect control at around 40c/tonne but growers need to be sure their silo is a gas-tight sealable silo meeting Australian Standards AS2628-2010.

Phosphine inhalation is very serious and can be fatal. Always read the Safety Data Sheets, always wear protective clothing including chemically resistant gloves and a full-face respirator with a B category cartridge. Inform others (including putting up a phosphine warning sign) when a storage facility is under fumigation.

In order to kill grain pests at all stages of their life cycle (egg, larvae, pupae, adult), growers should refer to the phosphine label instructions regarding dosage, treatment, ventilation and withholding times.

Poor fumigation can result in only adult and larval insects being killed giving the mistaken impression that the fumigation was successful. However, the immature eggs and pupae will not be killed and infestations will likely build up again quickly, selecting for resistant populations.

Fumigating in an unsealed silo or field bin is an off label use, it is not only ineffective, at best killing adults and larvae, it will also lead to strong resistance developing on your farm.

Managing phosphine resistance

Insect populations with weak phosphine resistance have developed in all grain-growing states of Australia largely as a result of poor fumigations. Strong resistance is widespread in the eastern states and has started to take hold in the west, so to help minimise the development of strong resistance to phosphine in WA, use well maintained gas-tight sealable silos.

Detecting phosphine resistant grain pests early will make eradication possible and will protect your income. To arrange a free resistance test for grain pests contact Technical officers Hannah Hughes or Sam Manning, DPIRD stored grain insect group, South Perth on +61 (0)8 9368 3561.

Farmers keeping grain on farm for their own use, with silos that are not sealed can use aeration as an alternative method to keep insects in low numbers.

Aeration cooling is an effective tool which can be used in combination after fumigation for maintaining insect population control. While aeration cooling will not kill insects, it will dramatically reduce reproduction provided aeration fans are used in combination with an aeration controller to selectively push cool dry air through the grain in the silo at a rate of 2-3 litres per second per tonne.


For more information on stored grain management techniques visit;

For more information contact DPIRD Technical officers Hannah Hughes or Sam Manning, South Perth on +61 (0)8 9368 3561 or Ben White, GRDC grain storage extension team WA on 1800 WEEVIL (1800 933 845).



Authors: Dr Oonagh Byrne (DPIRD), Dave Cousins (DPIRD) and Ben White (GRDC).

Flag smut in wheat

  • Wyalkatchem
  • Elabbin
  • Merredin
Flag smut on wheat plants
Flag smut on wheat plants. Photo courtesy of Geoff Thomas (DPIRD).

DPIRD Plant pathologists Jason Bradley and Kylie Chambers recently found flag smut in wheat near Wyalkatchem (GS41) and Elabbin (GS65).

Dani Whyte (Braeleigh Consulting) has seen flag smut in wheat near Merredin.

Flag smut spores on an infected wheat leaf.
Flag smut spores on an infected wheat leaf. Photo courtesy of Geoff Thomas (DPIRD).

Flag smut is a fungal disease that occurs across the WA grainbelt but appears to be more common through the medium to lower rainfall regions of the central, eastern and northern grain production zones. Barley, oats and broad leaf crops are not affected by wheat flag smut.

This disease generally occurs only sporadically, usually following successive plantings of susceptible varieties without use of fungicide seed dressings. To check flag smut resistance ratings of wheat varieties refer to DPIRD’s 2022 Sowing Guide for WA – Wheat. A number of popular varieties grown in WA are Susceptible or worse and are more likely to exhibit higher incidence of disease. At the Elabbin location, unusually high levels of disease arising from soil borne inoculum were evident in experimental plots. Disease ranged from ~10% incidence of infected plants in a moderately susceptible-susceptible variety to >25% in a susceptible-very susceptible variety.

Flag smut infection occurs as the wheat plant germinates and emerges from soil. The fungus grows systemically within the plant and affected plants are often stunted and infected leaves may be curled and distorted with long grey-black streaks of flag smut spores (which rub off easily). Initially, the spore masses are invisible under the leaf surface, but between stem elongation and heading, they break through the surface as distinct, long, raised streaks of sooty black spores on leaves and leaf sheaths. Infected plants can tiller excessively, but symptoms do not always occur on all tillers. Flag smut differs from other cereal smut diseases by exhibiting symptoms in the leaves/leaf sheaths rather than the heads. Occasionally stems can also be infected.

Flag smut is quite common at trace levels in wheat crops, however at higher incidence it can reduce yield as affected tillers do not usually produce grain.

During harvest, flag smut spores are distributed onto the surface of seed or onto the soil. Spores of the fungus can survive in soil for several years and can be moved to adjacent paddocks by wind, plant debris or equipment. Machinery that has handled contaminated grain should be thoroughly cleaned to avoid contamination of other paddocks/grain.

Seed sown into contaminated soil is at risk of developing the disease as is infected seed sown into clean soil.

Managing this disease next season

Spores of this fungus are carried on seed and in soil, so it is important to consider management strategies now to avoid having significant recurrence of the disease in next season’s wheat crops.

This disease is well-managed by registered fungicide seed dressings, use of more resistant varieties (refer to DPIRD’s 2022 Sowing Guide for WA – Wheat) and rotation with nonhost crops (although spores can last for a period of years in soil).

In paddocks contaminated with flag smut and adjacent paddocks, use clean seed treated with a fungicide seed dressing at a registered (high) rate to reduce disease risk. Registered seed dressings are highly effective. Ensure even, full coverage of grain to maximise protection of all grains sown. Information on which seed dressings are registered for specific diseases is available from DPIRD’s Seed dressing and in-furrow fungicides for cereals page.


Further information is available at DPIRD's Diagnosing flag smut of wheat and Cereal smuts and bunts management pages.

For more information contact Plant pathologists Kithsiri Jayasena, Albany on +61 (0)8 9892 8477, Ciara Beard, Geraldton on +61 (0)8 9956 8504, Geoff Thomas, South Perth on +61 (0)8 9368 3262 or Andrea Hills, Esperance on +61 (0)8 9083 1144. 



Article author: Ciara Beard (DPIRD Geraldton).

Article input: Geoff Thomas (DPIRD South Perth) and Kithsiri Jayasena (DPIRD Albany).


PestFacts WA Reporter app now available for android devices

Mobile phones displaying various screen shots of the new PestFacts WA Reporter app

Growers and consultants with android devices can now download and use the new PestFacts WA Reporter app to make quick reports, or request identifications, of insects and plant diseases from broadacre crop and pasture paddocks anywhere in the WA grainbelt.

The new app that was released in June has recently only been available to apple users.

The PestFacts WA service, which includes the PestFacts WA newsletter and map, relies on your input and observations to alert the WA grains industry of what pests and plant diseases are a threat to WA broadacre crops and pastures.

It is no problem if you are out of mobile range, the app will send your report as soon as it gets a connection. 

This new app replaces the previous PestFax Reporter app, so once the new app is downloaded please delete the PestFax Reporter app.

To download this app visit the Apple app store and Google play store.

For more information refer to DPIRD’s PestFacts WA Reporter app page and explainer video.

For more information contact Senior application developer Steve Collins, Perth on +61 (0)8 9368 3436.



Article authors: Cindy Webster (DPIRD Narrogin) and Steve Collins (DPIRD Perth).