Fall armyworm in Western Australia

Management in grains, canola and pulses - 
wheat, barley, oats, canola, pulses

A variety of grain crops are grown in Western Australia across different regions.  In the north, fall armyworm is expected to persist year round, therefore grains grown in those areas are likely to be vulnerable throughout the production period. The potential of fall armyworm to migrate into the southern grain producing areas of Western Australia, such as areas of the Wheatbelt and Great Southern, and damage crops at various growth stages is not yet known. Growers should be vigilant and aware of this new pest when monitoring cereal, canola and pulse crops for pests. 

Cereals, canola and pulses are considered secondary host plant for fall armyworm and may not be attacked if a preferred host plant, such as sorghum or maize, is available. Information about fall armyworm in cereals, canola and pulses can be found below.

Information on the management of fall armyworm on sorghum and maize and sweet corn crops is available on separate webpages.

Cereals, canola and pulses are considered secondary host plants and may not be attacked if a preferred host plant, such as sorghum or maize, is available. Information about fall armyworm in cereals, canola and pulses can be found below.

Damage

Cereals (wheat, barley, oats)

Kansas State University advises:

• The first sign of damage is “window-pane” injury caused by tiny larvae chewing on seedling leaves. 
• The larvae, which are usually too small to be easily observed at this time, hide in or around the base of seedlings. 
• Within a few days, the larvae become large enough to destroy entire leaves. 
• Larvae increase in size at an exponential rate, and so do their food requirements. 
• Later instars do the most damage, sometimes destroying entire stands, and are the least susceptible to insecticides. 
• Without treatment, problems can continue until larvae reach maturity or until a frost kills caterpillars.

Canola and pulses (chickpea, faba bean, field pea, lentil, lupin, mungbean)

For seedlings, tiny larvae produce small window-pane damage to leaves, while larger larvae can cut the base of the plant. Mature plants suffer attack on reproductive parts. Later larval instars make larger holes, causing ragged leaf damage, and produce larger droppings.

Monitoring 

Until we acquire a greater understanding of fall armyworm in southern grain growing regions of Western Australia, it is recommended that growers monitor crops for fall armyworm in a similar way as currently conducted for existing caterpillar pests which are similar in size and cause comparable damage to vegetative and reproductive parts of plants. 

Cereals (wheat, barley, oats)

Current monitoring techniques for existing armyworms include visual inspection for leaf damage and caterpillars at early growth stages and a combination of visual inspection and sweep netting for later growth stages. Thresholds are not well-established for existing armyworms in Western Australia.

For information on the commonly occurring armyworm in cereal crops, see DPIRD’s webpages Diagnosing armyworm and Armyworm: economic considerations for management.

Fall armyworm is most active in the morning or late afternoon and may hide during other times of the day.

Canola

Crops from seedling stage through to bolting should be inspected for leaf-chewing damage caused by caterpillars. Cutworms and weevils may also cause chewing damage.

To monitor fall armyworm in flowering or maturing canola in spring, fall armyworm should be identified and counted via sweep netting programs, which are already occurring for native budworm and diamondback moth caterpillars.

Kansas State University advises:

• Examine plants along the field margin as well as in the interior because fall armyworm often moves in from road ditches and weedy areas. 
• Look for windowpane damage in young canola plants or cut plants. 
• Do not allow fall armyworms and cutworms to reduce plant numbers at the seedling stage.

Pulses (chickpea, faba bean, field pea, lentil, lupin, mungbean)

Crops from seedling stage through to bolting should be inspected for leaf chewing damage caused by caterpillars. Cutworms and weevils may also cause chewing damage.

To monitor fall armyworm in flowering or maturing pulse crops in spring, fall armyworm should be identified and counted in sweep netting programs, which are already occurring for native budworm caterpillars, which look very similar.

When to take action

Cereals (wheat, barley, oats)

Thresholds for fall armyworm in cereals are not well-established. The common armyworms, which are known to cause damage to cereal crops in Western Australia, especially maturing barley, may pose a greater risk than fall armyworm, however growers should be vigilant and monitor for fall armyworm in their crops.

Kansas State University advises that if 25-30% of wheat plants have feeding damage, watch closely and apply a control if plant stands are threatened.

Fall armyworm feeding on a wheat plant in Kansas, United States. Photo credit, Holly Schwarting, K-State Research and Extension

Canola

Thresholds for fall armyworm in canola are not well-established. Applying the threshold calculations for native budworm may assist in providing optimal management of fall armyworm

Kansas State University advises:

• Economic thresholds are not well established in canola, but damage is usually minor and yield loss minimal if the plants are healthy and growing vigorously and populations are not excessive. 
• Producers should watch fields closely and only treat if larval populations appear to threaten stands, cause significant defoliation or begin feeding on seed pods.

Management 

An integrated pest management (IPM) approach should be considered for protecting crops from infestations of fall armyworm. 

Fall armyworm has entered an existing suite of pests and associated natural enemies, systems of production and pest management programs.  Careful consideration needs to be given to any actions taken for fall armyworm control that may have adverse effects on management options already in place for other pests in grains crops, especially where natural control agents are used. 

Natural enemies of other insects in the same group as fall armyworms that are already present in grains crops may also attack fall armyworm. There is already evidence of wasps parasitising fall armyworms in maize and sorghum in Kununurra. However, the effect of natural enemies with fall armyworm will become more clear as our experience with the pest accumulates. 

An important management practice is to maintain farm biosecurity measures and implement good farm hygiene, and remove alternative hosts such as weeds and volunteer crop plants, especially during periods, and in places, where fall armyworm would not easily be able to survive year-round. 

Other cultural practices, such as trap cropping, may reduce fall armyworm numbers. Understanding the value of the various cultural practices for fall armyworm management that have been tested overseas will require further study under Australian conditions.

In the short term, insecticides are available to help protect crops from fall armyworm. However, this insect has a reputation for developing resistance to insecticides. Resistance management strategies will therefore be required to maintain the effectiveness of insecticides for controlling this pest.

Application of insecticide will be most effective if applied late in the day and into the night, when larvae become more active and emerge from protected areas of the plant.

Insecticides available for use against fall armyworm includes those available under recently approved Australian Pesticides and Veterinary Medicines Authority (APVMA) minor use permits. Also available for use in WA, are any insecticides registered for use on crops for control of other insects if those products are considered effective on fall armyworm and provided they are applied according to label details. See section 87 ‘Use in accordance with label’, page 53 of WA Health (Pesticides) Regulations 2011. 

The following tables list the details of pesticides available with current permits in Australia for winter cereals (Table 1), canola (Table 2) and pulses (Table 3), and their specified application rates. Permits for other grains are also available. The permits should be read in conjunction with the relevant product label for information on withholding periods and other critical comments.  

More detail on the permits is available from the information sheets found on the APVMA Portal. A direct link to each minor use permit PDF is provided in the tables below. 

Note: New permits are regularly issued for fall armyworm control. Check the APVMA Portal for the most current information. 

Table 1. List of current permits in Australia for winter cereals (as at 20 May 2020)

*Insecticide Resistance Action Committee  **Mode of Action

Table 2. List of current permits in Australia for canola (as at 20 May 2020)

*Insecticide Resistance Action Committee  **Mode of Action

Table 3. List of current permits in Australia for pulses (refer to permits for pulse types)

*Insecticide Resistance Action Committee  **Mode of Action

For a list of registered insecticides for cereals, canola and pulse crops in Western Australia, including for other armyworms in cereal crops, see DPIRD PestFax team’s Autumn winter insecticide guide and Winter spring insecticide guide.

For more information on fall armyworm in grain crops visit:

• DPIRD’s PestFax newsletter article on Fall armyworm
• GRDC’s Fall armyworm webpage

Important disclaimer

The Chief Executive Officer of the Department of Primary Industries and Regional Development and the State of Western Australia accept no liability whatsoever by reason of negligence or otherwise arising from the use or release of this information or any part of it.