Be on the lookout for caterpillar pests and use the guide below to help with identification. Correct identification is important in management and timing of insecticide application.

Common Armyworm Leucania convecta
Common armyworm is generally considered a spring pest but heavy infestations have been recorded in oats in the Jondaryan area. At this time of year common armyworm can defoliate seedling crops and pasture when in high numbers. In spring, as winter cereals are maturing, infestations of armyworm arise from large migrations of moths from inland Australia. Infestations now do not mean that these fields or farms will necessarily get armyworm in spring.

Common armyworm is a hairless, striped caterpillar with three bands immediately behind the caterpillar head. They are nocturnal, hiding under plants during the day and are often observed curled up in a ‘C’ shape. Colour is not a useful identifier for armyworm as it is highly variable depending on diet and population levels, but the three white bands immediately behind the head are always present.

Pupa of the wasp parasitoid Cotesia sp. are present in high numbers and will be an important natural enemy for this pest.

Common armyworm is nocturnal so any insecticide should be applied at dusk/night.  Small (early instar) armyworms can be controlled with Bt which will also preserve natural enemies but it is not effective on large caterpillars. Large caterpillars can be treated with a range of chemicals including chlorpyrifos. More chemical options can be found on http://services.apvma.gov.au/PubcrisWebClient/welcome.do

Be careful if treating infested pastures as there are long withholding periods for cattle grazed on this pasture with reference to export slaughter intervals and export grazing intervals. These intervals are not always marked on insecticide labels.

The export slaughter interval for chlorpyrifos is 42 days and the export grazing interval is 56 days. For  information about slaugher and grazing intervals relating to other chemicals, please contact us via the blog. 

Sorghum Head Caterpillar Cryptoblabes adoceta
Sorghum head caterpillar has been reported in the Chinchilla area in sorghum. Sorghum head caterpillar is a grain feeder with most severe damage occurring at the soft dough stage.

The most obvious identifier of sorghum head caterpillar is webbing in the grain. Caterpillars are similar in appearance to common armyworm but smaller, reaching a maximum size of about 13mm long. Sorghum head caterpillar does not have the three white bands immediately behind the head, and its body is tapered at both head and tail end.

Webbing can make it difficult to get good contact with the larvae when treating infestations with insecticide.

Please refer to the following DEEDI link for more information http://www.dpi.qld.gov.au/26_13758.htm

Castor Oil Looper Achaea janata
Castor oil looper infestations have been reported across the Downs http://thebeatsheet.com.au/general/castor-oil-looper-outbreak/ . Castor oil looper is a pest of broadleaf crops like soybean although most outbreaks in the past few weeks have been in pastures where caterpillars are feeding on broadleaf weeds like pig weed and marshmallow weed.

Castor oil looper is identifiable by a dark band running across its back. It is highly variable in colour and may be striated with various colours including red, pink and black.

Insecticidal control is best targeted at small grubs however outbreaks of castor oil looper are relatively uncommon in crops. They could potentially create a dilemma in pigeon pea refuges as Bt products (e.g. Dipel) can not be used in a Bollgard® cotton refuge.

Article by Zara Ludgate

For information on armyworm identification see previous Beatsheet postings on armyworms.
http://thebeatsheet-ipmnews.blogspot.com/2007/10/can-you-confidently-identify-armyworm.html

http://thebeatsheet-ipmnews.blogspot.com/2007/09/watch-for-armyworms-in-barley-and-oats.html

There is no reason to expect armyworm to behave differently in wheat to barley. This means you can expect to see feeding on leaves whilst the crop is still green, and then on stems as the crop dries down further.

Characteristic armyworm damage in winter cereals
During the vegetative growth phase, plants can tolerate considerable leaf feeding. Leaves may look tattered from the eaten-out leaf margins. Faecal pellets around the base of plants are another indication of armyworm infestation. Armyworm generally do not require control during the vegetative stage.

Ragged flag and other leaves on a maturing barley crop

The most serious armyworm damage in cereal crops occurs when larvae feed on the upper flag leaf and stem node as the crop matures. Larvae target the stem node as the leaves become dry and unpalatable, and the stem is often the last part of the plant to dry. Head cutting begins at this time.

 
 
Head cutting in barley caused by armyworm

Calculating an economic threshold
The following table shows the value of yield loss incurred by 1 larva/square m per day, based on approximate current values for wheat and an estimated loss of 70 kg/ha per larva.

Based on these figures, and the relatively low cost of controlling armyworm, populations in ripening crops in excess of 1 large larva per square metre will warrant spraying.

Monitoring and management strategy
For insecticide application to be economic, check or scout the crop and assess the problem before head cutting starts. Check for larvae on the plant and in the soil litter under the plant. Late in the day, when the larvae are becoming active, use a sweep net (or swing a bucket through the crop) to make a quick assessment of whether armyworm larvae are present in the crop. Infestations are often patchy, so check a number of sites across the field.

Some judgements will need to be made about how quickly the larvae will reach damaging size and when this will occur in relation to the crop’s development.For example, if the crop is nearing full maturity/harvest, and the grubs are still small, then there is most likely no need to spray. Small larvae take 8-10 days to reach a size capable of head lopping.The other extreme would be a late crop that is still very green and at early seed fill. In this case, any small larvae present will most likely reach their most damaging size in time to significantly reduce crop yield, and so a spray is more likely to be required.

I you are unable to monitor the crop on a regular (daily) schedule during the critical period of drying down, and armyworm are present, it may be better to spray just in case. This is not the preferred option, but provides peace of mind in a year like this where armyworm are abundant.

Early recognition
It is essential to recognise the problem early and be prepared to spray when economic damage is imminent. A cereal crop can be almost destroyed by armyworm in just a few days. Whilst large larvae do the head lopping, controlling smaller larvae that are still leaf feeding may be more achievable.

Control
Many chemicals will control armyworms. However their effectiveness is often dependent on good penetration into the crop to get contact with the caterpillars. Control may be more difficult in high-yielding thick canopy crops, particularly when larvae are resting under leaf litter at the base of plants. As larvae are most active at night, spraying in the afternoon or evening may produce the best results.

If applying sprays close to harvest, be aware of relevant Withholding Periods. Always read the label.

Biological control agents may be important in some years. These include parasitic flies and wasps, predatory beetles and diseases.

Description and Life History

Damage
During the vegetative growth phase, plants can tolerate considerable leaf feeding. Leaves may look tattered from the eaten-out leaf margins. Faecal pellets around the base of plants are another indication of armyworm infestation. Armyworm generally do not require control during the vegetative stage.

The most serious armyworm damage in cereal crops occurs when larvae feed on the upper flag leaf and stem node as the crop matures. Larvae target the stem node as the leaves become dry and unpalatable, and the stem is often the last part of the plant to dry. Head cutting begins at this time. One large larva can sever up to seven heads of barley a day. One larva a square metre can cause a loss of 70 kg/ha grain per day. A larva takes around 8-10 days to develop through the final, most damaging instars, so the crop is susceptible to maximum damage for this period. The current high value of barley (over $400/tonne) would suggest keeping a close watch on armyworm infestations in maturing crops.

Armyworm populations in ripening crops in excess of 1 large larva per square metre will usually warrant spraying. For insecticide application to be economic, check or scout the crop and assess the problem before head cutting starts. Check for larvae on the plant and in the soil litter under the plant. Late in the day, when the larvae are becoming active, use a sweep net (or swing a bucket through the crop) to make a quick assessment of whether armyworm larvae are present in the crop. Infestations are often patchy, so check a number of sites across the field.

Early recognition
It is essential to recognise the problem early and be prepared to spray when economic damage is imminent. A barley crop can be almost destroyed by armyworm in just a few days. Whilst large larvae do the head lopping, controlling smaller larvae that are still leaf feeding may be more achievable.

Control
Many chemicals will control armyworms. However their effectiveness is often dependent on good penetration into the crop to get contact with the caterpillars. Control may be more difficult in high-yielding thick canopy crops, particularly when larvae are resting under leaf litter at the base of plants. As larvae are most active at night, spraying in the afternoon or evening may produce the best results. If applying sprays close to harvest, be aware of relevant Withholding Periods. Always read the label.

Biological control agents may be important in some years. These include parasitic flies and wasps, predatory beetles and diseases.

Further information:
Common, northern and sugar-cane armyworms in pasture, and winter cereals, maize and sorghum. http://www2.dpi.qld.gov.au/beef/3250.html