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So what’s next? Preparing for pests in spring 2014

Following some notable pest outbreaks in autumn and winter this year, it is time to plan for the pest issues that may arise over the next two months. After such a big year for pests, we can expect to see beneficials having a marked influence. Monitoring is all-important

 

The value of natural enemies

The natural consequence of intense pest activity earlier this season across the southern cropping zone has been the build up of enormous populations of beneficials insects, except in crops previously sprayed with broad-spectrum pesticides. For example, we have received several reports of aphids being kept in check through the activity of minute wasp parasitoids (about 1mm) which cause the aphids to become mummified, and other beetle and fly predators. Similarly, this year’s widespread cutworm infestations have generated exceptional populations of larger parasitoids, appearing in sweep nets and sticky traps as flies and wasps, ranging in size from 2-25 mm. When monitoring crops for the spring pests, we advise that you maintain a watch for, and seek to preserve, the activity of these beneficials. Download the GRDC back pocket guide or click here for further information on beneficial insects.

For early spring monitoring, use a sweep net and plant inspections for the following caterpillar pests to provide a good indication of the risk posed by these migrant pests.

Diamondback moth caterpillars

Diamondback moth (DBM) (Plutella xylostella) caterpillars are typically most abundant during spring and summer. Conditions this year were initially favourable for DBM, although the succession of frosts in some regions may have reduced DBM populations. For example, despite early signs of DBM in canola crops in late June in the Victorian Mallee, numbers have yet to increase and feeding damage remains relatively limited. In South Australia however, DBM have been quite abundant across most districts. These experiences are a reminder to Victorian and NSW growers to closely monitor canola crops for DBM activity over the coming weeks.

As temperatures warm, DBM development increases considerably and they can have significant effects on canola yields. We recommend checking canola crops sown in the vicinity of volunteer canola and weed brassicas for DBM larvae and damage. Spray decisions should be based on whether larval populations pose an immediate threat of yield loss to the crop. Infested crops should be regularly monitored, particularly if conditions become relatively dry or warm (which will favour DBM development). Pay particular attention to damage targeting the tip of young inflorescences. Zoopthora fungal infections will also limit their build-up where wet weather conditions persist. More information on DBM in PestFacts Issue No. 7.

Etiella moths and larvae

Lentil growers should start preparing for potential spring pests, particularly Etiella (Etiella behrii), also known as the lucerne seed web moth. Etiella is a sporadic pest of lentils in southern Australia, which can damage grain and cause yield losses if not controlled. Newly hatched caterpillars bore into immature pods within 24 hours of hatching to begin feeding on developing grain. Once inside the pods, they are protected from insecticide applications so sprays must target adult moths before egg lay commences. Etiella also attack lucerne and occasionally clover, peas and lupins. The Etiella degree-day model predicts the peak Etiella moth flight period based on local temperatures and this can be used as a guide for when to commence monitoring. Click here for information about Etiella and to access the degree-day model.

Armyworms

Armyworms, like native budworm, are the caterpillar form of a migrant moth that arrives and lays its eggs at night, particularly in late winter and early spring. Also like budworm, the extreme rainfall events in the South Australian inland during April 2014 may have provided ideal breeding grounds for armyworms. Heavy cereal canopies are likely to favour armyworms. Barley is most susceptible, but armyworms also attack wheat, oats, triticale and grass pastures. Armyworms are unlikely to cause damage until late in crop maturity, but growers are advised to be aware of early signs of large numbers of young grubs (through sweep netting and foliage inspections) when they are more easily controlled.

Cereal aphids

We have received a few reports of cereal aphids building up to higher densities in cereal crops. For example, in the Birchip area of the Victorian Mallee, aphids are appearing in densities of about 15-20 per tiller in the worst paddocks of both barley (mostly) and wheat crops at the booting to flowering stage. Growers are encouraged to accurately assess aphid numbers within paddocks, and to repeat inspections at regular intervals. Sampling should occur away from paddock edges to ensure an unbiased estimate is obtained. Inspect 10-20 plants at six sites within a paddock, counting the number of aphids on individual tillers rather than whole plants. Repeated sampling will allow growers to understand the rate of change of aphid populations and beneficial insects in their crop. It is this rate of change that is most informative when determining the need to spray.

Spring control of RLEM – Timerite®

In most cases, earth mites will not pose any further problems this season as crops and established pastures will generally be able to outgrow the feeding damage if they are not under prolonged moisture stress. However, early spring is the ideal time to think about potential mite issues for next season. For large infestations of redlegged earth mites (RLEM), spring control of mites may be justified to protect autumn crops. Control can be timed to occur during a short window in spring when mites have ceased laying winter eggs (eggs that must hatch this season) and before they start laying diapause eggs (over-summering eggs that survive until next season). This approach, known as Timerite®, can significantly reduce RLEM numbers the following autumn, but is not as affective against other mites or lucerne flea.

The optimum ‘spring-spray’ dates for RLEM in eastern Australia are mostly between mid-September and mid-October, and are freely available from the Timerite® website. Some examples of the recommended dates are: Swan Hill - 12th Sep, Horsham - 23rd Sep, Bendigo - 28th Sep, Wagga Wagga - 29th Sep, Dubbo - 14th Oct, and Colac - 16th Oct. Omethoate is recommended for Timerite® sprays due to the long residual and to maximise the control of lucerne flea.

Cutworms

Following unusually widespread infestations of cutworms (Agrotis spp.) earlier this year, we do not anticipate continued problems into spring. Most larvae have now pupated and will shortly begin emerging as moths, the Bogong moth, and migrate away in large numbers. Nonetheless, a very late infestation of mature cutworm larvae (45 mm) was reported from a late chickpea crop near Donald in the Victorian Wimmera. The larvae were defoliating large patches of crop and drawing petioles and leaves into cracks and holes under clods.

 

*Sources of field reports

Bruce Adriaans – Agronomist, Landmark (Victorian Wimmera)

Phil Bowden – Agronomist (NSW South West Slopes)

Greg Baker – Entomologist, SARDI (Adelaide)

Rik Maatman – Agronomist, Landmark (Victorian Wimmera)

Andrew McMahen – Agronomist, Landmark (Victorian Mallee)

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