sustainability through science & innovation

PestFacts Issue No. 11 - 8th October 2015

Grubs everywere... but hang on, they're eating out aphids!

Diamondback moth larvae lurking

Build up of aphids is for some much worse than others

Native budworm populations are patchy, regionally speaking

Etiella moth flights looming

Grubs everywhere… but hang on, they’re eating our aphids! Hoverfly larvae feed on aphids and adult hoverflies are pollinators.These are good grubs, but they are often misidentified as diamondback moth larvae or other pest caterpillars

Hoverfly larva with tapering head region and no visible legs (left) and diamondback moth larva with a defined head capsule and six true legs (right) (Source: cesar) Where have they been reported?

Green legless grubs have been found in sweep net catches within legume and canola crops within the Victorian Wimmera and Mallee, as well as the NSW Riverina. These have been identified as hoverfly larvae, a beneficial insect that feeds on aphids in it’s juvenile stage. They are often found in crops during spring in response to aphids colonising crops. In many instances people misidentify hoverfly larvae as pest grubs, often diamondback moth caterpillars.

About hoverflies

Hoverflies are flies from the family Syrphidae. The adults have large eyes and a flattened body with black and yellow/orange markings; hence they are easily confused with bees. Adults are pollinators; they feed on pollen and nectar. The larvae are maggot-like, legless grubs with a tapering head region and no eyes. Larvae can grow to up to 10 mm long and they vary in colour from cream to green or brown; many have a white stripe down the centre of their back.

For further information on hoverflies and other beneficial insects likely to be encountered in broadacre crops and pastures, view the GRDC Back Pocket Guide – Beneficial Insects (PDF, 2.3MB).

Our advice

It is important that hoverflies are correctly identified before deciding on control strategies. Click here for images of hoverflies. Larvae are a very reliable form of control during the warmer days of spring when low to moderate numbers of aphids are present.

Source of field reports of hoverflies Simon Craig – Agronomist, Agronomise Pty Ltd. (Victorian Mallee) Andrew Reardon – Agronomist, AGnVET (NSW Riverina) John Robertson – Agronomist, Agwise Services Pty Ltd. (Victorian Wimmera) Justin Tidd – Agronomist, Landmark (NSW Riverina) Nick Zordan – Agronomist, Western Ag (Victorian Wimmera)

Diamondback moth larvae lurking DBM populations are smaller and less advanced than this time last year, but in some areas activity is steadily increasing

Diamondback moth larvae and feeding damage (Source: cesar). Where have they been reported?

In Victoria’s western Mallee (Underbool), moderate numbers of diamondback moth (DBM) (Plutella xylostella) caterpillars have begun to appear in canola during the last week of September. Most were quite small and probably below threshold, however, the rapidly warming conditions are expected to boost the development of this generation. In the Mallee, near Ouyen, 1-2 larvae per ten sweeps were observed in canola, but were well below threshold.

About diamondback moths

DBM tend to be most abundant during spring and summer. The moths are active at dusk and throughout the night, but usually do not fly far within a crop. Outside the crop, however, DBM can migrate long distances on prevailing winds, especially when their host plant has died. DBM can significantly impact canola yields and current control measures are variable.

Populations are likely to continue to increase over coming days and weeks now temperatures have increased. DBM development rate is closely linked to temperature; at 28°C, the lifecycle only takes about 14 days. Heavy rain events can cause significant larval mortality by drowning; therefore, we recommend re-assessing spray decisions after any forecast rain.

SARDI Entomologist, Kym Perry, believes the current low numbers are at least partly the result of low populations of DBM in wild hosts in autumn prior to sowing. Approximately 50% of sentinel crops in SA field surveys now contain DBM, but larval populations remain low and well below threshold levels across all districts.

For comprehensive information on DBM in canola crops, including their occurrence, lifecycle, behaviour and management strategies, go to diamondback moth within the new PestNote series.

Thresholds and monitoring

Canola crops can tolerate considerable leaf damage before yield is affected. See GRDC Diamondback moth Fact Sheet for more information. Kym Perry and fellow entomologist, Greg Baker (SARDI) advise that, during flowering, DBM can cause significant yield loss if they feed on flowers within the terminal spike.There are no reliable thresholds for this early stage, but thresholds would probably be lower than the original ones (i.e. less than 30 per 10 sweeps). However, it is worth keeping in mind that the original work on DBM thresholds was undertaken with cheaper broad-spectrum insecticides; the only effective chemical options now available are more expensive, placing downward pressure on thresholds.

Build-up of DBM populations within canola crops is very likely over the next few weeks, however, Kym suggests that crops within 3-4 weeks of harvest are considered at low risk of economic damage from DBM. Therefore, monitoring canola crops fortnightly is likely to be adequate at this stage, but if numbers do approach threshold levels, monitoring frequency should increase to weekly until harvest.

Our advice

Sampling crops at several locations is important to determine whether numbers of DBM are increasing or decreasing before any spray decision is made.

If control is needed, keep in mind that moderate to high levels of resistance is widespread in Australian populations. Avoid pyrethroids and organophosphates, either alone or in mixtures, because they are ineffective for DBM control and will kill beneficial insects, potentially leading to other problems (e.g. DBM or aphid resurgence).

Bacillus thuringiensis products and two new synthetic insecticides, Affirm® and Success Neo®, are registered for DBM control in canola; these are less disruptive to beneficial insects. No single insecticide application will completely eliminate the DBM population. In years when populations are large, a two-spray strategy is recommended within seven days to control DBM. Sources of advise and field reports of diamondback moth

Greg Baker - Researcher, SARDI (South Australia)

Brad Bennett – Agronomist, AGRIvision Consultants (Victorian Mallee)

James Mckee – Grower (Victorian Mallee)

Kym Perry – Researcher, SARDI (South Australia)

Matthew Whitney – Agronomist, Dodgshun Medlin (Victorian Mallee)

Build up of aphids is for some much worse than others The incidence of aphids has been highly variable both among crops and regions. Northern NSW have had reports of virus symptoms in chickpea crops

Cabbage aphids on canola (Source: Phil Bowden)

Where have they been reported?

Aphids appear to be one of the most consistent crop pests this spring, with reports from central and northern NSW and central and southern Victoria. However, the nature of reports differs greatly between regions.

Victoria:

Central and South Western districts:

Generally cereal crops have low numbers of aphids, although there has been an obvious difference between crops that used insecticide seed treatments (having low aphid numbers) and those that did not (having higher aphid numbers). These flow-on effects of seed treatments into spring are related to the size of overwintering colonies, which then build up in early spring. In paddocks where aphid populations are relatively high, there is evidence of parasitoid activity (aphid mummies) as well as hoverfly larvae.

Canola crops across the region generally have low numbers of winged aphids on the edges of crops at present. However, there are few established colonies. In these crops, hoverfly adults have been reported. The same scenario for aphids has been observed in faba bean crops, although brown lacewing adults and parasitoids are the most common beneficials reported. NSW:

Central West Slopes & Plains:

Bluegreen aphids (Acyrthosiphon kondoi) are building up within lucerne crops, as well as on under-sown clover pastures around Condobolin. This comes after cereal aphids have built up and have now declined within the area.

North West Slopes & Plains:

Reports of virus symptoms have been coming from chickpea growers in the Northern region of NSW. These reports, mainly coming from late-sown chickpea crops, correspond with the large influxes of winged aphids (mostly bluegreen and pea aphids (Acyrthosiphon pisum)) that were recorded throughout August.

About aphids

Spring is the time when aphids are most commonly seen, particularly on the upper parts of plants and around the growth points. Where present, natural enemies, including hoverfly larva, lacewings, ladybird beetles and parasitoids, can keep small to moderate populations of bluegreen aphids under control during spring.

For more information about aphids, including their occurrence, lifecycle, behaviour and management strategies, go to bluegreen aphid and pea aphid within the new PestNote series.

Our advice

Growers should remain alert to the risk of aphids causing damage and spreading virus, particularly in late sown crops. Monitor 3-5 locations in the crop and examine 5 plants at each location. Also, watch out for evidence of aphid parasitism (aphid ‘mummies’) and monitor their changing numbers over time. Parasitoids play an important role in suppressing spring populations of aphids and other pests.

Source of field reports of aphids

Frank Henry – Regional Research Agronomist, DEDJTR (Victorian Wimmera)

Neil Hives – IPM consultant covering central, southern and western Victoria (based in Central Victoria)

Joop van Leur – Plant Pathologist, NSW DPI (NSW North West Slopes & Plains)

Olivia Wright – Agronomist, AGnVET Services (NSW Central West Slopes & Plains)

Native budworm populations are patchy, regionally speaking Pheromone trap catches across south-eastern Australia have declined in the last two weeks. Sweep net monitoring of budworm larvae reveal densities ranging from very low to moderately high

Native budworm caterpillar (left) and moth (right) (Source: cesar). Where have they been reported?

In the Victorian Mallee, pheromone trap catches of the native budworm moth (Helicoverpa punctigera) have generally declined over the past two weeks relative to those observed in early-mid September. Trap catches in Victoria’s Wimmera, Northern Country, Central and South West districts, and NSW’s Riverina and Central West Slopes and Plains have also been low, suggesting minimal egg-laying in these areas.

Reports of crop monitoring for native budworm reveal a range of infestation levels of the larval stages. In the Victorian Mallee (Ouyen), many pea crops have budworm larvae at or above threshold and have been sprayed. The larvae ranged in size from 3 to 10 mm and are likely to have arisen from August moth flights. Vetch, with a current value of over $1000/t, is also being sprayed for budworm larvae. Numbers have been low in canola and lupin crops. In the Victorian Wimmera, most pulses have been checked but there are no signs of budworm larvae.

About native budworm

For comprehensive information on native budworm, including their occurrence, lifecycle, behaviour and management strategies, go to Native Budworm within the new PestNote series.

Forecast modelling and budworm growth rates

Our predictive modelling tool (Darabug) uses average temperatures from a range of meteorological stations from which to generate forecasts of budworm development rates. Based on the dates of the latest peak moth catches (albeit very small catches in many cases), the predicted dates for third instars are as below:

Victoria

Central and South West: 11 November

Wimmera: 30 October

Eastern Mallee: 21 October

Northern Country: 01 November

NSW

Riverina: 23 October

Central West Slopes & Plains: 22 October

Third instar larvae are relatively easily seen in sweep nets (3 to 5 mm long) and relatively easily controlled, particularly with biologically active insecticides. Fifth instar larvae, which is the stage in which most seed damage begins, typically appears about a week later.

In cases where predictions were made from very low catches, predicted egg lay dates are less reliable. This is because these moths may have arrived much earlier, or possibly, emerged locally. The majority of moths caught in pheromone traps are expected to be recent immigrants that will typically mate upon arrival and soon after begin egg lay.

Our Advice

The recent hot conditions will have brought flowering of most crops to an end, and should curtail budworm egg- laying. Nonetheless, monitoring crops should begin from early podding, particularly after the predicted date for third instar larvae.

Monitor crops regularly using sweep nets; it is important to sample representative parts of the entire paddock prior before making a control decision. Taking multiples of 10 sweeps within at least five locations in a paddock is recommended. Important note: sudden hot days can drive young caterpillars directly into pods. Economic thresholds for native budworm should be followed. These vary according to crop, control costs and anticipated crop return. Comprehensive and dynamic economic thresholds have been developed for native budworm in pulses/legumes in Western Australia. These should also apply to south-eastern Australia. Table 1 provides an example, assuming cost of control at $10/ha. Control is warranted if the cost of control is less than the value of the yield loss predicted. With the increase in grain prices over the last 12 months, economic thresholds have decreased.

Table 1: Yield loss estimates for five pulses and corresponding economic thresholds (ET) for native budworm

K – Loss for each P – grain price C – cost of control ET – larvae per larva in 10 sweeps ($/tonne) ($/ha) 10 sweeps (kg/ha/larva)

Field peas 50 400 10 0.5

Lentils 60 680 10 0.3

Faba bean 90 500 10 0.2

Chickpeas - desi 30 600 10 0.6

Canola 6 450 10 4.0

Lupins 7 420 10 4.0

Sources of field reports of native budworm

Brad Bennett – Agronomist, AGRIvision Consultants (Victorian Mallee)

Ben Cordes – Agronomist, Tylers Hardware & Rural Supplies (Victorian Wimmera)

Luke Maher – Agronomist, AGRIvision Consultants (Victorian Mallee)

Acknowledgements

We thank the following for providing various forms of support to this forecast service:

Institutional Support • Prof Peter Gregg and Dr Alice del Socorro – School of Environmental & Rural Science, University of New England, Armidale • Bill Kimber and Helen DeGraaf – SARDI • Alex Mills – Adama Australia Pty Ltd

Trap operators/facilitators • Brad Bennett – Consultant, AgriVision (Victorian Mallee) • Jim Cronin – Agronomist, Landmark (NSW Central West Slopes and Plains) • Allan Edis – Agronomist, Landmark (NSW Riverina) • Anna Fry - Trainee Agronomist, SHC (Victorian Mallee) • Bill Gardner – Agronomist and Grower, (Victorian Wimmera) • Shayn Healy – Agronomist, Crop Rite Pty Ltd (Victorian Mallee) • George Hepburn – Agronomist, Tylers Hardware & Rural Supplies (Victorian Wimmera) • Neil Hives – IPM consultant central, southern and western Victoria (based in Central Victoria) • Damian Jones – Irrigated Cropping Council (Victorian Mallee) • Jake Leith – Tech Services Agronomist, AgriVision (Victorian Wimmera) • Rob Sonogan – Consultant, AgriVision (Victorian Mallee) • Greg Toomey – Agronomist, Landmark (Victorian Northern Country) • David & Lachlan Trewick – Growers (Victorian Northern Country) • David White – Agronomist, Delta Agribusiness (NSW Riverina)

Etiella moth flights looming Etiella moth activity is likely to have commenced in northern parts of the Victorian Mallee this week, and in other regions in the next 7-14 days

Etiella moth (left) and caterpillar on damaged pods (right) (Source: SARDI)

Where have they been reported?

The very occasional Etiella moth has been seen in lentil crops in the Victorian Wimmera but no other reports have been received from Victorian or New South Wales. The threshold has been exceeded in several areas of South Australia.

About Etiella

Etiella, also known as the lucerne seed web moth (Etiella behrii), is a sporadic but serious pest of lentils in southern Australia.

For comprehensive information on Etiella that affect lentil crops, including their occurrence, lifecycle, behaviour and management strategies, go to Lucerne seed web moth, within the new PestNote series.

Predicted moth activity

The Etiella degree-day model predicts peak Etiella moth flight periods based on local temperatures. This can be used as a guide for when to commence monitoring.

As of 5th October 2015, cumulative degree-days based on actual temperatures and the approximate threshold date for Etiella flight activity based on 20 years of average temperature data at some lentil cropping areas were:

• Horsham (Vic) – 301 dd (about 14th October) • Swan Hill (Vic) – 351 dd (about 3rd October) • Elmore (Vic) – 252 dd (about 22nd October) and • Wagga Wagga (NSW) – 279 dd (about 17th October). The date when the cumulative total of degree-days (dd) first reaches 351 is the date to commence crop monitoring. The dates are only guides and will depend on temperatures over the next few weeks. Moth activity may occur either side of these dates. Refer to PestFacts Issue No. 10 for further details of the Etiella model and how to use it.

Sources of field reports of Etiella

Ben Cordes – Agronomist, Tylers Hardware & Rural Supplies (Victorian Wimmera)

> In this issue

Grubs everywere... but hang on, they're eating out aphids!

Diamondback moth larvae lurking

Build up of aphids is for some much worse than others

Native budworm populations are patchy, regionally speaking

Etiella moth flights looming

What is PestFacts? PestFacts is a free e-mail service designed to keep growers and farm advisers informed about invertebrate issues – and solutions – as they emerge during the winter growing season. The service has a focus on pests of broad-acre grain crops.

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