Release of insect identification guide for pulse industry in the North region

By Kate Charleston | Published: April 3, 2012
The recently published “Good Bug, Bad Bug” insect identification guide will be an invaluable tool for pulse producers in Queensland and NSW. The new guide features over 300 glossy photos of insects found in pulse crops and will help growers and their advisers to confidently identify the pest and beneficial insects that occur in their crops.

Hugh Brier, DEEDI Senior Entomologist and author of the book says what makes this publication so special is that all pulse pests and beneficials are featured in one book.

Hugh Brier in a crop of soybeans with the ‘Good Bug, Bad Bug’ guide

 

The layout also ensures that users can quickly find what they are looking for. Similar looking insects – good and bad – can be found on the same or adjacent pages which allows for a rapid comparison and identification of insects. Images are colour coded so that pests and their natural enemies are easily distinguished. All photographs contain a brief summary of the insect’s status as pest or beneficial and their key characteristics. See below an example of a page from the guide.

This 44 page guide is ideal to take out in the field. Along with the identification information there are sections on integrated pest management, crop sampling techniques and insect pest thresholds for the different pulse crops.

Most photographs in the guide are the work of veteran insect photographer, Joe Wessels – long-time research assistant with entomology at DEEDI in Kingaroy.
Publication of the guide was funded by industry and has been enthusiastically received by pulse crop growers, agronomists and consultants from North Queensland to New South Wales.
You can obtain a copy of the guide from Hugh Brier or Kate Charleston – our details are listed in the DEEDI entomology contacts page at the top of the screen. You can also obtain a PDF copy of the guide (2.5 MB) using the link below. 

 

Good Bug Bad Bug Guide
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Soybean Loopers defoliating sunflower crops

By admin | Published: March 23, 2012

Over the past couple of weeks there have been numerous reports of sunflower crops being defoliated by caterpillars.  

 

The caterpillar has been identified as the soybean looper, and is the same species reported on a couple of weeks ago defoliating soybeans. There are two colour forms of the soybean looper (see pictures below). Although the colour differs, they are both the same species and behave the same way.

 

Soybean looper. Light phase (left) and dark phase (right).
 

Distinguishing loopers from Helicoverpa

The way the larvae move is an important clue. Loopers loop – as they move along they draw their rear legs right up to the front, resulting in the body forming a loop.

Examining the larvae closely, you can see than loopers have 3 pairs of small true legs at the front, then a big gap without legs, and then 2 pairs of ventral prolegs at the rear (not counting the anal prolegs at the very rear of the larva).

 

Helicoverpa in contrast move without raising their bodies far above the leaf, rather they move with a “slink”. Helicoverpa larvae have 3 pairs of small true legs at the front, and 4 pairs of ventral prolegs at the rear.

 

Watch the videos of looper and Helicoverpa 

 

When is control warranted?

There is no local trial data on looper damage to sunflowers or looper thresholds because severe looper infestations occur so rarely.

 

In the US, looper control in sunflower is recommended if defoliation reaches 25% of leaf area, and larvae are still small and the crop flowering or grain filling. When defoliation exceeds 50% yield losses were incurred.

 

The following is useful in making decisions:

·        Yield loss will occur if the top third of leaves is not retained through budding and grain fill (powdery mildew data)

·        One assessment of Helicoverpa defoliation of sunflowers (D. Murray, 1985) showed that 20% defoliation did not result in yield loss

·        Loopers will consume 80% of their total food intake in the final 2 instars before pupating. Consequently, the rate of defoliation will speed up as larvae reach maturity.

·        Loopers do not feed on the buds or developing heads in sunflower

·        Large larvae (25-40 mm) will be close to maturity and likely to stop feeding and pupate within a few days.

 

 

If control is warranted

Loopers are susceptible to Bt (Dipel®) up to about 15 mm in length. If the bulk of the population is larger than 15 mm long, Bt may not control the population effectively, particularly where there is heavy pressure (e.g. ≥ 20 larvae /m2).  However as up to at least 20% defoliation can be tolerated with no yield loss, there is no need to achieve near perfect control to protect crop yield.

 

Deltamethrin is the only other registered insecticide for looper control in sunflower.

 

Loopers will not be controlled by NPV (Vivus Max®) as it is only active against Helicoverpa. Check larvae on leaves and on the heads to see if there are Helicoverpa present. Helicoverpa only require control if there are more than 20 larvae per head.

 

Good coverage is important, particularly as the loopers are likely to be concentrated on the undersides of leaves.

 

 

Monitoring loopers in the crop

 

Look for looper larvae under the leaves. Small holes can be indicative of early looper activity. Turn leaves over gently and watch for larvae dropping off the leaves as they are disturbed.As the crop is progressively defoliated loopers will be more visible in the canopy.

 

Once loopers have been detected in a field the frequency of monitoring may need to increase. The rate of defoliation can increase rapidly over a period of 2-3 days as the loopers become medium and large. It is estimated that a caterpillar larva will eat 80% of its lifetime consumption in the final two instars (last week or so of development). So you can see how a crop can go from a little defoliation to a lot in a week.

 

Sometimes defoliation can happen suddenly as large looper larvae move from weeds in the field where eggs were laid and small larvae developed onto the sunflower plants. Typically this happens as the weeds are defoliated and the larvae look for other sources of food.

 

 

 

 

Other insect pests to consider in making decisions

 

Rutherglen bug, unless in high numbers (more than 30 in a budding crop) do not warrant control. From mid March, Rutherglen bug do not reproduce in sunflower so the risk of populations building and damaging developing seed is low.

 

Helicoverpa larvae will only cause damage to sunflowers at very high densities (more than 20 per head). Helicoverpa larvae will damage developing buds and heads by chewing stems, bracts, florets and developing seed. Often more damaging is feeding damage on the back of heads that allows the entry of head rots.

 

 
Article by Melina Miles
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Loopers out in force in soybeans

By admin | Published: March 7, 2012

High soybean looper (Thysanoplusia orichalcea) populations (20-40/m2) have been reported in many regions in flowering and podding soybeans. While soybeans can tolerate 33% defoliation with no yield loss during the vegetative stages, their defoliation tolerance slips to 16% during podset/early podfill. Consequently, consider taking action if high looper populations are threatening your crop.


Large soybean looper (38 mm). Note the tapered body (towards the head) and 2 pairs of ventral prolegs.

The preferred IPM option, where loopers are the sole caterpillar in the crop, is a Bt-based biopesticide such as Dipel (1-1.5L/ha) or BioCrystal (0.5-0.75L/ha), both with an amino feed adjuvant at 1L/ha.

Biopesticides such as Bt are best applied in the early morning or evening to minimise their breakdown due to ULV. If you are experiencing very heavy early morning dew, then evening spraying is preferable. Note that for ingestion products such as Dipel, good spray coverage is critical. This also applies to helicoverpa virus products such as Vivus and Gemstar (which have zero impact on loopers), and indoxacarb (which is very effective against loopers).


Small looper larva (10 mm) and typical early damage leaf windowing symptomatic of early damage


Using a selective option such as Bt preserves predatory insects in the crop and reduces the risk of flaring helicoverpa. In flowering crops in particular, the use of Bt against loopers gives growers the option of keeping the moderately-selective indoxacarb (Steward®) option in reserve, should above-threshold populations of the more-difficult-to control helicoverpa make an appearance.

Article by Hugh Brier

 
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Bean podborer harassing mungbeans

By admin | Published: March 7, 2012

Damaging bean podborer (Maruca vitrata) populations of up to 100+ larvae/m2 have been observed in flowering and podding mungbeans in the South Burnett, Dawson Callide and Central Highlands. Although podborer is not an uncommon pest in these regions during wet summers, very high populations can inflict devastating damage with zero pod set observed in some crops where the pest is uncontrolled. In wetter seasons, the pest has also been reported on the Darling Downs, albeit usually in lower numbers. Other crops at risk from podborer attack are adzuki beans, navy beans and pigeon pea.


Typical bean podborer damage to flowering mungbeans. Note the webbing surrounding the damaged buds and flowers.

Damage

Early warning signs are large numbers of the distinctive moths flying in the crop. As the moths are flighty and often difficult to see when at rest, consider using a sweep net to catch them and to confirm the species. Flowers and buds that are webbed together are often the first visible sign of larval damage. However flowers infested with small larvae (<5 mm) may show no visible signs of damage until they are cut open. After initially feeding inside the flowers, larvae move to adjacent pods. Larvae are a pale translucent cream with rows of distinctive black spots.


Bean podborer moth Maruca vitrata in typical pose with body raised at front and wings outstretched. (25 mm wingspan).  

Thresholds

The current threshold is a nominal 3 larvae per square metre (based on experience, not research trials However, sampling for the pest is problematic as beat sheet sampling can underestimate bean pod borer populations by a factor of 5. Because sampling is so difficult, the proposed threshold is probably very conservative (erring on the side of caution).
 

Monitoring for podborer

The most reliable way to estimate podborer numbers is to:
1)      determine the number of infested flowering racemes on 10-20 individual plants from different areas of the field. Often the damage is obvious, webbed buds/flowers, but open un-webbed flowers to check for small larvae.

2)      Then multiply the mean number of infested racemes per plant by the number of plants per square metre, assuming one larva per infested raceme.

 

 Many severely infested crops found by Entomologist Hugh Brier have populations up to 50 times the current nominal threshold.


Management

Bean podborer can be controlled with the registered pesticide methomyl®, but where there is sustained podborer pressure, repeated sprays are often necessary. Podborers are also (co-incidentally) controlled by indoxacarb (Steward®) sprays targeting helicoverpa. However, recent DEEDI trials and in-crop inspections show the synthetic pyrethroids (deltamethrin* and alpha-cypermethrin* do not control bean podborer (*registered in mungbeans against green vegetable bug (GVB), and GVB and small helicoverpa respectively). This is despite previous trials (in the 1990’s) showing good podborer control with synthetic pyrethroids.

 
Note the key to managing this pest is controlling early before larvae enter the pods.
 
Podborer can attack as soon as the first early buds appear but infections are typically most obvious at full flowering.  Hugh Brier is keen for any feedback regarding the success or otherwise of podborer control in crops, and also the location of significant outbreaks.
 
DEEDI entomologists are currently evaluating new generation pesticides for podborer and helicoverpa control in pulse crops. These trials aim to identify new pesticides with (a) greater efficacy, (b) a longer period of crop protection, and (c) less impact on beneficial insects than pesticides currently registered in mungbeans. The latter is important as trial data also suggest that more-selective pesticides significantly reduce the risk of flaring helicoverpa. Results to date are promising.
 
Funding for this project comes from the GRDC Northern Grains IPM project DAQ00153
 
Article by Hugh Brier
 
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Collecting to assess Silverleaf Whitefly susceptibility to insecticides

By Melina Miles | Published: March 1, 2012

As the cotton season draws to a close it is time to for the DEEDI team working on Silverleaf whitefly (SLW) resistance monitoring to start making collections of whitefly from across the cotton-growing regions.

Even if SLW numbers are below threshold, it is possible for the team to make collections of either nymphs (on leaves) or adults (using the suction machine). We are currently looking for fields with SLW in any of the cotton-growing valleys to include in the screening for insecticide resistance.

 

Because the cotton industry is so reliant on 1-2 insecticides to control SLW, it is important that the any changes in the susceptibility of the populations be detected early. Every season since 2008, DEEDI has been screening SLW populations in laboratory bioassays to determine if there is any evidence of resistance developing to pyriproxyfen (Admiral®), diafenthiuron (Pegasus ®) bifenthrin (Talstar®), and more recently spirotetramat (Movento®).

 

To date, there has been no change detected in the susceptibility of SLW field populations from cotton-growing regions.

 

Watch the video to see how the field sampling is done and get a glimpse of a bioassay underway in the lab.     

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Managing Silverleaf Whitefly (SLW) – Wet conditions, late crops and immigrant populations

By admin | Published: March 1, 2012

 

Management of whitefly this season will be challenging as a result of the high rainfall and flooding in November and  again in February which has resulted in a wide spread of crop maturity both between and within each region. While some cotton crops will mature on time, others could be set back by as much as six weeks by the cool overcast and wet conditions.

 

Whitefly numbers increased in most cotton growing regions during February although infestations reported vary greatly from zero to 80% of leaves infested. The recent warm temperatures will likely lead to an increase of whitefly numbers in crops as well as through migration.  Whitefly that migrate into cotton crops come from hosts sustained by regular rainfall but which are now becoming less palatable to whitefly.

 

So given the weather conditions, crop maturity and increasing whitefly numbers – how do we manage SLW? The following scenarios illustrate how SLW may be managed in a range of situations.

 

When crops are on time

The threshold matrix (below) should be used to guide whitefly management decisions for crops that are on time, or close to it. This matrix provides an excellent measure of projected population build up and action thresholds for crops that are on time and not subject to mass SLW migrations from surrounding areas. The day degree calculator found at http://CottASSIST.cottoncrc.org.au helps to assess whether crops are maturing on time. The 2011/12 Cotton Pest Management Guide (p 26-28) provides control recommendations using the threshold matrix.

 


 

When crops are late

Whitefly populations in late crops are likely to be a combination of resident and immigrating whitefly. In this situation, the threshold matrix may not be accurate.  as the matrix is based primarily on SLW populations building up in crop without migratory influxes. In addition, the day-degrees that a crop accumulates may no longer align well with the matrix due to flood damage or waterlogging. 

 A crop manager faced with this scenario should aim to avoid honey dew contamination of open bolls. This means that prior to open bolls, influxes of whitefly can be tolerated.


 Delay treatment?

The delay of treatment on late crops may mean that cooler temperature in March/April slows whitefly activity and honeydew production. It also allows more settling time for migratory whiteflies before treatment is applied. Treating too early maybe partially ineffective because of further crop re-invasion by adult whitefly as the treatments efficacy declines. Treating too early increases the risk of having to retreat.

 

Control decisions for late crops and/or where there are influxes of SLW, should be based on:

·         Origin (e.g. local build-up or mass immigration) and numbers of SLW

·         Presence of open bolls

·         Expected time until defoliation leaf drop

·         The rate and level of honey dew accumulation on the crop canopy and lint

·         The likely efficacy and residual impact of the chosen insecticide.

·         Relevant product withholding periods (WHP’s).

Product choices for SLW are primarily limited to knockdowns such as Pegasus (Diafenthiuron) and Pyrethroids (Bifenthrin) or the slower acting IGR’s such as Admiral (Pyrproxifen) and Movento (Spirotetramat). Resistance is a threat to these products, so follow the IRMS. Admiral can only be applied once.  

Late crops with low SLW numbers

Crops with very low whitefly populations, <10% infested, and little honeydew at boll opening should not require control. However numbers and honeydew should continue to be monitored and if there is a sudden increase in whitefly, due to an influx from neighbouring fields, control with a knockdown may be warranted

 

Late crops with moderate to high SLW

If numbers are moderate to high and defoliated leaf drop is 3 or more weeks away an IGR may be the best control option. Pyrproxifen has excellent residual and will mostly prevent the continued build up of resident and immigrant SLW. The Central Queensland experience strongly suggests that Pyriproxyfen (Admiral®) works even better at lower autumn temperatures than it does in summer and is capable of cleaning up dense whitefly populations on late cotton effectively with a single application. Continue to monitor whitefly numbers and honeydew and if adult numbers begin to rebuild – a knockdown may be required.

 

Crops less than 2 weeks from defoliation

If the crop is less than 2 weeks from defoliation and an influx of adult SLW occurs, a knockdown type product may provide better value, keeping in mind relevant WHP’s. Continue monitoring of honeydew and if whitefly numbers start to recover and cause honeydew close to defoliation – consider defoliating a few days earlier. Once defoliant is applied adult whitefly will generally leave the crop and falling leaves will take the nymphs with them.

 

Monitor for honeydew

It is difficult to determine at exactly what point, levels may become problematic once bolls begin to open. In CQ and during later outbreaks on the Darling Downs, honeydew was considered problematic when leaves on the lower canopy became heavily speckled with honeydew. If the leaves are at or get beyond this level and develop a honeydew “sheen” then corrective action is required immediately.

 

Other considerations

Some crops will have an earlier and later maturing phase of bolls. It is important to manage whitefly to reduce the risk of contamination of the earlier bolls. The basic strategies outlined above should be used in relation to the earlier bolls eg, delaying the first treatment as late as possible, but not later than 5% open bolls. However, with ongoing monitoring of whitefly and honeydew as a guide, a second application of an insecticide from a different group may be required. Earlier defoliation may also be beneficial.

 

If, despite efforts to manage whitefly, crops end up with significant honeydew contamination – e.g. lower bolls dark with sooty moulds – then picking should be delayed as long as possible to expose the lint to maximum weathering, especially rainfall, which will help reduce honeydew levels. The long range forecast indicates a high probability of rainfall late February and at various intervals throughout March. In general however, the costs of preventing the problem will be far less than the potential grade penalties for weathered lint – so proactive management is the best option.

 

 Article by Ian Taylor, Richard Sequeira, Paul Grundy and Lewis Wilson.

This article first appeared in the Namoi Valley Cotton tales

 

 

 

 

 

 

 

 

 

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Green vegetable bug (GVB) in late cotton

By admin | Published: February 24, 2012
There have been several reports of GVB occurring in late cotton crops. This has led to some confusion in the industry as to whether GVB needs to be controlled at this late stage in cotton.  Research done by DEEDI entomologists has shown that younger bolls are more susceptible to lint damage caused by GVB feeding. These factors need to be considered when making management decisions regarding the control of GVB.
 
When are bolls susceptible to GVB damage?

Bolls aged 20 days and over (these bolls are hard and about ¾ inches in size) do not incur significant lint damage (brown coloured lint or tight lock) even if fed on by GVB. This means that even if GVB are present in the field, if the  youngest bolls are older than 20 days GVB control is not warranted.

 Bolls younger than 7 days may shed as a result of feeding by GVB.    
          

Thresholds for GVB

Action thresholds for GVB in cotton are

  • 1 bug per metre when sampling with a beatsheet
  • 0.5 bug per metre for visual sampling     

Parasitism by Trichopoda – do parasitised GVB cause any damage?

Research shows that a GVB parasitised by Trichopoda can continue to cause damage for up to 2 weeks after being parasitised.

Trichopoda giacomelli is an important natural enemy of GVB. This fly parasitises mainly adult GVB and in some cases late instar nymphs. Female Trichopoda lay eggs on GVB and when the larvae hatch, they burrow into the bug and feed on its internal organs and body fluids. Within 2 weeks, final-instar Trichopoda larva emerges from the GVB and pupates in the soil.

Although Trichopoda does not kill the GVB immediately and damage can still occur, they do contribute to GVB mortality and help reduce the size of following GVB generations, potentially reducing the risk offuture damage.

              Parasitised GVB adult           

 Which life stage of GVB causes maximum damage?

Late instars nymphs (4th and 5th instars) cause similar damage as the adults.   However third instars will cause about half the damage as an adult while  1st and 2nd instars cause up to one third the damage.

 

 Other factors to consider when controlling GVB in late cotton

Good spray coverage is a prerequisite to successful management of GVB. Unfortunately there are no selective insecticides available for the control of GVB. Hence any chemical used to control GVB will disrupt populations of beneficial insects. This is an important consideration especially when silverleaf whitely or aphids are also present in the field. Disrupting the natural enemies of these pests can lead to bigger problems such as lint contamination.
 
Article by Moazzem Khan
 
 
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Broad mites in cotton

By admin | Published: February 16, 2012
Broad mites have shown up in cotton crops in Emerald and in the Gwydir this season. Whilst the mites themselves are extremely small and difficult to see, even with a handlens, being familiar with symptoms of broad mite infestation may assist with a diagnosis. Read More »
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Watch out for the Blues

By admin | Published: January 25, 2012

  Noticeable numbers of grass blue butterfly larvae (Zizina labradus) have been observed in young soybean crops in the Wide Bay Burnett. While the small green larvae (maximum length 10 mm) may be difficult to see in the crops, the damage they cause is very obvious.

Grass blue butterfly larvae feeding results in windowing of the leaves (this is mostly cosmetic) and destruction of vegetative terminals. Read More »

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Beware of Apple Dimpling bugs

By admin | Published: December 9, 2011

 

There have been several reports of high numbers of apple dimpling bug (ADB) in early squaring cotton throughout the major cotton growing valleys. Also known as the yellow mirid, ADB adults (about 3mm long) are about one third the size of green mirid adults.  They are yellow-green, have dark spines on the legs and hairy wings that are folded flat on the back. Apple dimpling bugs are capable of moving quickly and have a distinctive apple smell when squashed. Read More »

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