Distinguishing ‘brown’ stink bugs from each other.

 Adults brown stink bugs (Dictyotus caenosus) are shield shaped, matt brown, and smaller than green vegetable bug (GVB), about 7 – 8 mm long (Plate 1). They may be confused with glossy shield bug (Cermatulus nasalis) which is a slightly larger predatory bug, and with rice spotting bug (Eysarcoris distinctus) which is smaller (5 – 6 mm) and has two pale elongated marks on the top (Plate 1). 

  Brown stink bugs lay pale cream eggs in twin row rafts (Plate 2).

Eggs are similar in shape to GVB eggs, but egg rafts of GVB are seldom in two rows. Newly hatched nymphs are orange with dark markings and a black head (Plate 3).  These are indistinguishable from other shield bug nymphs.  As they grow they change colour to have a pale brown abdomen and transverse dark and pale markings at the centre of the abdomen (Plate 3, fourth instar nymphs pictured).

  Mealybugs are small, sucking insects related to aphids. Female adults are around 3 mm long, oval-shaped and covered by a white waxy coating giving them a mealy appearance. Nymphs are smaller but similar in appearance. Males are small aphid-like winged insects.

Mealybugs have a high reproduction rate with female mealybugs capable of producing hundreds of nymphs. Development from egg to adults takes about 26 days and adults can live for about three months.

Damage symptoms

Mealybugs form colonies on shoots, stems, and leaves developing into dense, waxy, white masses. Both adults and nymphs pierce and suck on plant tissue and are able to suck sap from hard tissue, including the main stem and branches. They can affect any stage of crop development.

 Symptoms of mealybug infestations on cotton include; crinkled and twisted leaves, fewer flowers and fewer bolls, smaller bolls, and distorted and stunted plants. Boll opening may also be adversely affected, resulting in serious losses in yield.

Mealybugs, like aphids, excrete copious amounts of honeydew that contribute to the development of a black sooty mould which inhibits the plant’s ability to manufacture its food. Ants feed on the honeydew produced by mealybugs and help to spread the infestation. Ants also protect mealy bugs from predatory ladybird beetles, parasites and other natural enemies.

 Where are they found?

Mealybugs are present in all cotton growing regions of the world. However on the Indian subcontinent, the exotic Phenacoccus solenopsis has become a major pest, possibly due to favourable weather conditions and an abundance of host plants. It has been responsible for heavy losses in Pakistan where it is now considered a major pest of cotton.

A mealybug found in Australian cotton fields in the Burdekin region was identified as Phenacoccus parvus. This pest was introduced accidentally as a contaminant on imported plants in 1988. P. parvus was initially found in isolated populations from far north Queensland to central New South Wales, and around Perth. It is more common in the drier regions of northern New South Wales and southern Queensland and population numbers of P. parvus increase during dry periods. Heavy infestations have been reported on lantana in south east Queensland. The species of mealybug infesting cotton in the Emerald region is yet to be determined.

 Management of mealybugs

There are no registered insecticides for the control of mealybugs on cotton in Australia. In Pakistan numerous pesticides have been evaluated for the control this pest, but a hydrophobic (water repellant) layer around its body makes it difficult to control with insecticides. To achieve effective chemical control, an insecticide must penetrate the outer waxy layer. 

The adult mealybug can shelter in the soil, cracks and other places where insecticide sprays cannot reach it.

The insect damage often appears in patches within a field, along field margins and poorly drained areas.  Mealybugs have numerous weed and crop plants that they use as alternate hosts; cotton, lantana, leucaena and peanuts are just a few.

Control of weeds and ratoon cotton, and avoiding planting on poorly drained soil is the best management option for controlling mealybugs at present.

 More information about the mealybug problem in India and Pakistan can be found on the CRDC website at www.crdc.com.au. To find the article search for mealybugs at the top of the page. 

Other pests

We have received a few reports from other pests in various crops. These include; Rutherglen bugs in mungbeans, monolepta beetles on peanuts and legume web spinners on soybeans. Please let us know if you are finding these pests and we can feature an article on these, or others you find, in the next blog.

Article by Kate Charleston and David Murray. Images by Paul Grundy.

C. Mares (CSIRO)

Just when you thought things were going along pretty well, something else pops out of the woodwork to bring you back down to earth. Some cotton consultants and their grower clients are concerned about the high numbers of thrips in their young cotton seedlings. Are they are problem? Do we need to control them?

Essentially, unless seedling terminals are dying, the damage to leaves, which causes distortion and cupping, is largely cosmetic and in most cases will not compromise yield and maturity. Only extreme populations (70 thrips per plant) caused maturity delays in excess of 7 days. Cool weather can exacerbate thrips damage, while warmer weather will help plants grow away from damage quickly – hence risks are higher in cooler regions and much lower in warmer regions.

Thrips are also important predators of spider mites, feeding on mite eggs as a source of protein, so it is important to weigh their value as predators against potential risk of yield loss or delay.

Which thrips?
Species infesting seedling cotton are tobacco thrips, Thrips tabaci, the most common, and tomato thrips, Frankliniella schultzei. Adults thrips are small, cylindrical insects (<1.5 mm long) with two pairs of narrow wings fringed with long hairs. Thrips tabaci is usually a pale straw colour while F. schultzei is typically almost black. Larvae of both species (< l mm long) are yellow and wingless.

L. Wilson (CSIRO)

The western flower thrips (WFT), Frankiliniella occidentalis is a recent exotic invader also found in cotton regions. It is similar in appearance to F. schultzei but paler, making it easy to distinguish from F. schultzei but hard to distinguish from T. tabaci. WFT causes similar damage to cotton seedlings and also eats mite eggs. It is resistant to a range of insecticides, including many organophosphates and carbamates.

What are we finding?
Most thrips collected last week on cotton seedlings on the Darling Downs were T. tabaci, but low numbers of F. occidentalis were present. The numbers of thrips nymphs were very low, indicating effective control (see below). The presence of high populations of adult T. tabaci where either granular insecticides or seed dressing have been used suggests there are constant influxes of adult thrips moving in from cereals and weeds (see below).

Thrips Thresholds
Due to the capacity to recover from some damage, thresholds for thrips must include both pest abundance and damage levels – which should both be exceeded before control is warranted.

From planting to flowering     (1 flower per metre)
Adults and larvae per plant                10
and
Damage (reduction in leaf area)        80%  (leaves less than 1 cm in length)

Control
Seed dressings can reduce early damage but will degrade over 14 to 21 days post planting (indicted by the presence of thrips larvae). By then leaf area should be sufficient for above-ground applications of systemic insecticides to be effective if necessary. Systemic granular insecticides, applied at planting, provide longer control, but in some districts they are not necessary for thrips control due to low numbers or good growing conditions.

If using seed dressings or granular insecticides be aware that adult thrips will continue to be found in the crop as they move from cereals and weeds. These adults will feed and die, causing no damage. The best indicator of declining control is the presence of thrips larvae which indicates that the pesticide is no longer effective.

For more detailed information on thrips follow this link:

http://www.cottoncrc.org.au/content/Industry/Publications/PestsandBeneficials/CottonInsectPestandBeneficialGuide/Pestsbycommonname/Thrips.aspx

Photo: Downs agronomist Bernie Caffery (right) discusses resistance with Sharon Downes and Grant Herron at the Dalby Resistance Roadshow.

Aphids and mites
Dr Grant Herron, Industry and Investment NSW based at Menangle, presented his latest results for cotton aphids and mites. Cotton aphid resistance to neonicotinoids was detected at many locations during the 2008-09 season and was associated with product failures. Grant suggests that neonicotinoid seed dressings are influencing the development of this resistance. His recommendation is to try to avoid foliar neonicotinoids for aphid control if a neonicotinoid seed dressing has previously been used that season. However, if they are sprayed for aphid control Grant highlighted the need to alternate chemical groups for seed dressing and first foliar spray.

Fortunately there appears to be no cross resistance to pirimicarb, organophosphates and endosulfan and these products should perform satisfactorily against neonicotinoid resistant strains. Cotton aphid resistance to Pegasus® was reported for the first time.

Resistance was detected to Comite® in two spotted mite populations. This is one of the most widely used products for mite control in cotton, so the detection of resistance is a serious concern.

Whitefly
Results of resistance testing for silverleaf whitefly (B biotype) by Zara Ludgate, QPIF Toowoomba, indicate no immediate concerns for the two key products, Admiral® and Pegasus®, used to manage this pest in cotton. Surveys of cropping regions during autumn and winter 2009 have so far failed to reveal any Q biotype Bemisia tabaci that was first reported from north Queensland in late 2008 and north-western NSW in 2009.

Helicoverpa
According to Dr Louise Rossiter, Industry and Investment NSW, Narrabri, resistance in Helicoverpa armigera to most conventional insecticides has declined or stabilised. Areas of concern are the continuing high level of resistance to older pyrethroids and moderate resistance to the carbamates. Field performance of these products against H. armigera may be highly variable. There are no conventional insecticide resistance issues associated with H. punctigera.

The 2009-10 Insecticide Resistance Management Strategy is available on the CRC website:
http://www.cottoncrc.org.au/content/Industry/Publications/Pests_and_Beneficials/Insect_Resistance_Management.aspx

Bt resistance
Dr Sharon Downes, CSIRO Narrabri, and Kristen Knight, Monsanto Australia, outlined the results for resistance testing to the two Bt toxins. While the frequency of Cry 1Ac resistance alleles remains at very low levels, the frequency of Cry 2Ab resistance alleles in populations of H. armigera and H. punctigera are higher than expected. Changes in the frequency of resistance alleles are being closely monitored as further upward movement in resistance frequencies could be a trigger for changes to the Resistance Management Plan which aims to preserve the usefulness of this GM technology.

Photo: Kristen Knight (left) of Monsanto discusses Bt resistance with Kate Charleston of QPIF at the Dalby Resistance Roadshow.

What are the implications?
Overseas studies indicate Q biotype has the capacity to develop resistance to many insecticides including insect growth regulators (IGRs) such as Admiral® and neonicotinoids like Confidor®. High levels of resistance to Admiral® have been detected in horticultural crops in a few locations in north Queensland and some field control problems have been observed for Admiral®.

Resistance testing from cotton production areas for the 2008-09 season has not shown any alarming resistance levels to Admiral® to date.

Overseas where populations are predominately of Q biotype, moderate to high resistance has developed to Admiral®. Where populations were mostly B biotype, Admiral® has retained high efficacy. This has been the case in Queensland where, according to Dr Gunning, B biotype populations remain susceptible to Admiral® and have a higher susceptibility to neonicotinoid insecticides, compared to Q biotype populations. At this stage Q biotype is showing markedly less resistance to pyrethroids than the B biotype.

In Israel, Q biotype has not developed resistance to Pegasus® despite several years of reliance on this product. In horticultural areas, significant resistance to Pegasus® was not found in either biotype.

Integrated Pest Management
Practicing good IPM principles can discourage Q biotype numbers from building up. Under natural conditions, B biotype will out-compete Q biotype. However, in an environment of high insecticide use, the more insecticide resistant Q biotype tends to displace B biotype, and once this shift occurs B may not recover to its former levels. Limiting the amount of chemical used against insect pests may favour the dominance of B over Q.

Q biotype, like B, has the capacity to vector the virus that causes cotton leaf curl disease. This disease is not present in Australia. The main risk is that any new whitefly incursions, whether Q or B biotype, could carry viruses that are not present in Australia.

Identification
Q biotype and B biotype can not be distinguished visually. They can only be distinguished by looking at small differences in their DNA or biochemical make-up.

WE NEED YOUR HELP
In order to determine the distribution of Q biotype, we are asking growers and consultants to send in whitefly specimens to the Queensland Primary Industries and Fisheries, Toowoomba. Please refer to details at the bottom of this article.

FURTHER READING

Whiteflies http://www.dpi.qld.gov.au/cps/rde/dpi/hs.xsl/26_10277_ENA_HTML.htm

The Cotton Industry Biosecurity Plan Appendix 3 provides information on Q biotype (page 32) and Cotton Leaf Curl Virus (page 40).
http://www.planthealthaustralia.com.au/project_documents/uploads/Section%209%20Appendix%203%20Pest%20Risk%20Reviews.pdf

Follow this link to the Fact Sheet on Q biotype whitefly. http://www.dpi.qld.gov.au/cps/rde/dpi/hs.xsl/26_13554_ENA_HTML.htm

WHITEFLY SAMPLING
Adult whiteflies: In fields where whitefly are present, collect a minimum of 30 adults from random plants throughout the crop. Place these in 65% alcohol (watered down methylated spirits) in a leak proof vial or bottle. Note that >70% alcohol is classified as a dangerous liquid and should not be sent via post or courier.

Immatures: In fields where whitefly are present, collect a minimum of 30 leaves from random plants throughout the crop. Aim to collect leaves that have large immature scales (4th instar/red-eye nymphs) on their underside. Collect only 1 leaf/plant. Pack the leaves into a paper bag and then inside a plastic bag.

For live material, send by overnight courier to:
Richard Lloyd
DEEDI, Primary Industries and Fisheries
203 Tor St, Toowoomba Q 4350
Ph: (07) 4688 1315

Ensure samples are clearly labeled and include the following information:
Collectors Name, Phone No., Fax No., Email address
Farm Name, Field, Postcode, Region (e.g. Gwydir)
Date of Collection, Host Plant (Crop)
Comments

Article by Zara Ludgate and David Murray

Green Vegetable Bugs (GVB) in soybeans .

GVB are often found in the crop prior to pod-fill, but at this stage they are not causing economic damage. By delaying insecticide use untill pod-fill reduces the risk of flaring whitefly, because as pod-fill progresses, the leaves become progressively less attractive to this pest.

While many cultivars can compensate for yield loss caused by moderate bug populations, seed quality is adversely affected, particularly for culinary beans which have very low damage tolerances (a maximum of 2% damaged seed). Bug damaged seeds have increased protein content but a shorter storage life (due to increased rancidity). In soybeans, bug damage also reduces seed oil content.

The only effective registered pesticides for pod-suckers are non-selective and include deltamethrin (Decis) and trichlorfon (Dipteryx). Of these, deltamethrin is the most effective. Note that dimethoate and methomyl are also registered but were found to be ineffective against pod-sucking bugs.

To mitigate the impact of non-selective insecticides, delay spraying podsuckers until early podfill.

Green Vegetable Bugs (GVB) in cotton
Cotton is susceptible to damage from GVB from flowering through until one open boll per metre. Damage symptoms from GVB cannot be distinguished from damage done by mirids which include warty growths and brown staining of lint in developing bolls.Thresholds for GVB in cotton are 1 adult/metre from flowering through to harvest. For insecticide options please refer to the cotton pest management guide which can be found on the Cotton Catchment Communities CRC website.

http://www.cottoncrc.org.au/content/Industry/Publications

Grass blue butterfly
Large populations

of grass blue butterfly have been observed in soybeans this season. The green slug-like caterpillars feed mainly on leaves. They may be confused with the larvae of the hoverfly which is a beneficial insect and often found near aphid colonies on which they feed.

While control is rarely needed, high numbers can damage terminals resulting in plant branching and pods being set closer to the ground. This can indirectly impact on yield as low-set pods are more difficult to harvest. There are no insecticides registered for this pest specifically but anecdotal evidence (from a leading Goondiwindi grower) suggests they are readily controlled with Bt (Dipel).

Pale cotton stainers
Cotton stainers are occasional pests of cotton that feed on developing and mature cotton seed. While previously controlled by broad spectrum insecticides for other pests in cotton, the reduction in chemical use, especially on Bollgard II®, may lead to increased populations which may need to be managed.
For more information about pale cotton stainers click on the link provided below:

http://www.cottoncrc.org.au/content/Industry/Publications/Pests_and_Beneficials/Sucking_Pests.aspx

 

 

Article by Kate Charleston and Hugh Brier

It is thought that increased host plant availability from a wet winter/spring, warm conditions and a decline in natural enemies due to the use of broad spectrum insecticides has contributed to the high SLW numbers in this more marginal area of occurrence.

DPI&F entomologists will be visiting Narrabri on Thursday, 11 February 2009 and Moree on Friday 13 February 2009 where they will meet with growers and consultants and speak about SLW and the management options that are available.

Cotton fields around St George are at or reaching high densities of SLW. Reports indicate Admiral® has been applied on many fields to suppress SLW populations. Parasitism levels of 50% and 70% were recorded from two fields in the St George area. This should help to keep SLW in check later in the season even if they start to re-infest crops post Admiral® spray.

SLW numbers in Biloela and Theodore are reportedly dropping off. This may be in part due to parasitism levels. Recent testing for insecticide resistance in populations of SLW from Biloela and Theodore show no alarming results for Admiral®. These results were expected due to the minimal use of Admiral® in central Queensland this season.

GHW are in moderate densities in the Norwin region on the Darling Downs. While GHW will produce honeydew it does not normally cause the same problems as SLW which has a wider host range, higher reproductive rate, develops resistance to insecticides rapidly, and is adapted to high temperatures. Where populations are a mix of SLW and GHW, consider treating as if all are SLW.

The report on managing silverleaf whitefly by Richard Sequeira and Tracey Farrell can be accessed through the cotton CRC using the link below: http://www.cottoncrc.org.au/files/5743fee2-f978-4a79-a9d1-9b1800e899cf/Whitefly_Management[1].pdf.
This document outlines sampling, thresholds and management options for SLW. Remember only one spray of Admiral® is allowed per season.

Article by Zara Ludgate

Resistance testing for the 2007-08 season indicated no alarming results for Admiral® (pyriproxyfen) or Pegasus® (diafenthiuron) in cotton areas. The IRMS guidelines for Admiral® require that only 1 spray may be applied per season. Apart from the cost involved, more then one Admiral® spray has been shown to increase the development of resistance.

As part of the management strategy for whitefly it is important to know what species or biotypes are present as these will significantly impact on the management decision that is required. Refer to past beatsheet articles to read more on identifying the different species and biotypes of whitefly.

We are seeing mixed populations of whitefly across Queensland. On the Darling Downs, greenhouse whitefly (GHW) has made up >90% of the population in the Norwin area. A sample from Theodore showed the whitefly population was made up of 70% SLW and 30% GHW.

In Emerald, a limited number of Pegasus® sprays have been applied for SLW. Pegasus® is best used for early season suppression of SLW at low insect densities or as a late season knock down to prevent honey dew contamination of open bolls.

Very few (if any) Admiral® sprays have been applied so far this season. Admiral® may be applied after 1450 day degrees if SLW numbers reach high densities. Remember that only one Admiral® spray may be applied per season to limit the potential for resistance to develop.

An excellent publication has been produced through the Cotton CRC by Richard Sequeira and Tracey Farrell That outlines thresholds and sampling methods for SLW in cotton in more detail (www.cottoncrc.org.au/files/5743fee2-f978-4a79-a9d1-9b1800e899cf/Whitefly_Management.pdf). This should be referred to when making management decisions for this pest.

In Emerald, there were high levels of natural control of whitefly from the parasitic wasps, Eretmocerus hayati and Encarsia formosa. Parasitism levels of 40% and 75% were recorded in two fields in the Emerald Irrigation Area. In a field at Biloela, parasites were so abundant that the tiny wasps were clearly visible walking around on leaves.

It is likely that the high parasitism levels recorded in Emerald and Biloela are due, in part, to very limited mirid sprays earlier in the season. This has avoided flaring SLW and allowed beneficials to multiply and offer a free service to growers and consultants in controlling whitefly.

Whitefly numbers are reportedly building up at St George/Dirranbandi. DPI&F entomologists will be visiting the area next week to collect samples for resistance monitoring and check parasitism levels.

While whitefly are definitely starting to make their presence felt in cotton fields across Queensland, their presence does not necessarily warrant action. Monitor fields often as whitefly can build up exponentially, identify what species/biotypes are present, use the available thresholds and avoid flaring whitefly by minimising the use of disruptive insecticides and maintaining beneficials in the system.

Article by Zara Ludgate

Where do mirids come from?

In order to make this decision, we need to understand the population dynamics of mirids, their damage potential and what is currently happening to the crop.

What is happening this year?
Although the past winter was relatively wet, mirid numbers have been very low across the cotton growing areas so far this year. The reason for this phenomenon is not well understood. It could be that alternative hosts are still fresh enough to continue to support mirids, or the severe and prolonged winter may have had a detrimental effect on mirid populations.

Do we need to be worried about square loss at this stage?
If square retention is above 70% and mirid numbers are very low (as is the case for many crops this year), there is no need to be unduly concerned. Squares may be lost for various reasons e.g. insect feeding and physiological reasons.

If mirid numbers are very low and retention is less than 70%, square loss may be due to reasons other than insect feeding and a spray will not help. Square loss at this stage will be compensated fully provided plants do not further suffer from water or nutrient stress or from any other insects.

Figure 1. Compensation for mirid damage at squaring stage

Figure 1 shows plant mapping data in Bollgard® II..

Observation 1 shows the percentage fruit loss for 3 treatments at the squaring stage while observation 2 shows the same 3 treatments at cut out. The treatments consisted of the following:

In treatment 1 (blue) plants were sprayed on a regular basis starting from when 60% of plants had their first flower until cut out. Treatment 2 (red) was not sprayed for mirids at any time during the season. Treatment 3 was sprayed regularly throughout the season to provide total protection against mirids

In observation 1 – the squaring stage – there is a significant difference between treatment 1 (sprayed from squaring) and treatment 3 (sprayed all season) with 18% fruit loss for treatment 1 and 8% loss in treatment 3.
Consequences of unwarranted mirid sprays at this stage
There are several consequences of an insurance spray.
- It is an unnecessary expense.
- Disruption of benefcial communities at this early stage could flare secondary pests such as aphids, mites and whitefly.
- Sprays at this stage, whether high or low rate, will not provide long residual protection. Mirids could move in from alternative hosts at any time, and it is best to save the spray for when it is really warranted.

Article by Dr Moazzem Khan

However if we now look at what happened in these treatment at cut out, we find that there is no significant difference between treatment 1 and 3. What this shows is that in this experiment the plants had the ability to make up for the early season fruit loss.