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. 

•  Identify the aphids
• Make an assessment of the level of infestation – % of plants with aphids. Look for aphids towards the top of the plant, at 3-4 nodes down from the terminal, under leaves.
• Mark, or record, infestations and revisit to determine if the population is spreading, increasing in size, and whether there is beneficial insect activity.
• If the infestation is spreading – this is the point at which to make a decision about control.
• Don’t wait until populations are out of control (>30% infestation) to act.
• Suppression of populations for example with a spray oil, may be sufficient to minimise the risk of spread and in situations where there is a high risk of CBT transmission.
• Large influxes or rapidly spreading infestations may warrant the application of pirimicarb.
• Early season spray decisions should take into consideration the potential disruption to beneficials that contribute to the subsequent control of aphids, SLW and mealybug.

 CBT and aphid infestations

• Crops at high risk of CBT are those close to reservoirs of CBT and aphids (weeds, particularly malvaceae species; ratoons).
• Early infection will result in more severe symptoms.
• However, do not start spraying aphids at first appearance in the crop. Large influxes of cotton aphid from CBT reservoirs represent a larger risk, in terms of CBT transmission, than a slow influx over a longer period of time.
• CBT symptoms will not appear in the crop for up to 8 weeks after transmission – don’t act on symptoms.

 Article by Melina Miles

 Biosecurity threats posed by Silverleaf Whitefly (SLW) transmitted viruses

Cherie Gambley, Senior Plant Pathologist with DEEDI, outlined the threat of virus transmission by Silver Leaf Whitefly  Bemisia tabaci, Biotype B.

SLW is capable of transmitting viruses from several different taxonomic virus groups. Out of all virus groups the Begomovirus genus pose the greatest threat to Australian cotton, grain, vegetable and nursery industries.

Silverleaf Whitefly

 Begomoviruses have become a significant constraint to horticulture and field crop production worldwide and are considered one of the major emerging viral threats to crop production. Losses in the order of billions of dollars – attributed to these viruses – have occurred in cassava in Africa, cotton in Pakistan, grain legumes in India and tomatoes in Florida. These losses and the inability to effectively control the diseases caused by begomoviruses has contributed to major socio-economic problems including food shortages and grower suicides in Pakistan and SE Asia.

One of these SLW-transmitted diseases, Cotton leaf curl disease (CLCuD), is a major biosecurity threat for the cotton industry. This disease is also capable of infecting and causing production losses to vegetable crops such as cucurbits, tomato, capsicum and chilli as well as ornamental horticulture species such as hibiscus. There are also at least five begomovirus species capable of infecting grain legumes, particularly soybean, mungbean and cowpea.

Begomoviruses

To address the risk of begomoviruses, a cross-industry project has commenced with the aim of reviewing regional control of SLW as a virus vector, investigating the feasibility of using SLW indexing as an early warning surveillance tool for detection of exotic viruses and reviewing potential entry pathways for exotic viruses.

Pest Suppressive Landscapes and Habitat Function  

Nancy Schellhorn and Jamie Hopkinson gave an outline of the Pest Suppressive Landscape project. This project seeks to explore the link between surrounding habitats, pest and beneficial insect dynamics and pest suppression.     

Landscape complexity has been shown to increase the ecosystem service of pest suppression, although the mechanisms responsible remain elusive.  Ecological theory predicts that early predation by a few predators can result in higher pest suppression than late predation by many predators.   

In the Lockyer Valley, we tested the effects of earliness of predator impacts on the suppression of Aphis gossypii (cotton aphid) in 19 horticultural landscapes that differed in landscape complexity. Predator impacts were manipulated using exclusion cages on sentinel aphid populations. The following treatments were used: 1) early predation (only during week 1), 2) late predation (only during week 2), 3) continuous predation (during both weeks), and 4) predator exclusion control.  We found that predators can have a significant impact on aphids, but only some landscapes contributed predators early.     

On the Darling Downs we are identifying the source habitats of pests and natural enemies, assessing their movement between habitats and determining their time of crop colonization. To date we have determined that native vegetation has higher densities of beneficials, and infrequently harbour pests. Crops near this native vegetation have more beneficials than crops that are located further away. In both landscapes, pest densities are higher for crop further away from native vegetation than for crops that are nearby native vegetation.  These results will contribute to guidelines for IPM at the field, farm and landscape scale.  

Solenopsis mealybugs: farm hygiene and IPM  

Melina Miles and Susan Maas provided an update of solenopis mealybug. Outbreaks of this pest have occurred in cotton crops in the Burdekin, central Queensland and most recently in Byee. Impacts have been locally damaging and resulted in plant death and reduced yield.  

Mealybug specimens from cotton and other hosts have been submitted to the DEEDI taxonomists over the past 3 years. The current situation in cotton is that the distribution is still restricted to Queensland with no positive identifications from NSW cotton-growing regions.  Preliminary work by DEEDI has focused on addressing the immediate needs of the industry in terms of indentifying key sources of infestation, and controlling damaging infestations in-crop.  

Winter surveys of on-farm vegetation in the Emerald Irrigation Area found solenopsis mealybug on a number of weed hosts. Cotton volunteers and ratoons would appear to be key hosts; raising the perennial issue of crop and farm hygiene in minimising sources of insect pest infestations from one season to the next.  

Solenopsis mealybug on bladder ketmia host

 Whilst a permit has been available for methidathion to control solenopsis mealybug in cotton, the use of a broadspectrum option is unlikely to be the mainstay of mealybug control. Investigation into the population dynamics, impact of early infestations on crop growth and subsequent yield, and the potential of soft options to control infestations are warranted. CRDC has recently funded a 3 year project (2010-2014) which will include research that addresses key issues integral to developing a management strategy for solenopsis mealybug in the cotton-grains farming system.

The forums are being held at two locations on Thursday the 28th of July:

The  Dalby RSL:  9am – 11.30am

and

The Brookstead Hall:  1.30pm – 4.00pm

 Topics and presenters

 Cotton Bunchy top     

(Murray Sharman – DEEDI Virologist,  Lewis Wilson – CSIRO Entomologist, Jeff Werth – DEEDI weed scientist)

After the prevalence of cotton aphids and cotton bunchytop in some parts of the Downs, now is the time to start thinking about how to reduce aphid populations and remove sources of bunchytop that may otherwise invade your cotton crops next season. 

Seedling pests of cereals 

 (Hugh Brier – DEEDI Entomologist)

 Winter and spring crops are susceptible to a host of establishment pests, and cool and wet conditions can exacerbate the damage they cause. Learn what might be a problem this season, and how to identify the pest and its damage, and what you can do to control or manage the problem. Hugh will run through the common, and not-so-common, establishment pests.

Pest suppressive landscapes

  (Nancy Schellhorn - CSIRO Entomologist  and Jamie Hopkinson – DEEDI Entomologist)

Ever wondered whether the trees and shrubs along the creek, or in that nearby reserve were harbouring beneficial insects that might be benefitting your crops? Well, this is the focus of research being undertaken on the Downs, in NSW and WA. Nancy Schellhorn is leading a project that is examining the relationship between remnant vegetation and pest and beneficial abundance to answer questions about the role of this vegetation in the agricultural landscape.

Minimising the risk of a Solenopsis Mealybug outbreak 

 (Melina Miles,  DEEDI Entomologist)

You may have heard about the mealybug outbreak in Emerald cotton two seasons ago. You may be wondering if this new pest is coming your way. Melina has been involved in preliminary work on this pest, and will discuss some key management and monitoring strategies to minimise the likelihood of an outbreak in your crops.

For more information contact Melina Miles at the Toowoomba DEEDI office on 4688 1369, or 0407113306.  

Morning and afternoon tea will be provided. For catering purposes please RSVP to melina.miles@deedi.qld.gov.au

The photograph below is of a species called Graptostethus servus (seed eating bug), which has been collected from crops in CQ and on the Downs. This species of seed eating bug is not known to cause damage to cotton, but is potentially damaging in grain crops such as sorghum, soybean, mungbean and cowpea. However in southern Queensland at least, G. servus populations are usually far too low to be of economic concern.

Little is known about Graptostethus and its potential to damage cotton, so it is prudent to maintain a watching brief on the development of bolls in crops where Graptostethus may be present.  Note that this species can swarm with massive aggregations reported in orchards in the NT in the dry season.

 More information about this bug can be found on the following website:

(http://cotton.crc.org.au/content/Industry/Publications/Pests_and_Beneficials/Cotton_Insect_Pest_and_Beneficial_Guide/Pests_by_common_name/Seed_eating_bug.aspx)

Compare this to the pale cotton stainer (below), and you can clearly see the differences in the colour, and the markings. The pale cotton stainer is distinguished by the presence of a dark spot on the forewing, and a dark ‘collar’ behind the head.

Monitoring Pale Cotton Stainer numbers and impact on the crop

Monitor cotton stainer numbers with a beatsheet. A tentative threshold of 3 bugs per metre is proposed. Adults and 3-5^th instar nymphs are equally damaging.

Also monitor damage to developing bolls by cutting bolls open and looking for warty growths (in young bolls) or discoloured lint (older bolls). A threshold of 30% damaged bolls is suggested to prevent discounts for discoloured lint.

Pale cotton stainers will feed on both developing and mature cotton bolls, and can affect seed weight, oil content and seed viability. Heavy feeding on bolls less than 2 weeks old may result in shedding. Older bolls will suffer damage to developing seed, and potentially lint. Tightlock can occur around damaged seeds, lint may be discoloured (yellow), and feeding wounds may allow entry of fungi and bacteria that further damage the lint.

Further information on the damage potential and management recommendations for pale cotton stainer can be found in an article by Moazzem Khan, Lewis Wilson and Tracey Leven on the cotton CRC website.

(http://www.cottoncrc.org.au/content/Industry/Publications/Pests_and_Beneficials/Cotton_Pest_Management_Guide_2010__11.aspx)

 Green mirid adult                                                                    Green mirid nymph

Development of plant based thresholds

The aim of this trial is to determine the amount of fruit loss that occurs per mirid/day. and continues work from last season. Results from this trial will be incorporated into existing thresholds and will help growers and consultants to determine a threshold appropriate for specific fields given mirid activity and plant response.

The trials will be conducted at Nandi, Macalister and Jandowae with each site having 3 treatments. These treatments will be 1) unsprayed, 2) sprayed and 3) commercial (farmers management) resulting in different levels of mirid activity and damage.

Impact of mirid management on predators and parasitoids of whitefly
Management of mirids with broad-spectrum insecticides can lead to flaring of whitefly populations.

The word flaring is commonly used in entomology and refers to a population outbreak or explosion.

Anecdotal evidence suggests that broad-spectrum chemicals kill parasitoids and predators that play an important role in keeping whitefly populations in check. In absence of their natural enemies whitefly population grow rapidly in favourable environmental conditions.

The objective of this trial is to gather hard data to test this hypothesis. This trial will be conducted in Macalister with three treatments to create different disruption level scenarios.

The treatments consist of:
1) Spray at threshold using integrated pest management (IPM) control options
2) Spray at threshold with disruptive control options
3) Spray at below threshold with disruptive control options.

Pheromone traps as monitoring and management tools

 This trial will be conducted in Macalister by Dr Khan (pictured)  in collaboration with Dr Alice Del Socorro (University of New England, and CCC CRC).

The objective of the trial is to evaluate mirid pheromone traps as a monitoring and management tool.

Six traps baited with pheromone will be set up in a 4 ha (400 x 100) field.  An adjacent field, 500 m away without pheromone traps, will be used to compare mirid number and management.                                                                                  

For more information about these trials please contact the entomology team via the comments section of this blog posting.

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.