The Beat Sheet » Cotton

Collecting to assess Silverleaf Whitefly susceptibility to insecticides

Melina Miles — Thu, 01 Mar 2012 05:59:06 +0000

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.

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

admin — Wed, 29 Feb 2012 22:36:28 +0000

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

Green vegetable bug (GVB) in late cotton

admin — Thu, 23 Feb 2012 22:20:27 +0000

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

Broad mites in cotton

admin — Thu, 16 Feb 2012 05:59:04 +0000

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.

What are broad mites?

Typically broad mites are a tropical pest however they may be found in subtropical and temperate regions during periods of high humidity such as those experienced recently. Broad mites feed on a wide range of crops including capsicums, potatoes, citrus and cotton. They are tiny (adults are approximately 0.2-0.3mm long) and very difficult to see even using a x10 hand lens.

Broad mite females lay eggs on the underside of leaves. The eggs are oval, translucent and covered with five or six rows of white tubercles (nodules). The life cycle from egg to adult is between 6 and 9 days and includes two nymphal stages. Adults are white-yellow with males being extremely active and fast moving. Broad mites will spread from plant to plant by walking, although they are quite happy to hitch a lift on the legs of other small insects such as silver leaf whitefly.

Broad mite adults, nymphs and eggs on under surface of leaf. Photo courtesy David Astridge DEEDI

Damage symptoms

A sign that broad mites are present is usually distortion of leaves with the underside of these leaves having a ‘wet’ appearance even though it is dry. Symptoms may resemble those of 2,4-D damage with leaf margins curling downwards or upwards and leaves becoming hard and brittle.

In tropical regions severe infestations of broad mites have resulted in seed yield losses in cotton of between 11 and 54% when plants have been infested early and outbreaks remain uncontrolled. In Australia, broad mite populations can increase rapidly during favourable conditions particularly when humid conditions prevail. During periods of low humidity it is unlikely that populations will be sustained for long periods. Early infestations of broad mite can seriously stunt plant growth and may result in patchy yield loss across fields.

At present, the majority of cotton crops have set fruit and reached cut-out so the risk that infestations of broad mite will cause yield reductions is diminishing rapidly. Furthermore with humidity levels forecast to decrease to quite low levels we do not expect populations of broad mite to increase much beyond those encountered in crops at present.

Shiny wet appearance of leaf undersurface due to broad mite damage. Photo courtesy D. Lea

Management of broad mites

Broad mites are usually suppressed by natural enemies including lacewing larvae, predatory mites and minute pirate bugs. If other pests require control use selective options that conserve natural enemies. Addition of a petroleum spray oil may also help suppress the broad mites. Currently there are no pesticides registered for control of broad mites in cotton and it is doubtful that likely yield losses would warrant application for a minor use permit. It is however expected that growers applying chemicals such as abamectin for control of two spotted mite are also likely to control broad mite.

Article by Ian Taylor

This article first appeared in the Cotton Tales newsletter

Broadmites have also been reported in navybeans in central Queensland in recent years. The broad mites were thought to have come in from citrus orchards. The distinctive symptom of broad mites in navybeans is bronzing under the leaves.

Beware of Apple Dimpling bugs

admin — Fri, 09 Dec 2011 02:44:22 +0000

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.

Apple dimpling bug adult

Pest or predator?

ADB are well known as predators of helicoverpa eggs and mites. However, they are also plant feeders and on young cotton will feed on small ‘pin’ squares which results in shedding of the squares. Damage at seedling stage is unlikely to affect yield but will delay maturity by 4-5 days.

Damaged (left) and undamaged squares © Mary Whitehouse CSIRO

When do they need controlling?

Dr Moazzem Khan (DEEDI) has studied the responses of cotton to ADB. Based on his findings – current recommended economic thresholds for ADB is 10 bugs per metre row of cotton along with 50% fruit retention at the squaring stage.

Monitoring and sampling for ADB is best done early in the morning or late afternoon. ADB populations can be assessed visually as well as with a beatsheet (at the time of this study only visual sampling was used). Assessments should be conducted in the top half of cotton plants.

Overall visual sampling was the most efficient sampling method for ADB. However, at the seedling stage visual sampling, beat sheet sampling and suction methods were equally effective. As the plants mature, visual sampling was found to be twice as effective when compared to beat sheet sampling. This means that ADB numbers found with beat sheet sampling, from boll set onwards, should be multiplied by two to get a better estimate of the population in the field.

The decision to control ADB depends on both fruit retention and ADB numbers. However, bear in mind that ADB feeding can be very variable and the cotton plant’s ability to compensate for loss of pin squares, by retaining other squares that may otherwise have been shed, is usually quite good.

Control options

If the decision to control is warranted, it is essential to consider the risk of flaring secondary pests. As ADB are also predators, there is a risk that a decision to control them may increase the chance of mite population build-up. As an occasional pest there are few products registered for their control. A low rate of Fipronil is the softest registered option. The only other registered options, OPs (organophosphates), are not available in the IRMS until late in the season and would be highly disruptive to beneficial insects in the crop.

Article by Moazzem Khan and Susan Maas

Early season aphid identification and management considerations in cotton

admin — Fri, 02 Dec 2011 00:02:54 +0000

As the cotton season gets underway aphids are starting to be detected in crops, on ratoons, volunteers and weeds. Last season, there were some regions where Cotton Bunchy Top (CBT) was detected in crops towards the end of the season. To assess and manage the risk of yield loss caused by CBT, and minimise the difficulties of controlling insecticide resistant cotton aphids it is important to i) be able to correctly identify aphids in the crops and ii) consider how early season infestations (in crop and on nearby weeds) will be managed. <–more–!> There is a lot already written about aphids and aphid management in cotton. Follow the link to the Cotton CRC website to read more about aphid biology and ecology, alternative hosts, and strategies to manage (including managing insecticide resistance). http://www.cottoncrc.org.au/industry/Publications/Pests_and_Beneficials/Aphids__Bunchytop Identifying aphids in cotton There are a number of species of aphid that will establish in cotton, Cotton Aphid, Cowpea Aphid and Green peach aphid are the most common. Cowpea and green peach aphid will colonise cotton, but tend only to persist in cooler conditions. Cowpea aphids were present in cotton crops in Emerald in early November this year, but numbers have since declined. We have received samples of cowpea aphid and cotton aphid from cotton on the Downs this season. Key features used in the identification of aphids are illustrated below. Use a x10 hand lens to examine the aphid to see the tubercles, cornicles and cauda features. Illustration from aphid identification key: http://ipm.ucdavis.edu/TOOLS/KEYAPHID/typical.html Aphid impact on cotton Aphids have the potential to reduce yield by direct feeding and exude honeydew, resulting in sticky cotton. Early season infestations may result in CBT transmission, and subsequent yield loss caused by CBT. Research to date (Lewis Wilson et al.), has only detected CBT transmission by Cotton Aphid, although it is possible that other species may transmit at very low levels. Deciding if aphids need control Here I will cover some basic points to consider when monitoring for aphids, and in making an assessment of the need for, or timing of aphid control.

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

2011 IPM forum highlights

admin — Wed, 14 Sep 2011 00:08:45 +0000

More than 50 researchers, extension staff and industry representatives attended this year’s IPM forum in Toowoomba. The IPM forum is an annual event and brings together researchers and industry to discuss the latest research and developments in pest management for the Northern region. Topics presented at the forum consist of a mix of current research and industry-ready research outcomes. Below are extracts of some of the presentations that featured at the IPM forum. For more information about the forum or the range of topics, please contact Kate Charleston.

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.

IPM Forums for growers and advisers – Thursday July 28th, 2011

Melina Miles — Sun, 17 Jul 2011 05:15:02 +0000

These Forums, for growers and advisers, will provide an opportunity to hear about recent research into the management of insect pests in grains and cotton. Researchers will be able to discuss with you strategies and options for the upcoming season, what to look out for, and how to minimise your risk of losses caused by key insect pests.

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

Getting Pale Cotton Stainer identification right

admin — Wed, 22 Dec 2010 02:21:15 +0000

Over the past few weeks there have been reports of cotton stainers in cotton crops in Central Queensland and on the Darling Downs. This week we received photographs of ‘stainers’ from CQ which raised the importance of correct identification.

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)

Mirid research trials on the Darling Downs

admin — Wed, 01 Dec 2010 04:00:07 +0000

In order to keep you updated with entomology activities, the following article outlines the research trials to be conducted on mirids this season on the Darling Downs by Dr Moazzem Khan (Senior Entomologist, DEEDI, Toowoomba).

Mirids have become regular pests of Bollgard® II cotton. Despite the development of good crop-stage thresholds and IPM options for mirids, more research is needed to further improve mirid management in cotton.

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.