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.    

The latter damage is of greater concern. Terminal death (tipping) can result in crops setting pods low to the ground where they are more difficult to harvest. Damage in most crops has been uneconomic to date. 

Thresholds are determined at 25% terminal loss.   

However after the current rain event dies down, growers should re-inspect crops for any terminal death symptoms. Other early signs of infestation of this pest include the small blue-winged adults (butterflies) flitting over the crop, and the presence of their relatively large (0.6mm diameter) pale blue eggs.

Grass blue larvae are often confused with hoverfly larvae. They are of similar appearance and size but hoverfly larvae are key aphid and whitefly predators.. Hoverfly larvae are ‘true fly’ larvae or maggots and they differ from grass blue larva in that they do not have a head capsule, true segmented legs and fleshy prolegs.  

To confirm that you have pest (the grass blue larvae) and not the beneficial, flip them over to check for the (normally hidden) head capsule, 3 pairs of proper legs (at the head end) and 4 pairs of ventral prolegs.  These legs are positioned towards the larva’s mid-line and are not visible from above. Another way to confirm identity is to place the larvae in a jar with some leaves – the hoverfly larvae will not eat the leaves but instead rear up to look for prey while the plant pest will eat the leaves.

Hoverfly larvae                                Grass blue butterfly larvae

 Management

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. 

As the earlier plantings of sorghum progress through flowering, moderate to high Helicoverpa pressure means that many crops have caterpillar numbers over threshold.  Nucleopolyhedrovirus (NPV) is one of the main insecticides used to control Helicoverpa larvae in sorghum, however prevailing conditions play an important role in the speed and level of control achieved with NPV.

Cooler weather

Larvae need to be actively feeding when NPV is applied for good control to be achieved.  Because larval feeding rate is largely governed by temperature, NPV is recommended to be applied between 25°C and 35°C.  However good performance can be achieved under cooler conditions, with application temperatures above 18°C considered acceptable.  Temperatures below 15°C can cause larvae to stop feeding, and prolonged periods below 15°C may cause “cold shock”, with larvae taking a few hours of warmer conditions to recover.  For this reason, it best to delay applying NPV until temperatures have warmed to above 20°C following a cold night.

Applying NPV where rain is forecast

The likelihood of wet weather raises questions about how best to time NPV applications when rain is expected.  NPV is significantly more effective against smaller larvae, so delaying application can impact on performance.

Other key issues relating to NPV use

• Ideally apply NPV when larvae are less than 7 mm in length (2nd instar – small).  These size larvae are more effectively controlled with lower rates of NPV
• Do not target larvae over 13 mm in length (4th instar – medium) with NPV – control will be compromised and these larvae will do significant damage before succumbing to NPV infection
• There is no economic benefit in controlling larvae with NPV in pre-flowering sorghum

Article by Anthony Hawes

•  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

Prior to his time in the Burdekin, Paul was based in Biloela. During his 7 years in Central Queensland, Paul was involved in research related to the evaluation of biopesticides; trap cropping, natural enemy research and the evaluation of Magnet® (moth attractant) as a resistance management tool for Helicoverpa in Bollgard II cotton. Whilst in CQ, Paul was also involved in research to develop the economic thresholds for Helicoverpa in chickpea, in conjunction with Melina Miles.

During the Silverleaf Whitefly outbreak in Central Queensland, Paul worked with Richard Sequeira and Dave Kelly to support the cotton industry in developing and implementing management strategies. Consultants on the Downs may be familiar with Paul from his visits to the Downs during the SLW outbreak in 2006/07, providing advice on appropriate management tactics.

As part of the Entomology team, Paul has responsibility for R, D and E for both cotton and grains. He brings expertise in cotton production, insect pest management in cotton, biological control (his PhD focussed on the rearing and use of assassin bugs in IPM) and general field crops entomology.

 Contact Paul at DEEDI in Toowoomba on:  4688 1533, 0428 929172 or  Paul.Grundy@deedi.qld.gov.au 

                      Paul finds Dave Murray’s overalls are big ones to fill

The low SLW pressure observed last season challenged the resistance monitoring team to develop new collecting techniques as the current collection method of selecting leaves with red-eye nymphs is slow and laborious in a low pressure season. A new collection method was developed based on collection methods observed during the CRDC funded study tour to Arizona and California during 2010, which utilised a modified vacuum cleaner and this has been found to be highly effective this year. Thank you to Matthew Rogan and Chris Monsour who made collections during the season for the resistance monitoring program.

Collections were made from cotton growing districts in QLD and northern NSW; Emerald, Burdekin, St George, Mungindi and Narrabri. Due to very low whitefly populations, no whitefly were obtained from the Darling Downs. A total of 14 collections were made from the field and maintained in culture to be tested against all four registered SLW insecticides; Admiral^®, Pegasus^®, Talstar^® and Movento^®.

Resistance testing results indicate that SLW sampled from cotton growing regions remain largely susceptible to Admiral^®. However elevated resistance frequencies have again been recorded from regions such as Bowen and the Burdekin which have intensive mixed cropping farming systems. These higher resistance factors are reflective of a more frequent usage pattern for Admiral^® and demonstrate that problematic levels of resistance can develop to this product. This should remind growers and advisors of the importance of supporting the Insecticide Resistance Management Strategies (IRMS) in place within each region and ensure that only one application of each insecticide product is used per season to reduce selection pressure.

Testing for Pegasus^® indicates resistant individuals are present in the population in all samples tested however resistance frequencies have not increased since last season and therefore no changes are required to the IRMS at this stage. Pegasus^® is not registered in horticulture in Australia and is not used widely elsewhere in the world and there is limited information available on SLW’s propensity to develop resistance to this product. One of the few places where Pegasus has been used extensively is in Israel where this product has been used for 14 years in cotton without resistance developing.

Talstar^® has elevated resistance factors in both cotton and horticultural production areas in all samples tested. Resistance factors for cotton have not changed from past seasons however the very high levels recorded in horticulture (where Talstar^® is used more frequently) indicate SLW’s propensity to develop resistance to this insecticide. While Talstar^® is registered for SLW in cotton, it is not recommended for use due to the disruption it causes to natural enemies and poor performance against SLW (Talstar is not translaminar and therefore has poor contact with whitefly which sit on the underside of leaves).

  Bioassay in progress to test resistance of SLW to Talstar^®

Movento^®, the newest SLW insecticide option was also tested but as this is the first season that Movento has been registered for cotton no data is available from previous seasons to compare resistance factors. Initial data indicates that populations are highly susceptible (based on very steep slopes in full dose response assays) which is expected, given that this is a new product with a unique mode of action.

The 2010-11 annual resistance monitoring results for SLW were presented to the Transgenic and Insecticide Management Strategy (TIMS) technical panel for consideration in deciding the management strategy for the 2011-12 season. The outcome of this meeting is that no changes to management are required at this stage. Admiral^®, Pegasus^® and Talstar^® all have resistant levels present in the population but remain unchanged from previous seasons. Higher resistance levels have been recorded for Admiral^® and Talstar^® in horticulture in the Burdekin. Using a maximum of one application of these products within a season in compliance with the current IRMS will conserve the efficacy of these products for future years. 

 * Resistance Factor – A Resistance Factor (RF) refers to the dose that it takes to kill a resistant colony compared to a susceptible strain. For example, if a susceptible strain is killed by 1 unit of insecticide, and a resistant strain is killed by 10 units of insecticide, then the resistant strain is 10 times more resistant then the susceptible strain and is said to have a RF of 10. It is difficult to quantify RF as being either low, medium or high as SLW responds differently to individual insecticides and may develop field resistance at RF 10 for one insecticide, but may not develop resistance to RF 1000 for another insecticide. This is a limitation of resistance monitoring as monitoring can identify changes in resistance factors but can not predict when increasing RF will lead to field failure. Resistance monitoring is an integral component of any resistance management strategy but needs to be used in conjunction with other resistance monitoring strategies including field observation of insecticide efficacy.

Article by Zara Hall

Armyworm and helicoverpa in barley, wheat and oats.

There have been a number of reports of armyworm activity across the northern region in isolated pockets. Armyworm has the capacity to lop heads in barley, wheat and oats after the crops have turned. As the crop turns the stems dry down, but the nodes take longer to dry, staying green for some time after the rest of the plant is dry

                            Green nodes on otherwise dry barley plants

As a result, armyworm that had been feeding on leaf material before it dried off, feed on the only green part of the plant left, the nodes. When the larvae feed on the node below the head it results in the characteristic head lopping.

It is estimated that one large armyworm larva can lop up to 7 heads per day (armyworms are active mostly at night). At one larva per square metre, that equates to around 70 kg/ha of lost grain per day. A damaging larva may be active for up to 10 days before pupating (see previous Beatsheet posting on calculating armyworm damage in wheat http://thebeatsheet.com.au/winter-cereals/armyworm-in-wheat/).

Monitor for armyworm with a sweep net and look for evidence of larvae feeding in the crop – ragged leaves, frass along the rows and lopped heads. 

Helicoverpa may also be present in barley and wheat crops. Monitor for them in the same way as for armyworm. Helicoverpa tend to graze on developing grain and the impact of this damage is much less than that caused by armyworm because typically only a few grains per head are damaged. Helicoverpa do not head lop like armyworm.

                     Helicoverpa larva and grazing damage to barley head.

Helicoverpa in chickpea

As chickpea crops finish off, ongoing rain is resulting in some crops reshooting, providing green material on which helicoverpa can continue to feed. The impact of these larvae is limited if the bulk of the pods are dry and mature, even large larvae cannot penetrate a dry pod. However, immature pods and pods softened by regular rainfall are susceptible. 

These persistent larvae will turn up in beatsheet sampling, but it is more critical at this stage of the season to determine how susceptible the crop is, rather than focussing on the number of larvae on the beatsheet.

It may be appropriate to dessicate the crop, rather than wait for it to dry down naturally. Without green leaves or pods to feed on, helicoverpa larvae will not survive.

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 mites themselves are pale green with two dark spots (summer form), or red (end of season or overwintering form). Please note that two spotted mites and red spider mites are the same species.  In view of the mite reports to date, all mungbean crops adjacent to potential earlier maturing crops should be checked for TSM.

No miticides are currently registered in mungbeans so the only options for mite-infested mungbeans are crop oils such as Canopy.  Canopy is a more expensive crop oil option but is less likely to burn crops than cheaper products which don’t contain a ULV protectant.  The recommended Canopy rate is 2-3%, the lower rate is recommended if a repeat spray is required.  Note that 2-3% equates to 20-30 mLs per litre of water or 2-3L/ha where the total spray volume is 100L/ha.

Thorough spray coverage is essential with crop oils which can take up to one week to suppress mite populations.  If there is sustained mite pressure, which is often the case where mungbeans are adjacent to a mite source (e.g. cotton crops), repeat sprays may be necessary at 14 day intervals.  The action threshold is 30% of plants being infested.

Mites are easily flared through the injudicious use of non selective pesticides against other pests.  Pre-flowering helicoverpa infestations can be controlled with virus biopesticides such as VivusMax and Gemstar.  The latest guidelines for such products are to apply them only when in-crop temperatures are higher than 18⁰C, and ideally when higher than 25⁰C.  Alkaline spray tank water should be buffered with a buffering agent such as Li700.  For effective control, it is critical that helicoverpa larvae are detected while still small, i.e. no more than 7 mm in length, and that thorough spray coverage is achieved.  Remember that the above virus products only target helicoverpa caterpillars. 

To control helicoverpa during the flowering/podding stage use indoxacarb (Steward EC) which is more selective than older non selective pesticides such as methomyl, thiodicarb and the synthetic pyrethroids.  However do not mix Steward EC with Canopy as there are reports of the Steward EC settling out and blocking spray nozzles and filters.

Dimethoate sprays to control mirids are highly likely to flare mites.  To minimise the mite risk, consider applying a low rate of dimethoate (200-250 mL/ha) with a 0.5% salt adjuvant.  These rates have both proven efficacy against mirids but a greatly reduced impact on beneficial insects.

Spraying podsucking bugs with deltamethrin (the only registered insecticide for this pest) is also likely to flare mites.  To minimise the mite risk, delay spraying until pods are starting to fill.

Article by Hugh Brier and Kate Charleston