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PestFacts Issue No. 7 - 19th August 2016
Cereal aphids gain a foothold before spring Oat and corn aphids aren’t hard to spot at the moment, but think twice before reaching for the broad-spectrums…
Where have they been reported?
Often collectively referred to as cereal aphids, oat aphids (Rhopalosiphum padi) and corn aphids (Rhopalosiphum maidis) are building up in cereal crops in many regions of south-eastern Australia. High populations of oat aphids are in wheat and barley crops in the Condobolin region of the NSW Central West Slopes and Plains. Reports of oat aphid have also arrived from the NSW Riverina, including barley crops northeast of Albury and near Lockhart. Corn aphids have also been observed in cereal crops in this region.
In Victoria, oat and corn aphid activity has been reported by agronomists and observed by cesar consultants in cereals across many locations in the Mallee, Wimmera and North East. Some populations of oat aphids have been found cohabiting crops with Russian wheat aphid (RWA, Diuraphis noxia). Oat aphid populations greater than 100 aphids per plant have been observed in numerous wheat paddocks around Elmore in Victoria’s Northern Country.
Cereal aphids gain a foothold before spring
Look out for Russian wheat aphid - 'sprinter' is upon us
Partners in crime - update on armyworms and 'herringbone caterpillars'
Has pasture day moth caught your attention?
Tell-tale features of a brown pasture looper
Free resistace testing service for redlegged earth mites
About cereal aphids
Oat aphids have a pear-shaped body and are olive-green to almost black in colour. They have distinctive rusty red patches around the aphid’s two ‘exhaust pipes’ or cornicles located toward the tail end of its body. The antennae extend about half the length of their body.
Corn aphids have an oblong shaped, light green to olive-coloured body with two dark areas near the base of the ‘exhaust pipes’.
While oat aphid and corn aphid are the two most prevalent cereal aphids in south-eastern Australia, rose-grain aphids (Metopolophium dirhodum) can also infest most cereals and some grasses. They have green-yellow bodies with a darker green stripe down the middle of the back. Rose-grain aphid could at first glance be mistaken for RWA. However the key is to take note of the aphid’s ‘exhaust pipes’. These are visible to the naked eye on rose-grain aphids but not on RWA.
Oat aphids are globular in shape (left), while corn aphids are oblong-shaped (right). Note the typical red colouration near the ‘exhaust pipes’ of oat aphids (Source: cesar)
Visit our PestNotes on oat aphid and corn aphid for more information.
Impact of aphid feeding
Oat and corn aphids can invade crops at any time between seedling stage and grain fill. Early infestations can cause reduced tillering, stunting and early leaf senescence. Later infestations on leaf sheaths and flag leaves between booting and the milky dough stages can also result in yield losses. In some cases, aphid colonies infest the seed heads and congregate in large numbers. After grain fill, aphid feeding has minimal or no impact on yield. Secretion of honeydew can cause secondary fungal growth, which inhibits photosynthesis and can decrease plant growth.
There have been numerous reports received this year that suggest crops treated with insecticide seed coatings (e.g. imidacloprid) have considerably fewer cereal aphids at present.
Our advice
The recent surge in cereal aphid numbers can likely be attributed to milder than average temperatures this winter. Healthy, unstressed cereal crops can sustain relatively large populations of cereal aphids before yield losses from direct feeding occur.
For example, an established economic threshold for winter cereal crops is 15 aphids per tiller on 50% of tillers, where yields are expected to surpass 3 t/ha. Given the current forecast conditions are likely to favour the ongoing build up of aphids during tillering and stem elongation, chemical controls may be warranted before populations peak.
However, keep in mind that corn aphid populations naturally decline as the crop starts to boot and approach heading. Similarly, host suitability may decline as cereal crops become reproductive with respect to oat aphid infestations (see The BeatSheet for further information).
If spraying is required, we strongly recommend using selective insecticides (e.g. pirimicarb) instead of broad-spectrums as they are less harmful to beneficial insects and therefore unlikely to induce a secondary pest outbreak. This is particularly relevant at the moment given it is still relatively early in the season. Beneficials invariably play an active role in keeping aphid and caterpillar (e.g. armyworm) populations in check.
Sources of field reports of cereal aphids
Chris Baker – Agronomist, Baker Ag Advantage (Central West Slopes and Plains NSW)Rebecca Bingley – Agronomist, Landmark (Riverina NSW)Pat Connell – Consultant, PC Agronomy, (Riverina NSW)Simon Craig – Consultant, Agronomise, (Victorian Mallee)Andrew McMahen – Agronomist, Landmark (Victorian Mallee)Luke Maher – Agronomy consultant, AGRIVision Consultants (Victorian Mallee)Warwick Nightingale – Agronomist, Delta Ag (Riverina NSW)Greg Toomey – Senior Agronomist, Landmark (Victorian Northern Country)Matt Watt – Agronomist, Baker Ag Advantage (Central West Slopes and Plains NSW)
Twitter sources
Grassroots Agronomy (@grassrootsag)Barry Haskins (@agrobaz)Rick Rundell-Gordon (@rick_rundell)Matt Witney (@DMAg_consultant)
Look out for Russian wheat aphid – ‘sprinter’ is upon usThe first detections of Russian wheat aphid in NSW have surfaced, but will populations flare as winter-spring conditions warm? In any case, monitoring is a must!
Russian wheat aphid (Source: cesar)
Where have they been reported?
Russian wheat aphid (RWA, Diuraphis noxia) has now been confirmed at two locations in NSW; the first near the town of Barham, and a second in a wheat crop in the Erigolia area, both in the Riverina district. The distribution of RWA in Victoria seems to have stabilised over winter, according to Agriculture Victoria’s Public Information Map. The aphid has been found in the Wimmera, Mallee, Northern Country and Central districts, as far east as Werribee. RWA have not been identified in Tasmania or Queensland.
About RWA
Information on RWA can be found in PestFacts south-eastern Issue No. 3. and Issue No. 4, and at the Plant Health Australia website.
Our advice
Activity of RWA is subdued by the cooler and wetter conditions of winter. Nonetheless, Victorian and South Australian field reports suggest that breeding has continued slowly over winter. Population growth will escalate as temperatures warm. The ’sprinter’ period of August and September, when rapid crop growth commences, is expected to be a high-risk period for crops infested with above-threshold RWA populations.
Consistent with the GRDC RWA F.I.T.E. strategy, we recommend:
1. Find RWA through regular Monitoring. Finding symptoms of RWA (pale and reddish streaking on leaves, leaf rolling and curling, tillers collapsing sideways, cereal heads being trapped in a hook in the boot) are easier than finding aphids, but can also be challenging. We suggest first looking:
• on crop edges where aphids first invade,• in areas of crop stress such as on diseased plants, on water challenged crop rises or areas of
compacted soil,• in areas where cereal volunteers germinated in March/April.
Given the aphids ability to reproduce quickly, we recommend regular monitoring.
2. Identify RWA and distinguish from other cereal aphids.
Seek help through an agronomist or entomologist. The use of a hand lens or other magnification tool is critical for this.
The most obvious diagnostic features include the (almost) absence of the usual aphid cornicles or ‘exhaust pipes’, two tail-end projections or caudate, and the long slender, spindle-like appearance of RWA. In NSW, RWA suspected detections must be reported through the Exotic Plant Pest Hotline 1800 084 881, or in Victoria, through the CropSafe program.
3. Apply economic thresholds.The beginning of the high-risk period for RWA is approaching. From early booting until soft dough, crops will not need a spray unless the current industry threshold for RWA applies: 10% of tillers with RWA symptoms. This threshold, based on international experiences, will need to be tested under Australian conditions.
4. Enact management strategies
• Consider the role of natural enemies in suppressing aphid and caterpillar populations and avoid the prophylactic use of insecticides. Natural enemies including ground beetles, spiders and predatory mites on the soil surface, and crop canopy beneficials including wasp parasitoids, lady beetles, hoverflies, lacewings, predatory bugs and various pathogenic fungi all attack aphids.
• Use registered products and especially those offering a vapour effect: pirimicarb 500 @250g/ha or chlorpyrifos 500 @600ml/ha (registered under an Emergency Use Permit). Pirimicarb, which is relatively soft on natural enemies, is recommended, especially as day temperatures increase.
• Good spray coverage / penetration is essential as many RWA will be ‘sheltering’ in the tight leaf roles. Use a water volume > 80 L/ha up until canopy closure, and 100-120 L/ha thereafter. Include a non-ionic surfactant with mid-size droplets.
• Crops with moderate damage can recover well after spraying.
• Spraying insecticides can kill foraging bees – advise beekeepers or visit BeeAware: beeaware.org.au before spraying. Bees forage over many kilometres of crop and can be tending weeds in cereals.
While the RWA may appear during spring in many previously unreported areas, the risk of the aphid causing serious crop loss in these areas is untested and probably not great. Nonetheless, regular crop monitoring should be a key management strategy.
Partners in crime - update on armyworms and ‘herringbone caterpillars’Armyworms and ‘herringbone caterpillars’ continue to be found together in cereal crops, although armyworms are becoming more dominant…
Armyworm (left) (Source: Copyright © Western Australian Agriculture Authority, 2015) and ‘herringbone caterpillar’ (Proteuxoa sp.) (right) (Source: cesar)
Where have they been reported?
Since the last issue of PestFacts south-eastern, armyworms (Persectania ewingii or Persectania dyscrita) along with ‘herringbone caterpillars’ (Proteuxoa spp.) have been found in the Victorian Wimmera, Mallee and Northern Country, and in the NSW Riverina.
In the Wimmera (Rupanyup, Charlton and Warracknabeal areas), many barley and wheat crops planted into standing stubbles are experiencing light to moderate foliar damage by small and medium sized armyworms and in many cases, ‘herringbone caterpillars’ as well. The damage is now becoming more obvious although it was quite restricted only weeks ago (<1% of crop). In the Mallee, lupins have also been attacked by ‘herringbone caterpillars’, and possibly armyworms as well. cesar consultants have identified armyworms and ‘herringbone caterpillars’ causing light foliar damage to multiple cereal crops in the Wimmera, and peripheral damage to a wheat crop north of Benalla in the Victorian North East.
Irrigated grass pastures have been eaten out by armyworms in the Moulamien area of the NSW Riverina (see photo below).
Feeding damage by armyworms to grass pasture irrigation bays in the NSW Riverina (Source: Chris Lucas).
About these caterpillars
For a second consecutive year, armyworms are challenging cereal crops, through defoliation, particularly in western Victoria. This goes against the conventional wisdom that armyworms appear irregularly in seasonal surges and subsequently decline in pest status for a number of years.
For comprehensive information on armyworms, including their occurrence, lifecycle, behaviour and management strategies, go to armyworm within the PestNote series. Click here for more information on identifying and managing ‘herringbone caterpillars’.
Our advice
Ensure correct identification of caterpillars before deciding on the most appropriate management action required. The use of insecticides in early spring to control caterpillars may be necessary to protect crops from extreme defoliation. Be aware of the trade-off in eliminating the beneficials that, in many cases, control moderate aphid and caterpillar populations. The loss of beneficials can often induce earlier or secondary pest outbreaks.
Currently, most armyworm caterpillars are too large to pose a risk (from head lopping) to maturing barley later in the season. Wheat is rarely at risk of head lopping. Our pest model predicts the current generation of armyworms is very likely to cease feeding and pupate well before most barley crops are susceptible to head lopping. Armyworm caterpillars that are greater than 8-10 mm in length will stop feeding by 8th-20th of October. In most cases this is before the most vulnerable maturing stage of barley crops where large caterpillars can chew through the stem below the head.
Sources of field reports
Brad Bennett – Consultant, AGRIVision Consultants (Victorian Mallee)Ben Cordes – Agronomist, Tylers Hardware & Rural Supplies (Victorian Wimmera)Chris Lucas – Biosecurity Officer, Local Land Services (NSW Riverina)Luke Maher – Agronomy consultant, AGRIVision Consultants (Victorian Mallee)Matt McLoughlan – Agronomist, Mr Agronomy (Victorian Wimmera)
Twitter sources:
Kelly Angel (@kangel62)
Has pasture day moth caught your attention?Although considered a sporadic pest, the sunset colours of pasture day moth are hard to miss…
Where have they been reported?
In the Barham area of the NSW Riverina, pasture day moth caterpillars (Apina calisto) have been reported in pastures (50/m2) and in volunteer peas within a wheat crop. Further west in the Victorian Mallee, these caterpillars have been found predominately feeding on capeweed within an oat crop, and on barley grass. They have also been observed in large numbers in a pasture paddock south-west of Kerang. For the second time season we have had reports of this pest damaging crops in the Kaniva region of the Victorian Wimmera. This time the damage was reported in lucerne. Lower numbers of pasture day moth caterpillars have also been observed around Horsham in several cereal crops.
About pasture day moth
Pasture day moth larvae are visually striking, especially when fully grown. They are dark brown with reddish-orange and yellow markings, and two distinctive yellow spots near the posterior end of the body. They are also noticeably hairy with prominent bristles and grow to approximately 60 mm in length.
Pasture day moth caterpillar (Source: cesar).
Pasture day moth caterpillars most commonly attack broad-leaf weeds in pasture, such as erodium and capeweed. They occasionally damage cereal and pasture crops, canola, peas, sub-clover and phalaris grass. This typically occurs in paddocks where pasture day moth are present and broad-leaf weeds are dead or dying from a herbicide spray; the caterpillars will transfer off the dying host plants and onto nearby crop plants.
Pasture day moth passes through one generation per year. Eggs are laid in pasture and hatch with the autumn rains. Larvae feed during winter and spring. When they are fully grown, they may be seen burrowing into the soil, excavating a vertical tunnel where they pupate in a cell at the bottom.
Our adviceThe benefit of controlling pasture day moth is questionable in most years. The last substantial outbreak was in 2007 where pasture day moth were reported across much of southern NSW, mostly attacking cereals and emerging pastures.
Sources of field reports of pasture day moth
Bronwyn Hunt – Grower (Victorian Mallee)Simon Mock – Consultant, Clovercrest Consulting (Victorian Wimmera)Kate Wilson – Agronomy Consultant, AGRIvision Consultants (Victorian Mallee)
Twitter sources
Scott Burger (@scottburger00)
Laura Kaylock (@LauraKaylock)
Tell-tale features of a brown pasture looperBrown pasture loopers are active this winter cropping season. When is enough enough? And can you tell the difference between this looper and other similar grubs?
Where have they been reported?
Recent foliar damage from brown pasture loopers (Ciampa arietaria) has been reported in canola in South West and North East Victoria. Minor damage has also been observed in canola near Lockhart in the NSW Riverina.
In late July, brown pasture looper damage was also seen affecting a lucerne stand near Kaniva, in the Victorian Wimmera. Similarly, 2-4 larvae per plant were observed in an old lucerne stand west of Elmore in Victoria’s Northern Country. In the same district west of Rochester, foliar damage had occurred in young lucerne undersown with oats.
About brown pasture loopers
Brown pasture loopers are easy to identify once you know what to look out for. The distinctive feature is the two bright yellow wavy lines running down along the back.
Wavy yellow lines running down the back of the brown pasture looper (Source: cesar).
Brown pasture loopers can be confused with pasture day moth (Apina calisto) or ‘herringbone caterpillars’ (Proteuxoa spp.). To further confirm identification of a suspected brown pasture looper, flip the grub onto its back or side and observe how many sets of abdominal prolegs it has. These are the leg-like appendages that caterpillars use to move. While most caterpillars have four sets of these, brown pasture loopers only have one set. They use their single pair of abdominal prolegs and one pair of anal prolegs to move using a series of back arches, which results in a characteristic looping motion.
Brown pasture looper has only one set of abdominal prolegs (top), whereas pasture day moth has four (bottom) (Source: cesar).
Brown pasture loopers have only one generation per year. Adult moths emerge in autumn and remain active until about June. They typically lay eggs on plant leaves and stems in early to mid autumn. The caterpillars that hatch from the eggs grow to full size (20–35 mm) in about two months. Once larvae reach full size in early spring they pupate and remain dormant over summer. Brown pasture loopers are typically a problem for establishing crops, and become less concerning from late winter as they pupate and plants outgrow the caterpillars.
Our advice
Once caterpillars reach 30-35 mm in length, their damage potential is limited; they will soon pupate.
Control of brown pasture loopers can be assisted by natural enemies including parasitic wasps, which attack the eggs. They are also prey to spined predatory shield bugs and glossy shield bugs as young larvae. If chemical control is warranted, there are several insecticides registered against brown pasture loopers, however spot spaying or perimeter spraying is usually all that is required.
Click here for further information on brown pasture loopers, including lifecycle and management strategies.
Sources of field reports of brown pasture loopers
Ben Dumesny – Consultant, Premier Ag Consultancy Group (South West Victoria)
Chris Dunn – Agronomist, Landmark (Victorian Northern Country)
Bruce Larcombe – Agronomist, Larcombe Agronomy (Victorian Northern Country)
Simon Mock – Consultant, Clovercrest Consulting (Victorian Wimmera)
Free resistance testing service for redlegged earth mitesTake advantage of a free testing service to screen for resistance in mites, available to all growers and advisors thanks to GRDC…
Redlegged earth mites (Source: cesar).
cesar is again testing redlegged earth mites (RLEM, Halotydeus destructor) for insecticide resistance across southern Australia. Throughout 2016, this service will be free for Australian grain growers, thanks to funding from GRDC.
Resistance to synthetic pyrethroids (SPs) is already confirmed in a large number of populations of RLEM across the WA grainbelt, while some populations in WA also have resistance to organophosphates (OPs). As yet there are no confirmed cases of resistance in south-eastern Australia. However, growers must be vigilant because genetic studies demonstrate a genetic flow between the east and west regions of Australia. Recent research at The University of Melbourne has revealed resistance to SPs has evolved on more than one occasion in WA, demonstrating the potential for resistance in other States.
One of the major challenges the Australian grains industry is facing is the reliance on only three registered chemical groups to control RLEM – neonicotinoids as a seed dressing, and SPs and OPs as foliar insecticides. Hence, growers are limited in their options to rotate different chemical classes, though it is imperative that they do so.
The testing service is available across SA, NSW, Victoria and Tasmania. Any grower or advisor experiencing a chemical control failure involving RLEM, or suspecting issues with insecticide resistance, are encouraged to contact us to access this free service.
For more information please contact:
Dr James Maino
cesar
Ph: 03 9349 4723
Email: [email protected]
> In this issue
Cereal aphids gain a foothold before spring
Look out for Russian wheat aphid - 'sprinter' is upon us
Partners in crime - update on armyworms and 'herringbone caterpillars'
Has pasture day moth caught your attention?
Tell-tale features of a brown pasture looper
Free resistace testing service for redlegged earth mites
What is PestFacts?
PestFacts is a free e-mail service designed to keep growers and farm advisers informed about invertebrate issues – and solutions – as they emerge during the winter growing season. The service has a focus on pests of broad-acre grain crops.
We need your reports
PestFacts is produced on an ʻas-needsʼ basis and relies upon pest observations and field reports from our subscribers. If you have recently observed invertebrate pests (or beneficial species) in crops and pastures, please report it here.
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PestFacts map is an interactive tool that allows users to search and view historical pest reports across Victoria and NSW. The map is updated with each issue of PestFacts to include new reports.
How to acknowledge PestFacts?
With appropriate acknowledgement, cesar grants permission to reproduce information taken directly from PestFacts. To cite PestFacts: “McDonald G, Govender A & Umina P. PestFacts south-eastern (<<enter date published>>). cesar pty ltd.”
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