Aphid populations have built-up in some areas on the back of good summer and early autumn rains. And with crops in many regions, especially in Western Australia, suffering winter moisture stress, there is increased risk of higher levels of feeding damage from these insects in 2017.
In WA the past few weeks, the Department of Agriculture and Food WA (DAFWA) – now known as the Department of Primary Industries and Regional Development (DPIRD) – has received reports of green peach aphids (GPA – Myzus persicae), cabbage aphids (Brevicoryne brassicae) and turnip aphids (Lipaphis pseudobrassicae) in canola crops. These have mostly come from central and southern grainbelt regions.
There have been some reports of aphids in cereal crops on the south coast. DPIRD advises that climate model forecasts of below average rainfall and warmer daytime temperatures for this growing season in parts of WA are ideal for aphid reproduction.
Aphids consume more plant juices in warmer temperatures and inflict more damage when crops are young, increasing the susceptibility of water-stressed plants to production losses.
Aphid activity has been found to slow down if cold and wet weather conditions prevail. The Grains Research and Development Corporation (GRDC) and DPIRD researchers are urging growers and advisers to monitor all crops closely for aphid activity heading into late winter and spring.
Findings can be reported to the GRDC-supported PestFax service using phone, email or the PestFax Reporter mobile telephone app at: www.agric.wa.gov.au/diseases/pestfax-reporter. Paddock observations are a vital part of grains industry surveillance for the Russian wheat aphid (RWA, Diuraphis noxia) and will also assist researchers to produce aphid forecasts and alerts for particular areas.
RWA has not been detected in WA, but has caused significant damage to crops in South Australia and the eastern states since it was discovered in 2016. If in doubt, growers and advisers are advised to send any suspect aphid samples to agriculture and food offices at DPIRD for identification.
The department recently released a comprehensive guide to ‘Protecting WA Crops’ from aphids that can be found at: www.agric.wa.gov.au/newsletters/pwac/protecting-wa-crops-issue-3-june-2017..
COSTS OF APHIDS
Aphids cause crop and financial losses to growers through direct feeding damage, transmission of viruses (and other diseases), production of toxins and/or insecticide resistance management. Feeding damage by adults and nymphs during crop growth stages from seedling to grain fill can cause:
- death to seedlings;
- stunting;
- tiller or flower abortion;
- reduced seed set and size;
- lower grain yields.
DPIRD advises that the degree of feeding damage from aphids depends on the percentage of tillers or plants infested, the number of aphids per tiller or branch and duration of the infestation.
Oat aphids (Rhopalosiphum padi) and corn aphids (R. maidis) can transmit the costly Barley yellow dwarf virus (BYDV) in cereal crops, which (if crops are infected at the seedling stage) can reduce grain yields by more than 50 per cent. In the absence of viruses, oat aphid and corn aphid feeding damage can reduce grain yield by 10% if aphids are present from early tillering. RWA can inject a toxin into cereal crops that has caused yield losses of 80-100% overseas.
Of Australia’s aphid crop pest species, to date only GPA and cotton aphid (Aphis gossypii) have developed insecticide resistance. GPA are resistant to organophosphate (OP), carbamate and synthetic pyrethroid (SP) insecticides and, therefore, these products will not control GPA populations. Some GPA populations with low-level neonicotinoid resistance have also been identified, but neonicotinoid insecticides should still control populations with this type of resistance.
There is no resistance to Transform™ (sulfoxaflor) in Australian GPA populations and, therefore, this product will still provide control. For these reasons, it is advised to consider spraying GPA only if crops are at risk of not being able to out-grow damage.
APHID IDENTIFICATION
Correctly diagnosing the aphid species and size of population in crops will save growers time and money in control measures.
DPIRD researchers recommend regular crop monitoring during the seedling stage and only treating with insecticides if crops cannot outgrow damage. Patch spraying may be an option, but once crops are tillering or flowering the department advises using industry-recommended thresholds for insecticide applications.
This can help to ensure treatments are economic and effective in preventing grain yield or quality limitations. After aphids have been spotted in a paddock, there are a range of tools that have been developed with GRDC investments to help correctly identify the species and provide latest management advice for all crop types.
These resources can be found at:
- MyCrop hub: https://www.agric.wa.gov.au/mycrop
- PestFax at: https://www.agric.wa.gov.au/newsletters/pestfax
- GRDC-supported website: www.ipmguidelinesforgrains.com.au.
The DPIRD MyEconomicTool can be used to help assess the economic risk and financial costs associated with various aphid treatment strategies and can be found at: www.agric.wa.gov.au/wheat/myeconomic-tool?type=aphids..
Innovative technologies for faster and more accurate insect surveillance are also being trialled in WA this season by DPIRD researchers, funded by Royalties for Regions. These include DNA techniques, mobile device apps and SMART traps.
Department entomologist Dusty Severtson is testing an app for iPhones and android devices called ‘CropScout’. Tracking GPS locations allows this program to produce maps showing exactly where there are above-threshold levels of aphids.
The sampling protocols were developed after years of GRDC-supported trials into insect movement detection. CropScout is aimed at helping growers and advisers rapidly determine if insecticide sprays are necessary and provides an option to target specific areas where aphids have aggregated, such as along a crop edge or in a portion of crop.
SMART traps are also being investigated in WA in 2017 for monitoring and recording aphid (and native budworm moth, Helicoverpa punctigera) activity, providing valuable data for industry forecasts and alerts.
DPIRD development officer Christiaan Valentine has set up these automated aphid sticky traps that direct flying aphids to a yellow sticky card and send him a high resolution image of the card, via email, three times each day.
He can use the images to identify aphid species and potential population size to alert growers and advisers if they are flying into crops in the local area – without physically having to go out and check the traps.
MONITORING AND MANAGING APHIDS IN CANOLA CROPS
The main aphid types that attack WA canola crops are:
- turnip aphids;
- cabbage aphids;
- GPA.
Diagnostic information about these aphids can be found on DPIRD’s MyCrop website at: www.agric.wa.gov.au/mycrop/diagnosing-canola-aphids.
Turnip and cabbage aphids typically do the most feeding damage to canola, but GPA can be particularly destructive to moisture stressed crops and transmit viruses such as BWYV. Therefore, growers are warned to watch closely for these species in 2017.
Infestations of all species can be found in ‘hot spots’ or spread across a paddock and signs include aphids on growing points of plants and/or in clusters on buds and flowers. Growers are advised to check crops closely at flowering and note that yield loss is typically most likely when 20% or more of plants are infested with aphids at bud formation and flowering stages.
Cabbage aphid and turnip aphid can form population clusters on flowering spikes, whereas GPA is more likely to be found on the lower, oldest leaves on the plants. Insecticide applications on paddock borders may be warranted and economic at this threshold level, particularly for cabbage aphid. But in higher rainfall areas, canola can often recover from aphid infestations at flowering and yield loss does not typically occur when aphids are found in crops at podding stage.
DPIRD entomologist Svetlana Micic warns that, although less commonly found in WA, there may be big populations of GPA across the grainbelt this season.
She said this aphid is difficult to control, having resistance to pirimicarb, SPs and OPs, and it is vital to weigh-up whether or not to spray insecticides that aphids do not already have resistance to.
The National Insecticide Resistance Management (NIRM) group, headed by Dr Paul Umina from cesar, has developed a Resistance Management Strategy for GPA that contains information about how to best manage GPA in canola crops. This strategy can be viewed at: www.grdc.com.au/GPAResistanceStrategy.
Svetlana said the aim was to avoid over-using effective insecticides for GPA and potentially contributing to further resistance issues in future. She said it is advised to use an insecticide at label rates only once in a paddock and not at (or after) canola flowering stage, as research has shown GPA present at flowering do not cause yield loss in canola and spraying at this time does not typically lead to an increase in yield or oil.
MONITORING AND MANAGING APHIDS IN CEREAL CROPS
The main cereal aphid pests in WA are the corn aphid and oat aphid. RWA is now considered a high priority biosecurity risk for cereal crops in this State. Diagnostic and management information for cereal aphids can be found on the MyCrop website at: www.agric.wa.gov.au/mycrop/diagnosing-cereal-aphids.
Characteristics of the common species include:
- corn aphids – dark blue-green to grey-green;
- oat aphids – vary from mottled yellow-green through olive-green and dusky brown, to a blackish green and have a rusty patch on the tip of the abdomen;
- RWA – light green in colour, distinctive double-tail (cauda) and lack visible ‘exhaust pipes’ (siphunculi) at the top rear.
Oat and corn aphids can strike cereal crops at any time from seedling emergence to grain head development and signs of activity in the paddock include:
- patches of plants in crops with furled leaves;
- a ‘sooty’ appearance from feeding damage;
- colonies on the outside of tillers from base to stem;
- symptoms of BYDV.
RWA injects a toxin into cereal plants which causes pale streaking on leaves, similar to Wheat streak mosaic virus (WSMV).
Growers are advised to protect cereal crops during the first 12 weeks of growth – up to stem elongation – as BYDV transmission can occur even with low aphid numbers.
Research and experience in WA indicates applying insecticides to curb aphid feeding damage is typically worthwhile in wheat and barley crops that are expected to yield more than three tonnes per hectare and in which 50% of tillers have 10-20 or more aphids.
Parasitic wasps, ladybeetles, lacewings and hoverflies can provide useful biological control, mainly by preventing secondary outbreaks. This reiterates the importance of using ‘soft’ insecticides that only control aphids, such as pirimicarb.
MONITORING AND MANAGING APHIDS IN LUPIN AND PULSE CROPS
Aphid species commonly affecting WA lupin crops and other pulses include:
- cowpea aphid (Aphis craccivora);
- bluegreen aphid (Acyrthosiphon kondoi);
- GPA;
- leafcurl plum aphid (Brachycaudus helychrisi) – sporadic;
- potato aphid (Macrosiphum euphorbiae) – sporadic;
- pea aphid (Acyrthosiphon pisum) – in field peas.
Lupins are most vulnerable to aphid feeding damage during budding and flowering stages, when there is potential for:
- buds to drop;
- flowers to abort;
- seed set to be reduced.
As in cereals, aphids can also transmit diseases in lupins and some other pulses, including Cucumber mosaic virus (CMV) and Bean yellow mosaic virus (BYMV). Information about diagnosing aphid species in lupins can be found on the MyCrop website at: www.agric.wa.gov.au/mycrop/diagnosing-aphids-narrow-leafed-lupins.
Signs of aphids in lupin and pulse crops include wilted plants, insect clusters on buds and flowers, potentially winged adults and/or a ‘honeydew’ appearance on the plant surface. DPIRD advises that in susceptible lupin crops, yield losses of 30-90% are possible from feeding damage alone.
But some narrow leafed lupin varieties are moderately resistant to aphid colony development. Research and experience in WA indicates controlling aphids when 30% of flowering buds have 30 or more aphids can improve yields.
REPORTING APHID ACTIVITY
The GRDC-supported PestFax Reporter mobile app allows quick and easy reporting of aphid (and other pest/disease) incidence.
Grower, agronomist and adviser reports and observations provide accurate and timely data about aphid incidence and activity across WA cropping areas for every week of the growing season.
This information is collated and distributed via the PestFax Newsletter that can be found at: https://www.agric.wa.gov.au/newsletters/pestfax and the PestFax Map at: www.agric.wa.gov.au/diseases/pestfax-map.
PestFax services ensure growers and the wider grains industry are better informed about what is happening with pests across the WA grainbelt.
Entomologist Dr Siobhan de Little, of cesar, is conducting resistance testing on GPA, oat aphid and cowpea aphid this year. If you find any of these species in your crop, and particularly if you experience a control failure with GPA, make contact at sdelittle@cesaraustralia.com or send in your aphids, following the instructions at: www.cesaraustralia.com/assets/Uploads/PDFs/cesar-collecting-and-sending-GPA.pdf.
More information:
Svetlana Micic
DPIRD research officer, Albany,
08 9892 8591
svetlana.micic@agric.wa.gov.au
Dustin Severtson
DPIRD development officer, South Perth
08 9368 3249
dustin.severtson@agric.wa.gov.au
Dr Siobhan de Little
cesar research consultant, Melbourne
03 9349 4723,
