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Aphids and IN PULSE CROPS fact sheet

JULY 2010

western and Southern regions Integrated control of is required to minimise the risk in pulses Aphids can damage crops by spreading viruses or causing direct damage when feeding on plants. Feeding damage generally requires large populations, but virus transmission can occur before aphids are seen to be present. Pre-emptive management is required to minimise the risk of aphids and their transmission of viruses.

KEY POINTS ■ Viruses are widespread in pulse, cereal and oilseed crops throughout southern and western Australia and can cause significant economic losses, especially when extensive infection occurs in early crop growth. ■ Aphids are the principal, but not sole, vectors of viruses in crops; some are also transmitted in seed. ■ A few aphids can cause substantial damage if they are spreading viruses, especially early in the season. It takes large numbers of aphids to damage crops by Killing the green bridge minimises host plants for viruses and aphids. Sowing into stubble, direct feeding. ideally inter-row, reduces the bare soil that is attractive to some aphids. Both of these are ■ Different species transmit important practices to prevent young crops being infected by viruses introduced by aphids. different viruses to particular crop types; species identification is important because management Virus damage in pulses can result in About aphids strategies can vary. reduced yield and seed quality. To minimise virus damage in pulse crops ■ Aphids are small, soft-bodied Pulses are annual crops – it is important to control the spread of that grow up to 4 millimetres in length. aphids and the viruses they aphids. spread have alternative hosts Adult aphids can be winged or wingless between seasons. Early season rainfall can trigger the – all immature aphids are wingless. germination and growth of weeds ■ Aphid population development There are at least 18 aphid species and volunteers that provide food and is strongly influenced by local found in broadacre crops across refuge for aphids and can act as conditions. Early breaks and southern Australia, but not all of a source of viruses. The source of summer rainfall favour early these are of economic importance to viruses is likely to be greater if last increases in aphids and volunteers broadacre agriculture. year’s crops were infected. The that host viruses, resulting in a extent of the early build-up of aphid Some aphid species will colonise higher level of virus risk. populations determines the level of individual plants, while other aphid ■ Integrated management practices seasonal risk. Diseased seed is another species will move through a crop that aim to control aphid source of some viruses. and be very difficult to detect (see populations early in the season Identification). Using an integrated approach to are important to minimising virus both aphid and virus management Aphids’ ability to infect a plant with spread. is needed to reduce the risk of a virus depends on the combination yield loss. of aphids and virus (Table 1).

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Aphid identification P h o t : S A RDI P h o t : D A FW P h o t : S A RDI P h o t : S A RDI A

Green peach aphid aphid aphid Bluegreen aphid (Myzus persicae) ( pisum) (Aphis craccivora) () Typically a pale green colour and About 4mm long, pea aphids can Charcoal grey through to shiny Bluish green in colour, they grow found on the underside of older be green, yellow or pink and have black in colour, with black and to approximately 3mm long. leaves. They cause less direct black knees and dark joints on white banded legs. These aphids These aphids spread more evenly feeding damage than other aphid their antennae. They attack faba tend to colonise single plants over a crop than cowpea aphids. species. Green peach aphids beans, field and lucerne, but or groups of plants in hot spots Sometimes certain plants will host spread relatively uniformly are often absent from pea crops. within a crop, infesting the a heavy population of these aphids, through a crop. They primarily growing points. Cowpea aphids while nearby plants may only have attack canola, lupins and some primarily attack medics, lupins, a few. They primarily attack annual other pulse crops. faba beans, and vetch. medic and subclover pastures, lupins and lucerne.

Other aphids – such as corn aphid (Rhopalosiphum maidis), oat aphid (Rhopalosiphum padi), and rose-grain aphid (Metopolophium dirhodum) – are found in cereal crops and pasture grasses where they can cause substantial damage by spreading viruses such as the barley yellow dwarf virus. Cabbage aphid (Brevicoryne brassicae) and turnip aphid (Lipaphis erysimi) are frequently associated with feeding damage on canola.

Management strategies can vary plants and the secretion of honeydew, Pre-season rainfall and availability of depending on the aphid species which supports secondary growth of a green bridge of weeds and and the virus it is carrying (see sooty mould. These symptoms can volunteers will favour an early increase Management strategies). help early identification of aphid hot in aphids, and these plants may spots in a crop. also host viruses. The extent of this Aphids can spread viruses early build-up determines the level of persistently or non-persistently. Lifecycle seasonal virus risk. Once an aphid has picked up a Aphids reproduce very quickly, giving persistently transmitted virus – for Aphid migration starts in autumn birth to live young, and have winged example, beet western yellows virus when winged aphids fly into crop (alate) and wingless (apterous) adult (BWYV) – it carries the virus for life, edges and start colonies of wingless forms. infecting every plant where it feeds aphids. Cold winter conditions slow on phloem. Aphids carrying non- Over summer, aphids survive in low reproduction until spring, when persistently transmitted viruses, such numbers on alternative host plants such reproduction is rapid, leading to as (CMV), as weeds and volunteer grasses along population outbreaks. carry the virus temporarily and only roadsides. A wet summer or irrigated infect new plants in the first one or crops will mean more green plants and When host plants die, become two probes. larger populations of aphid surviving unsuitable or overcrowded, Important vectors for non-persistent between winter growing seasons. aphids develop winged forms and migrate to other crops. viruses in pulse crops include green Hot dry summers and late breaks with peach aphid, pea aphid, cowpea cooler weather can lower the risk of During heavy infestations, plants aphid and bluegreen aphid, which will autumn aphid infestations in newly can be covered with white cast-off colonise pulse crops. Turnip aphid, sown crops. aphid skins. maize aphid and oat aphid, which are non-colonising species, will move through pulse crops, probing as they go and potentially spreading viruses. Table 1 Transmission of one persistent and two non-persistent viruses by four aphid species. Green peach aphid and pea aphid are also important in spreading Pea seed-borne Beet western persistently transmitted viruses, Cucumber mosaic virus yellows virus Aphid species (non-persistent) mosaic virus depending on the virus involved (non-persistent) (persistent) (Table 1). Green peach aphid    If seed or host plants infected with Pea aphid   viruses are not present, then aphids will only cause damage by direct Cowpea aphid    feeding on sap and nutrients. This leads to wilting and yellowing of Bluegreen aphid  PAGE 3

Plants can suffer up to 100 per Sticky traps might assist in identifying Viruses cent yield loss from virus infection, early aphid activity, as well as the Viruses transmitted by aphids to pulse especially if infected early in the presence of beneficial insects. season – usually within the first 10 crops occur in all rainfall environments, Beneficial insects – including hover but not all are economically important. weeks of emergence. Overall, crop loss is dependent on the growth flies, lacewings, ladybirds and The main non-persistently transmitted stage at infection and the number of parasitic wasps – will attack aphids viruses are: plants infected. Early and widespread and assist in preventing aphid levels infections result in the greatest losses. from increasing. Beneficial insects can ■ cucumber mosaic virus (CMV); help reduce virus spread and spring ■  (BYMV); Pulse crops damaged by viruses feeding damage, but some virus develop few and smaller seeds with spread will have occurred before aphid ■  mosaic virus (AMV) and; reduced seed quality. Pea seed-borne numbers subside. ■ mosaic virus discolours seed. pea seed-borne mosaic virus (PSbMV). The risk of non-persistently The main viruses transmitted persistently If a virus is introduced at low levels and transmitted viruses can be reduced are: late in the season, visible symptoms by an integrated disease management and yield reduction are unlikely. approach applied prior to seeding that ■ beet western yellows virus (BWYV) However, these visually non-detectable includes a range of crop hygiene and and; levels of infections can contribute to management measures. ■ bean leaf roll virus (BLRV). seed infection with viruses such as CMV, BYMV, AMV and PSbMV. Insecticide applied as seed dressings The same virus can infect several will help control aphid attack and the different species of pulses (Figure 1). Virus transmission in chickpeas differs spread of viruses. from other pulse crops, as the crop is During summer and autumn, viruses not colonised by aphids. Winged aphids Foliar insecticides applied soon after survive in alternate host plants such as will move through a chickpea crop and crop emergence can help control weeds, pasture legumes, lucerne and probe individual plants while looking for persistently transmitted viruses, but are self-sown pulses. a suitable host, leading to considerable of little benefit against non-persistently transmitted viruses. Preferably use a Viruses are spread by aphids whenever virus spread throughout the crop. ‘soft’ insecticide, such as pirimicarb they are moving in crops. Often the (registered for lupins only), that targets most significant spread coincides with Management the aphids and leaves beneficial a build-up of aphid populations before insects unharmed. sowing and the early movement of strategies winged aphids into young crops. An integrated management approach Integrated management to Some viruses are able to survive should be taken to reduce the risk of minimise virus transmission in pulse seed, which can create a virus transmission by aphids. ■ Minimise the pool of potentially source of infection within a crop. CMV, virus-infected plant material near BYMV, AMV and PSbMV can all be Early monitoring of target crops for crops by controlling the green transmitted by infected pulse seed. aphids is of limited benefit for virus control for two reasons. Firstly, non- bridge of weeds, pastures and The transmission rate of viruses colonising aphids may be involved and, volunteer pulses that can harbour from seed to seedlings varies widely second, even when colonising aphids viruses and aphids over summer or depending on the virus and crop type. are involved, critical early virus spread between crops. This includes weeds Up to 75 per cent transmission rates tends to occur before enough aphids around dams, tracks and the margins have been reported for CMV in lupins are present to be observed. of crops. and PSbMV in peas. S O UR C E : DPI VI All seed samples should be tested to FIGURE 1 An example of the level of viruses in different pulse crops. determine if they are infected with virus. This data is for pulse crops grown in South Australia between A threshold of less than 0.1 per cent 2001 to 2009 seed infection is recommended for sowing in high-risk areas, and less than % of crops infected 90 0.5 per cent seed infection for sowing in low-risk areas. The threshold with 80 PSbMV in field peas is less than 0.5 70 per cent in high-risk areas. 60 BWYV and BLRV are not seed borne 50 and can only be introduced to crops 40 from external sources by aphid 30 transmission. 20 Virus damage 10 0 Virus symptoms vary widely depending Lentils (78) Beans (82) Peas (56) Lupins (17) Chickpeas (19) Total (252) on the virus and crop combination. Number of crops in brackets Symptoms range from mild mosaicing Cucumber mosaic virus Beet western yellows virus Bean leaf roll virus and yellowing to severe leaf Pea seed-borne mosaic virus Bean yellow mosaic virus deformation, wilting and stunting. Subclover stunt virus PAGE 4

■ Source clean seed and test retained dressing on susceptible crops to Control the aphids if virus spread seed for viruses including CMV, prevent aphids attacking emerging and direct feeding damage is BYMV, AMV and PSbMV. Sow crops and spreading the persistently of concern. tested seed with less than 0.1 per transmitted viruses BLRV and BWYV cent virus infection to reduce the early in the season. Controlling direct feeding damage pool of virus-infected material. Field ■ Alternatively, a foliar insecticide can Monitoring crops for direct feeding pea seed should have less than 0.5 be applied early based on forecast per cent PSbMV. damage can be worthwhile. There reports of the degree of risk. is limited threshold information on ■ Some varieties have virus resistance. Preferably use a ‘soft’ insecticide, aphid numbers to determine whether Resistance to CMV seed transmission such as pirimicarb (registered for it is economically worthwhile to apply has been bred into many new lupin lupins only), that targets the aphids insecticides to prevent damage caused varieties including JenabillupA. and leaves beneficial insects by feeding. Research in WA suggests YarrumA field pea has resistance to unharmed. There is debate over spraying if more than 30 per cent of BLRV and PSbMV. Pulse Breeding the use of synthetic pyrethroids lupin growing tips are colonised by Australia (PBA) is increasing its (SP) as a foliar application – it is aphids from the flower bud stage emphasis on developing pulse crop recommended to prevent BLRV through to podding, especially in lines with increased virus resistance. transmission as it has so called aphid-susceptible varieties. Thresholds Faba bean lines with resistance to ’anti-feed’ properties that prevent should only be considered as a BLRV and field peas with resistance early colonising of crops by pea guide as many factors influence the to BLRV and PSbMV have been aphids. However, discouraging economics of spraying. identified and should be commercially colonisation may increase the available in the future. spread of aphids and, potentially, Routine spraying of SP insecticides virus through a crop. should be avoided as repeated ■ Some species of aphids are applications of these insecticides attracted to areas of bare earth. ■ SP insecticides should not be used can result in resistance developing in Use minimal tillage and sow into to control green peach aphid, an other aphid species and will also kill retained stubble, ideally inter-row important vector of BWYV, as most many natural predators. to discourage aphid landings. This populations of green peach aphid A ‘soft’ insecticide such as pirimicarb applies especially to minimising are resistant to this insecticide. (registered for lupins only), is an CMV spread in lupins. ■ Monitor crops and neighbouring option for controlling direct feeding ■ Consider using neonictonoid areas regularly. Identify the species damage when aphid populations (Gaucho 350SD) insecticide seed of aphid present and their numbers. are increasing.

Useful resources: ■ Other related GRDC Factsheets ■ Pulse Australia agronomists www.pulseaus.com.au www.grdc.com.au/factsheets ■ Jenny Davidson, SARDI 08 8303 9389 ■ CESAR Consultants Email [email protected] www.cesarconsultants.com.au/services/agriculture ■ Kym Perry, SARDI 08 8303 9370 ■ Integrated Pest Management for Crops and Pastures Email [email protected] (2008), Paul Horne and Jessica Page, Landlinks Press – ■ Paul Umina, CESAR 03 9329 8817 copies available at www.ipmtechnologies.com.au Email [email protected] ■ Virus control in chickpea – special considerations and ■ Ground Cover Direct www.grdc.com.au/bookshop Virus management in pulses www.pulseaus.com.au free phone 1800 11 00 44 ■ Crop Insects: the Ute Guide – southern grain ■ For insecticide registration: www.apvma.gov.au/pubcris belt edition ■ Pest Genie www.pestgenie.com.au ■ Crop Insects: the Ute Guide – western grain belt edition ■ Seed testing laboratories ■ Back Pocket Guide to Beneficials ■ SARDI Field Crops Pathology 08 8303 0360 ■ Lentils: the Ute Guide ■ TASAG ELISA and Pathology Testing Service ■ Faba Beans: the Ute Guide 03 6233 6845 ■ Field Peas: the Ute Guide ■ AgWest Plant Laboratories 08 9368 3721 ■ Winter Pulse Disorders: the Ute Guide ■ Agrifood Technology 03 9742 0555 ■ GRDC Pest Links www.grdc.com.au/pestlinks ■ CASCO Agritech 07 4633 0599 Disclaimer Any recommendations, suggestions or opinions contained in this publication or arising by reason of any person using or relying on the information in this do not necessarily represent the policy or views of the Grains Research and publication. Development Corporation. No person should act on the basis of the contents of CAUTION: RESEARCH ON UNREGISTERED PESTICIDE USE this publication without first obtaining specific, independent professional advice. Any research with unregistered pesticides or of unregistered products reported The Corporation and contributors to this Fact Sheet may identify products by in this document does not constitute a recommendation for that particular use by proprietary or trade names to help readers identify particular types of products. the authors or the authors’ organisations. We do not endorse or recommend the products of any manufacturer referred to. Other products may perform as well as or better than those specifically referred All pesticide applications must accord with the currently registered label for that www.coretext.com.au to. The GRDC will not be liable for any loss, damage, cost or expense incurred particular pesticide, crop, pest and region.

Acknowledgements – Kym Perry, SARDI; Peter Mangano, DAFWA; Paul Umina, CESAR; Angela Freeman, DPI Vic; Roger Jones, DAFWA; Wayne Hawthorne, Pulse Australia; Jenny Davidson, SARDI. produced by