Aphids and their control on strawberry

Aphids are common and important pests of strawberry. They damage strawberry plants directly and two of themost common species, the strawberry aphid and the melon and cotton aphid, transmit virus diseases. Newaphicides recently approved on strawberry (Calypso, Plenum, Chess) provide improved opportunities for chemicalcontrol and the current trend to growing strawberries under protection provides greater opportunity to controlaphids biologically, by introductions of predators and parasites. This factsheet outlines the species that areeconomically important within strawberry production and outlines the various control options available.

Jerry Cross, Jean Fitzgerald and Graeme Down, East Malling Research

Factsheet 26/05

Strawberry

Project No. SF 61

HorticulturalDevelopmentCouncil

Bradbourne House

East Malling

Kent ME19 6DZ

T: 01732 848383

F: 01732 848498

E: hdc@hdc.org.uk

Pest identificationSeveral species of aphid are commonlyfound on strawberry in the UK. Straw-berry aphid, shallot aphid, potato aphidand the melon and cotton aphid are themost common, but many other speciesoccur occasionally. Glasshouse andpotato aphid is common underprotection.

The different aphid species causedifferent types of damage and requiredifferent control approaches. For thisreason, it is important to identify whichspecies are present and their relativeincidence. The different species arefairly easy to recognise by their appear-ance, distribution on the plant and thedamage they cause. Close examinationwith a hand lens may sometimes berequired for identification with certainty.

Strawberry aphid (Chaetosiphon fragaefolii)

Adults are small, whitish green withred eyes and their bodies are sparselyclothed with capitate body hairs(Figure 1, Diagram 1). Siphunculi(honey tubes) are moderately long.They are usually found on theundersides of leaves and, wheninfestations are heavy, on leaf petioles.

Diagram 1

1 Strawberry aphid (close up above and colony below)

Strawberry aphid showing forehead (right) and siphunculus (honeytube) (left). Note the presence

of capitate hairs, which sparsely clothe the aphids body and are particularly easily visible on the

forehead. These capitate hairs are only found on strawberry aphid.

Melon and cotton aphid(Aphis gossypii)

Aphids are very variable in colour,from bright yellow, to dark green toblack, with younger individuals in afamily group characteristically beinglighter and more mature individualsdarker (Figure 2). The legs are lighter,but not uniformly white (see blackbean aphid (Aphis fabae) below), andin common with other Aphis species,melon and cotton aphids have adomed head between the antennae.The aphid forms dense colonies thatsecrete honeydew copiously. Thisspecies is often resistant and survivestreatment with many aphicides.

Shallot aphid (Myzus ascalonicus)

Adults are small, pale brown oryellowish or greenish brown (Figure 3).The front of the head is emarginate(convex) between the antennae andprominences are slightly convergent(Diagram 2). Siphunculi (honey tubes)are distinctly swollen towards the tip(Diagram 2). This aphid is mainly foundin the growing points of plants, often insmall numbers and can be difficult tofind. However, unlike the other aphidsthat feed on strawberry, shallot aphidcauses noticeable stunting of thegrowth and characteristic twisting ofleaves (Figure 4).

2 Melon and cotton aphid (Aphis gossypii) adult, Ieft; aphids in strawberry flower, right

3 Shallot aphid

4 Shallot aphid damage to strawberry

Shallot aphid showing siphunculus (honeytube) which is distinctly swollen towards the tip and

the prominences on the forehead below the base of the antennae.

Diagram 2

7 Yellow rose aphid

5 Potato aphid on strawberry leaf

6 Glasshouse and potato aphid

Potato aphid(Macrosiphum euphorbiae)

Adults are large, with individuals in acolony ranging from yellowish-green topink. Siphunculi (honeytubes), are verylong, cylindrical and sometimes darktipped (Figure 5).

Glasshouse and potatoaphid (Aulacorthum solani)

Adults are yellowish green with long,thin, slightly tapered, dark tipped andflanged siphunculi. The nymphs areshiny green, with a rather bright greenor yellow patch at the base of eachsiphunculus (Figure 6).

Other aphid species

Several other species of aphid canoccasionally be found on strawberry.Acrythosiphon malvae rogersii, amedium sized green aphid with long,flanged siphunculi (honey tubes) oftenoccurs in mixed colonies with thepotato aphid. The violet aphid, Myzusornatus, is occasionally found onstrawberry, more frequently onprotected crops. This species has avery wide host range and is of onlyminor importance on strawberry. Adultsare small, pale brownish or dull greenwith a distinctive dark pattern on thebody. The siphunculi (honeytubes) arepale, moderately long and cylindrical.The head has distinctly convergentprominences, similar to those of theshallot aphid. The black bean aphid,Aphis fabae, is sometimes found insmall colonies. This aphid has a coalblack body (nymphs and adults), adomed head between the antennae(a characteristic of Aphis species) anddistinctive white legs. The strawberryroot aphid, Aphis forbesi, is a smallblue-green aphid which feeds upon bothstrawberry foliage and roots and theyellow rose aphid (Figure 7), Rhodobiumporosum, are common pests ofstrawberry in continental Europe.

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Aphid transmittedvirus diseases

Several aphid-borne viruses infectstrawberry, but the major ones in Europeare strawberry crinkle virus, strawberrymottle virus, strawberry vein bandingvirus and strawberry mild yellow edgevirus. Most strawberry varieties growntoday do not show obvious symptomswhen infected with one of these aphidborne viruses. However, the virusesoften occur in complexes and causedistortion of the plant parts, which mayrender fruit unmarketable.

Since no practical treatments to curevirus-infected plants are available to thegrower, virus diseases of strawberry arepredominantly controlled though the useof virus-free planting material togetherwith control programmes for theirtransmitting agents, particularly aphids.

Strawberry and melon and cottonaphids transmit virus diseases. Thesedifferent virus diseases have differentpersistencies within their aphid vectors

and different acquisition and transmis-sion times and latency periods within theaphid (Table 1). These factors affect therate of spread of the virus and the likelysuccess in limiting virus infection bycontrolling the aphid vectors. Semi-persistent viruses are rapidly acquired bytheir aphid vectors and rapidly spread tonew plants. Aphicides have to control theaphids rapidly and ideally have a strongrepellent and/or anti-feedant effect. Oncea strawberry plant is infested with virus, itremains so for the rest of its life, actingas a source of infection.

Strawberry crinkle virus

Crinkle virus is common in UK strawberrycrops, though many growers have diffi-culty recognising the symptoms. All vari-eties can be infected, but infected plantsmay be symptomless. In sensitivevarieties, leaves may have chloroticspots and leaflets be uneven in size.Distorted, or crinkled, petioles and leavesmay be reduced in size (Figure 8a-b).

The virus is transmitted in a replicative,persistent manner by strawberry aphid.The aphid acquires the virus by feedingon an infected host. The virus replicatesinside the aphid but has a latent periodof 10–19 days under optimal conditions;at lower temperatures the latent periodis longer. Aphids retain strawberrycrinkle virus as long as they live afteracquisition of the virus. A single aphidcan spread the virus to many plants.

Strawberry mottle virus

Strawberry mottle virus is the mostcommon virus of strawberries and ispresent wherever they are grown. Thevirus has numerous strains, which areoften symptomless in strawberryvarieties. Severe strains may cause adecline in vigour and reduce yield by upto 30%. Strawberry mottle virus isvectored in a semi-persistent manner bythe strawberry and the melon and cottonaphids. The virus can be transmitted ina feeding period of a few minutes.

8a Strawberry crinkle virus 8b Strawberry mottle virus

8c Strawberry vein banding virus 8d Strawberry mild yellow edge disease

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Strawberry veinbanding virus

Strawberry vein banding virus is theleast common of the four major aphid-borne virus diseases of strawberry.Three types of symptoms are known tobe caused in sensitive indicator plantsby different strains of strawberry veinbanding virus: vein banding, leaf curland chlorosis. However, most currentlygrown cultivars are symptomless.Mixed infections with crinkle virus cancause serious losses in yield, fruitquality and runner production.Interactions with strawberry mottle ormild yellow edge virus result in milddisease. Strawberry aphid transmitsthe virus in a semi-persistent manner.

An inoculation access period of about30 minutes is required for transmission.Aphicides used to control the aphidvectors and so prevent transmission ofthis virus have to be fast acting or havea good anti-feedant or repellent effect.

Strawberry mild yellowedge disease

Strawberry mild yellow edge is one ofthe most widespread virus diseases ofstrawberry. In the field, the combinationof strawberry mild yellow edge withstrawberry mottle or strawberry crinklevirus causes the disease previouslyknown as yellows. The varietyCambridge Favourite is particularly

susceptible though most modernvarieties are tolerant and do not showsymptoms. The virus is vectored by thestrawberry aphid and related species ina persistent, circulative manner in thefield. Acquisition and inoculation accessperiods lasting overnight or up toseveral days are required for efficienttransmission. Once the virus has beenacquired, the aphid remains infectedwith the virus for most if not all of its life.The virus complex can thus be spreadover considerable distances by aphidvectors transported by air currents.Since strawberry mild yellow edgerequires longer inoculation accessfeeding than the semi-persistentviruses, systemic insecticides haveproven useful in its control.

Table 1 Relative persistencies of aphid transmitted strawberry viruses and their acquisition, transmission andlatency times

Aphid virus vector

Strawberry aphid(Chaetosiphon fragaefolii)

Melon and cotton aphid(Aphis gossypii)

Virus

Crinkle

Mottle

Mild yellow edge

Vein banding

Mottle

Persistencein aphid

Persistent

Semi-persistent

Persistent

Semi-persistent

Semi- or non-persistent

Acquisition by aphid andtransmission to crop times

<24 hours

Minutes/a few hours

Hours/days

Minutes

Minutes/a few hours

Latency period in aphid

10–19 days

None

Days

None

None

Crop damageThe different aphid species cause differenttypes of crop damage. All the speciesdebilitate the plant by sucking sap andexcreting honeydew that contaminatesthe foliage, flowers and fruits. Sootymoulds grow on the honeydew causingblackening. Fruits and/or the calyx maybe contaminated by aphids themselves,their dead bodies or their cast skins. Thedifferent species infest the plants indifferent ways and cause very differentsymptoms of plant distortion.

Strawberry aphid

Strawberry aphids do not distort thefoliage of infested plants but they do makethem sticky with honeydew. This species

is most important as a potential vector ofcrinkle and yellow edge virus diseases.

Shallot aphid

Shallot aphids feed during winter andearly spring, mainly in the growing pointsand young leaves, causing strong plantdistortion symptoms. Infested plantsbecome severely stunted when growthcommences in spring, the petiolesbeing shortened and the leavers curledand twisted (Figure 3). Blossom trusseson infested plants are similarly affected,cropping is much reduced and fruits aresmall and of poor quality. The symptomstend to appear first on individual plantsor in small patches, but damage soonspreads until large areas are affected.Some growers mistake the damage for

that caused by tarsonemid mite (SeeHDC factsheet 15/03).

Potato aphid

Potato aphid causes little direct damageto strawberry. Very heavy infestationsweaken the young shoots and causesome honeydew contamination.

Melon and cotton aphid

Melon and cotton aphids infest foliageand flowers forming dense colonies inpatches which produce copioussecretions of honeydew which rapidlybecome blackened by sooty mould.This aphid can also transmit mottlevirus (see above).

Life cycles

Strawberry aphid

Wingless strawberry aphids breed onstrawberry throughout the year, exceptduring extremely cold winter weather.Populations reach their height insummer. Winged aphids, which spreadinfestations to new plantations, occurin May and June with smaller, lessimportant generations from October toDecember. There is no sexual stage inthe life cycle and eggs are not laid.

Shallot aphid

Winged shallot aphids migrate tostrawberry in the autumn where

colonies of wingless aphids developthroughout the winter and spring.In May or early June, winged formsdevelop which fly to various summerhosts. Colonies on strawberriesdecline and eventually die out.

Potato aphid

Potato aphid can breed on straw-berries all year round under suitableconditions but populations aregreatest on the young foliage in Apriland May when winged formsdevelop which migrate to varioussummer hosts including potato. Smallnumbers of wingless forms mayremain on strawberry throughoutthe summer.

Melon and cotton aphid

Melon and cotton aphid has a very widehost range. It does not have a sexualstage in the UK and no eggs are laid.In warm conditions, the aphid breedscontinuously, winged forms thatmigrate to start new infestations beingproduced at any time in response tocrowding. The aphid breeds rapidly atmoderate to high temperatures but isnot cold-hardy and cannot surviveprolonged periods of sub-zerotemperatures. It does not normallysurvive the winter outdoors in the UK.Infestations in spring and early summerusually originate from a wide range ofglasshouse or protected crops.

Control

Natural enemies

PredatorsAphids are preyed on by a wide rangeof generalist predatory arthropods including; ladybirds, spiders, rovebeetles, lacewing and hoverfly (syrphid)larvae, predatory flower bugs(Anthocoris and Orius sp.) and otherpredatory bugs and anystid mites.

Several studies have shown thatspiders are often the most abundantgroup of predators. Over 20 speciesmay be present. The predatory flowerbug Anthocoris nemorum is one of thecommonest predatory bugs that feedon aphids on strawberry but thesmaller species Orius niger, Oriusmajusculus and Orius laevigatus alsooccur naturally in summer as well asnabid bugs and predatory mirids.Ladybird and lacewing larvae may alsooccur in small to moderate numbers.Other common predators include therove beetles, Tachyporus hypnorumand Tachyporus obtusus, and thepredatory mite Anystis agilis. Manyspecies of ground beetle (carabids)that occur in strawberry fields (somefeed on strawberry fruits) are known tobe predators of aphids in cereal fields.However, their role as predators ofaphids in strawberry crops is largelyunknown. One of the factors likely toinfluence their importance is the extentto which they will climb onto plants toseek prey. Experiments at EMR

showed that some species can climbonto strawberry leaves.

The relatively short life of modernstrawberry plantings counts againstthe establishment of large naturalenemy populations. Also, the practiceof fumigating the ground beforeplanting strawberries is likely todeplete populations of ground-dwelling predators. Many insecticidesused on strawberry are toxic topredators and large naturalpopulations cannot develop wheresuch sprays are used (see below).

Aphid numbers often reachdamaging levels despite the presenceof large numbers of predators. Theincrease in predator numbers often lagsbehind the rapid development of aphidpopulations when weather and plantgrowth conditions are favourable inspring and summer. Because aphids,in particular strawberry aphid, are virusvectors, the numbers of aphids thatcan be tolerated are rather low. Thenatural enemy complex cannot regulatethem consistently to such low levels.Supplementary introductions ofpredatory insects such as predatorymidges (eg Aphidoletes aphidimyza)or lacewing larvae sp. can be madefor biocontrol of aphids in protectedstrawberry crops (see below).

Parasitic waspsMummies of aphids parsitised byparasitic wasps (parasitoids) such asAphelinus and Aphidius sp. are oftennumerous in strawberry crops with

large aphid populations, particularly insummer. Hyperparasites, whichparasitize the parasitoids, may reducetheir effectiveness. Though naturalparasitoid populations and parasitismrates may be high, aphid numbers maystill reach damaging levels.Supplementary introductions of parasiticwasps can be made for biocontrol ofaphids in protected strawberry crops(see below).

Fungi and microbial agentsOutbreaks of the fungal insect pathogenEntomophthora planchoniana occurnaturally in strawberry aphid populations,usually in prolonged periods of moder-ately warm, very humid conditions.Outbreaks are irregular in time andintensity and only occasionally play asignificant part in regulating aphidpopulations. This natural pathogencannot be easily cultured in artificialmedia and therefore cannot currentlybe used as a biocontrol agent, thoughother pathogenic species may offeropportunity (see below).

Enhancing natural enemies

• Persistent, broad-spectruminsecticides, particularly syntheticpyrethroids, are harmful to a widerange of natural enemies and theiruse should be avoided if possible.The best way of increasing naturalenemies is to avoid the use of suchinsecticides and use only selective

insecticides or cultural, biological andbiotechnological control approaches.

• Populations of natural enemies areincreased by providing stablehabitats with a diverse range ofplants around the plantation. Inreality, there is little practicalopportunity of increasing plantdiversity in plantations themselves.

However, the size of plantationsmay be limited and wildlife areasprovided. It should also be notedthat some pests (eg strawberryblossom weevil) use such areasas overwintering sites.

• Successive sowing of flowering herbsin and around the plantation willprovide an alternative food source for

some natural enemies, notablyhoverfly adults, the larvae of whichare predators of aphids. Care inchoice of species is important, asmany flowering plants are hosts tothe European tarnished plant bug,a damaging pest of strawberries atlow population densities (see HDCfactsheet 19/04).

Crop monitoringAs aphids are such common andimportant pests of strawberry, it isimperative that growers familiarisethemselves with the different species,the damage symptoms they causeand how and where to look for them.Crops must be examined carefully andregularly for infestation and damage,including virus infection, as part of theroutine crop-monitoring programme.• It is recommended that each

strawberry field is examined at leastfortnightly, and preferably weekly,for pests and diseases during thegrowing season.

• At the start of each inspection thewhole area should be examinedfrom a high spot in or next to thefield for patches of stunting orabnormal growth or colouring.

• If patches are detected, they shouldbe closely inspected and the causeor causes diagnosed. The causecould be aphids, but there are awide range of other possible causesincluding red core, crown rot,tarsonemid mite, verticillium wilt,vine weevil, waterlogging, etc.

• The crop inspection should becontinued making a zig-zag transectacross the field stopping at aminimum of 10 points per ha.

• At each point, all the plants in a 5 mradius should be overviewed forstunting, distortion, poor growth,honeydew and/or sooty mouldcontamination of foliage or fruits.If present, the particular plant(s)should be closely inspected and thecause diagnosed.

• One plant should be selected atrandom from each of the 10 pointsand closely examined for the signs ofpest or disease infestation or damage.Presence or absence of infestationor damage should be recorded.

• For aphids, it is important to examinethe undersides of the youngestemerging leaves and the undersidesof older leaves. Shallot aphid mayoccur singly or in small numbersbetween the folds of very young,unfurling leaves, which are usuallycharacteristically distorted. Melonand cotton aphid may occur in theflowers. Leaves, flowers and fruits,including stalks, should be examined

for other tell tale signs of aphidinfestation such as a glistening orstickiness of honeydew or thepresence of cast skins. Blackeningby sooty mould usually indicates theinfestation has been present forsome time or at least some time ago.

Unfortunately, economic damagethresholds for the different aphidspests of strawberry have not beendetermined. Simple thresholds that donot take into account time of season,growth stage, crop age, growingconditions and crop value are likely tobe misleading. In general, only verylow populations (< 5% plants infested)of damaging aphid species such asstrawberry aphid or melon and cottonaphid can be tolerated early in theseason. When low levels of thesespecies are found, more frequent(twice weekly) and careful monitoringshould be applied. There is a zerotolerance for shallot aphid. Potatoaphid is less damaging andconsequently higher thresholds apply.

BiocontrolSeveral predators and parasitoidsavailable from biological suppliers canbe used as biocontrol agents ofaphids on strawberry. The most usefulcurrently are the predatory midgeAphidoletes aphidimyza, the parasiticwasps Aphidius colemani andAphidius ervi and larvae of the greenlacewing, Chrysoperla carnea. Anumber of other biocontrol agents arealso available such as the ladybirdAdalia bipunctata, predatory bugs

such Orius and Anthocoris speciesand the entomopathogenic fungusLecanicillium longisporum (formerlynamed Verticillium lecanii), but theseare either at best only partiallyeffective, or expensive or have othersnags or difficulties.• Biocontrol approaches for aphids on

strawberry are only likely to be effec-tive and reliable in protected crops.

• Biocontrol is unsuitable for aphidsin crops for propagation, at least asa stand alone method, because low

populations of aphids can transmitsignificant levels of virus. There isonly a very low tolerance of aphidsin the Plant Health PropagationScheme, nil on high health stocks

• Because of the large number ofaphid species that can occur onstrawberry under protection,biocontrol agents with a broadhost range that can control severalaphid species are preferable tobiocontrol agents that are aphidspecies specific.

Predatory midgeAphidoletes aphidimyza

The predatory midge Aphidoletesaphidimyza is currently the most usefuland effective biocontrol agent for aphidson strawberry (Figure 9). It has a widehost range and can control all the aphidspecies that occur on strawberry. Adultmidges (Figure 10) are mainly active atnight. Females search for aphidcolonies in which to lay their eggs. Thenumber of eggs laid depends on thedensity of the infestation. The midgelarva that hatches is bright orange andimmediately attacks the aphids. Thelarvae inject a poison into an aphid toparalyse it and liquify it internally,making it easier for the larva to consume.When many aphids are available, themidge larvae kill more aphids than theycan consume, making the midge amore effective and reliable predator. Inexperiments at EMR (HDC project SF61) midge larvae consumed a mean of45 young strawberry aphids duringtheir development.

Temperature has a marked effect onthe activity of Aphidoletes aphidimyza;in particular, a minimum dusk and nighttemperature of approx. 14°C is required.This limits the use of Aphidoletes untilabout mid-May at the earliest in tunnels,though may be used prior to this inheated glasshouses. Aphidoletesaphidimyza also needs 15.5 hours ofdaylight per day to prevent it going intodiapause (a state of hibernation) and isonly likely to be fully effective betweenMarch and October, unless there isadequate supplementary lighting. Thediapause switching mechanism actsin the semi-mature larvae. It istherefore possible to use the midgeadults with shorter day lengths earlier inthe season, though the midge will notcomplete its development.

It is recommended that a series ofintroductions (Tables 2) should be madeuntil the midge is well established withpredatory midge larvae present in aphidcolonies and the aphids are effectivelybeing controlled.

Aphidoletes aphidimyza pupates inthe soil and the midge may be lesssuccessful at completing its life cyclewhere the soil or growing medium iscovered with polythene. This mayprevent the midge from establishingand prolong the need for introductions.

Aphidoletes aphidimyza is suppliedas late pupae, often loose in vermiculite

in tubes or pots. The midge typicallycosts approximately £12/1000 at thetime of writing *(2005). The midge needshigh humidity conditions for adultemergence and successful host findingand reproduction. For products fromsome suppliers, the right conditions areclaimed to be provided by the deliverybottle, it being only necessary to removethe cap and place the container withinthe crop. For others, it is recommendedthat special emergence pots are used toprovide the emerging midges with theright conditions. Typically, 15 emergencepots are needed per hectare.

The adult midge is very sensitive toinsecticides, the midge larvae moder-ately so. Use of harmful insecticidesshould be avoided if possible, especiallypersistent ones (see Table 4 & 5).

Sulphur sprays are harmful andcontinuous use of sulphur burners candisrupt host finding by the adult femaleand should be avoided, particularly atdusk when host finding occurs.

Although Aphidoletes aphidimyzaoffers the most promise for biocontrolof the range of aphid species instrawberries, its' reliability andeffectiveness, and safe methods ofintegrating its use with insecticide andfungicide sprays, are largely unprovenin tunnels. In field experiments, wherefour introductions of adult midgeswere made to control strawberryaphid, very few midge larvae werefound in subsequent leaf samples andthere was no effect on aphid numbers(HDC project SF 61). Different releasetechniques need to be investigated.

10 Aphidoletes aphidimyza adult

Average rate of parasitic waspintroduction

0.25/m2/week

0.5–1.0/m2/week

Preventive treatment

Curative treatment of low populations

Preventive treatment

Curative treatment of low populations

Curative treatment of higher populations

Treatment of aphid hot spots

Average rate of predator introduction

0.25/m2/week

0.5–1.0/m2/week

1–2/m2/week

5–10/m2 as a one off introduction

9 Aphidoletes aphidimyza larva predating aphids

Table 2 The recommended rate of Aphidoletes aphidimyza introductiondepends on the density of aphid infestation as follows:

Table 3 Recommended rates of Aphidius ervi or Aphidus colemaniintroduction are:

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Parasitic wasps Aphidius colemani andAphidius ervi

These parasitic wasps lay their eggsinside the aphids body (Figure 11)which turns into a mummy (Figure 12).They are effective but more hostspecific as follows:• Aphidius ervi attacks potato aphid

and glasshouse potato aphid

• Aphidius colemani is effectiveagainst melon and cotton aphid

• No species that is effective againststrawberry aphid that is commerciallyavailable. A naturally occurringparasitoid, Aphidius eglanteriae, isoften found in strawberry plantations,(HDC project SF 61) but numbersgenerally lag behind the populationgrowth of the aphid.

The parasitoids are supplied in aphidmummies, costing about £19 per 250(2005) for Aphidius ervi and less thanhalf that for Aphidius colemani. SeeTable 3 for introduction rates

Parasitic wasp Aphelinusabdominalis

This small parasitic wasp can also beused for biocontrol of aphids onstrawberry. However, it is slower actingand requires higher temperatures thanthe other biocontrol species givenabove. Its effectiveness against the fullrange of aphid species that attackstrawberry is uncertain. This specieswill not parasitise the strawberry aphid(HDC project SF 61).

Predators

Lacewing larvae (Figure 13), such asthe green lacewing Chrysoperlacarnea, have some promise for aphidcontrol in strawberry though theireffectiveness and reliability areinadequately proven. Defra fundedexperiments at EMR showed that alarva consumes up to 800 strawberryaphids during its development.However, releases of 8 larvae perplant were needed to significantlyreduce strawberry aphid numbers infield grown plants. They are moretolerant to low temperatures, and

some chemicals (eg fungicides) thanAphidoletes aphidimyza and theparasitic wasps Aphidius colemaniand A. ervi. Rates of about 10/m2 arenormally used for curative treatment;however a preventative programme atapprox. 1/m2 may have some value,such as in organic crops, but wouldbe relatively expensive (approximately£200/ha/introduction). Introductionswould need to be continued until thepredators are well established and theaphids under control.

Various other predators includingladybirds and predatory bugs such asOrius and Anthocoris are also availablefrom biological suppliers and willpredate aphids in strawberry crops.However, they are costly and their

effectiveness and reliability areunproven. They may be useful in aphidhot spots where rapid control isrequired. In cage experiments to deter-mine the effectiveness of Orius laevi-gatus in reducing strawberry aphidnumbers on potted plants (HDCproject SF 61), a single release of 3and 15 adults (males plus females) persix plants significantly reduced straw-berry aphid numbers four weeks afterrelease. This needs to be validated infield experiments on tunnel grownstrawberries. Multiple releases shouldgive quicker control.

12 Aphidius colemani mummy (right)

11 Aphidius ervi about to parasitise aphid

13 Lacewig larvae consuming aphid

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Chemical controlSeveral insecticides approved for useon strawberry crops are effectiveagainst aphids (Tables 4 & 5) andseveral have a specific labelrecommendation for control of thesepests. Some have harmful effects onbiocontrol agents commonly used instrawberry crops.

Bifenthrin (Talstar):This synthetic pyrethroid insecticideis recommended for control of two-spotted spider mite on strawberry andother crops. It is also approved forcontrol of aphids on many cropsincluding brassicas and cereals.Though it is not specifically recom-mended for aphid control on straw-berries, it is likely to be fairly effectiveagainst aphids with which it comesinto contact. It will not controlresistant strains of the melon andcotton aphid. It acts by contact andresidual action only and is notsystemic or translaminar. It istherefore unlikely to be fully effectiveagainst aphid colonies that areinaccessible to sprays. Control ofshallot aphid is unlikely to besuccessful with this insecticide. Themain drawback of bifenthrin is that itis a broad-spectrum insecticide withpersistent harmful effects againstmany biocontrol agents and naturalenemies including the predatory mitesPhytoseiulus persimilis andAmblyseius cucumeris, and all thebiocontrol agents for aphidsdescribed above.

Chlorpyrifos (Lorsban, Equity etc):This moderately persistentorganophosphorus insecticide is fairlyeffective against aphids. It is oftenused on strawberries before floweringfor control of several pests includingblossom weevil, caterpillars andaphids. It will not control resistantstrains of the melon and cotton aphid.It has moderately long (6–8 weeks)harmful effects on the predatory miteAmblyseius cucumeris which isfrequently used for biocontrol oftarsonemid mite and thrips instrawberry crops. It is also harmful tonatural enemies and all the biocontrolagents for aphids described above.

Nicotine (XL-All Nicotine etc): Nicotine is approved for control of

aphids on soft fruit and many othercrops including strawberries. It ismoderately effective, though seldomused because of its short persistence,toxicity to humans (including throughskin contact) and the need to wear arespirator when applying sprays. Itsmain use on strawberries is for controlof resistant strains of the melon andcotton aphid, which are difficult tocontrol with most other aphicides.It has short-term harmful effects topredatory mites.

Thiacloprid (Calypso): This systemic nicotinyl insecticide isapproved for control of rosy appleaphid on apple and has Specific Off-label Approvals (SOLAs) for use onseveral other crops including outdoorstrawberries (Notice of Approvalnumber 2727/2003) and protectedstrawberries (Notice of Approvalnumber 1497/2004). It will controlresistant strains of the cotton-melonaphid. Calypso is moderately harmfulto the predatory mites used asbiocontrol agents and very harmful toOrius predatory bugs.

Pirimicarb (Aphox): This partially systemic carbamateaphicide is approved for control ofaphids on strawberry and many othercrops. It works best in warmerconditions. It is effective for most ofthe aphid species that occur onstrawberry though it will not controlresistant strains of the melon andcotton aphid. It is a selectiveinsecticide and is safe to most naturalenemies and biocontrol agentsthough it is reported to have limited,short term harmful effects onAmblyseius cucumeris (Tables 4 & 5).It has a 3-day harvest interval onstrawberries. Note that pirimicarb isan anticholinesterase compound.

Pymetrozine(Chess WG, Plenum WG):This systemic insecticide is approvedfor control of aphids on ornamentals,protected cucumbers and potatoesand now has a Specific Off-labelApprovals (SOLA’s), 1072/2003(Chess WG) and 1073/2003 (PlenumWG), for use in strawberry, cane fruitand currants. However, the 12 weekharvest interval will often preclude itsuse in fruiting strawberry crops, asevere limitation. It acts mainly as an

aphid anti-feedant. Feeding normallystops within minutes of application.Then aphids starve to death. This maytake a few hours in summer but maytake several days in cold winterconditions. Note that on strawberry,Chess is only approved for use inprotected crops and Plenum WG isonly approved for use in outdoorcrops. Pymetrozine is likely to beeffective against aphids on strawberryThe main advantage of this product isthat is comparatively safe to naturalenemies and biocontrol agents,including the predatory midgeAphidoletes aphidimyza. It is also safeto bumble bees.

Activeingredient

bifenthrin

chlorpyrifos

nicotine

pirimicarb

pymetrozine

thiacloprid

Trade name(examples)

Talstar

Lorsban, Equity etc

XL All 95%nicotine

Aphox

Chess WG*Plenum WG*

Calypso

Class

pyrethroid

OP

alkaloid

carbamate

azomethine

chloronicotinyl

Persistence

long

long

short

short

moderate

long

Pest

Two-spotted spider mitein strawberries and othercrops. Aphids in brassicas,cereals and hops.

Aphids, caterpillars, spidermites, blossom weevil,vine weevil in strawberries.

Aphids, capsids,leafhoppers, sawflies in soft fruit and other crops

Aphids in strawberriesand many other crops

SOLA (no label recommen-dations) for aphid controlin strawberries. Approvedfor control of aphids inmany other crops

SOLA on outdoor &protected strawberry forcapsid control until Dec 05.Rosy apple aphid in apple.

Likely efficacy

Moderate

Good exceptagainst resistantmelon-cotton aphid

Good and shouldcontrol resistant melonand cotton aphid

Good except againstresistant melon andcotton aphid

Good

Good

Phytoseiulus

h, 8–12 wks

mh, 0.5 wks

h, 1 wk

s

sh

mh

Amblyseiuscucumeris

h, 8–12 wks

h, 6–8 wks

h, 1 wk

mh, 3 wks

s

?

Amblyseiuscalifornicus

s

mh, 2 wks

?

s

s

?

Aphidoletesaphidimyza

h, 8–12 wks

h, ? wks

h, 0 wks

s, larvaeh, adults1 wk

?

?

Aphidiuservi/colemani

h, 8–12 wks

h, ? wks

?

s

s, mummymh, adults1/2 wk

mhadults? wks

Approval (label recommendation)

Choice of insecticides - Efficacy factors

Safety to biocontrol agents

h harmful mh moderately harmful s safe sh slightly harmful

* Chess WG has a SOLA for use on protected crops only, Plenum WG has a SOLA for use on outdoor crops only

Table 4 Insecticides approved for use on strawberry that are recommended or likely to be effective, at least partially, for control of aphids

December 2005

Whilst publications issued under the auspices

of the HDC are prepared from the best available

information, neither the authors or the HDC can

accept any responsibility for inaccuracy or

liability for loss, damage or injury from the appli-

cation of any concept or procedure discussed.

© 2005 Horticultural Development Council.

No part of this publication may be reproduced in

any form or by any means without prior permis-

sion of the Horticultural Development Council.

Design and production: HDR Visual Communication

bifenthrin

chlorpyrifos

nicotine

pirimicarb

pymetrozine

thiacloprid

Hazards

Anticholin-esterase?

no

yes

no

yes

no

no

Humans

h, i

h, i

t

t, h

u

h

Fish & otheraquatic life

ed

ed

d

vt

h

h

Bees

ed

d

h

le

hr

u

Harvest interval(days)

0

14

2

3

12 weeks

3

Maximum number of sprays

2 per year

3 per year

u

u

3 per crop

Maximum total dose500ml product per year

Buffer zonewidth (m)*

18

18

u

u

u

30

h harmful

i irritant

d dangerous

ed extremely dangerous

hr high risk

le has little effect

u uncategorised/unclassified/unspecified

vt very toxic

t toxic

* buffer zone distances are for broadcast

air-assisted sprayers

Glossary of terms:Acquisition:Period of feeding needed for theaphid to ingest or 'acquire' the virus

Circulative:Virus remains and reproduces withinthe aphid gut system

Inoculation access period:Period of feeding for the aphid topass the virus in to the plant

Latency period:Time between aphid ingesting the virusand it then becoming established in theaphid gut system for subsequentinfection to a host plant

Persistent:Remaining within the aphid gut system

Replicative:Virus particles replicate (ie increase innumber) within the aphid vector's bodyandarenot justcarriedon themouthparts

Semi-persistent:A virus that does not permanently infectthe aphid vector, requires long periodsof feeding to acquire, and many hoursto successfully transmit. Note thatstrawberry plants once infected withviruses are permanently infected.

Transmission:To pass on the virus to the plant

Table 5 Hazards, harvest intervals and spray information for insecticides approved for use on strawberry