Factsheet 26/05 Horticultural Bradbourne House Development East Malling Council Kent ME19 6DZ T: 01732 848383 F: 01732 848498 Project No. SF 61 E: [email protected]

Aphids and their control on strawberry

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

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

Pest identification

Several species of aphid are commonly found on strawberry in the UK. Straw- berry aphid, shallot aphid, potato aphid and the melon and cotton aphid are the most common, but many other species occur occasionally. Glasshouse and potato aphid is common under protection. The different aphid species cause different types of damage and require different control approaches. For this reason, it is important to identify which species are present and their relative incidence. The different species are fairly easy to recognise by their appear- ance, distribution on the plant and the damage they cause. Close examination with a hand lens may sometimes be required for identification with certainty.

Strawberry aphid 1 Strawberry aphid (close up above and colony below) ( fragaefolii)

Adults are small, whitish green with Diagram 1 red eyes and their bodies are sparsely clothed with capitate body hairs (Figure 1, Diagram 1). Siphunculi (honey tubes) are moderately long. They are usually found on the undersides of leaves and, when infestations are heavy, on leaf petioles.

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 to black, with younger individuals in a family group characteristically being lighter and more mature individuals darker (Figure 2). The legs are lighter, but not uniformly white (see black bean aphid (Aphis fabae) below), and in common with other Aphis species, melon and cotton aphids have a 2 Melon and cotton aphid (Aphis gossypii) adult, Ieft; aphids in strawberry flower, right domed head between the antennae. The aphid forms dense colonies that secrete honeydew copiously. This species is often resistant and survives treatment with many aphicides.

Shallot aphid (Myzus ascalonicus)

Adults are small, pale brown or yellowish or greenish brown (Figure 3). The front of the head is emarginate (convex) between the antennae and 3 Shallot aphid prominences are slightly convergent (Diagram 2). Siphunculi (honey tubes) are distinctly swollen towards the tip (Diagram 2). This aphid is mainly found in the growing points of plants, often in small numbers and can be difficult to find. However, unlike the other aphids that feed on strawberry, shallot aphid causes noticeable stunting of the growth and characteristic twisting of leaves (Figure 4).

4 Shallot aphid damage to strawberry

Diagram 2

Shallot aphid showing siphunculus (honeytube) which is distinctly swollen towards the tip and the prominences on the forehead below the base of the antennae. Potato aphid (Macrosiphum euphorbiae)

Adults are large, with individuals in a colony ranging from yellowish-green to pink. Siphunculi (honeytubes), are very long, cylindrical and sometimes dark tipped (Figure 5).

Glasshouse and potato aphid (Aulacorthum solani)

Adults are yellowish green with long, thin, slightly tapered, dark tipped and flanged siphunculi. The nymphs are shiny green, with a rather bright green or yellow patch at the base of each siphunculus (Figure 6). 5 Potato aphid on strawberry leaf

Other aphid species

Several other species of aphid can occasionally be found on strawberry. Acrythosiphon malvae rogersii,a medium sized green aphid with long, flanged siphunculi (honey tubes) often occurs in mixed colonies with the potato aphid. The violet aphid, Myzus ornatus, is occasionally found on strawberry, more frequently on protected crops. This species has a very wide host range and is of only minor importance on strawberry. Adults are small, pale brownish or dull green with a distinctive dark pattern on the body. The siphunculi (honeytubes) are pale, moderately long and cylindrical. The head has distinctly convergent 6 Glasshouse and potato aphid prominences, similar to those of the shallot aphid. The black bean aphid, Aphis fabae, is sometimes found in small colonies. This aphid has a coal black body (nymphs and adults), a domed head between the antennae (a characteristic of Aphis species) and distinctive white legs. The strawberry root aphid, Aphis forbesi, is a small blue-green aphid which feeds upon both strawberry foliage and roots and the yellow rose aphid (Figure 7), Rhodobium porosum, are common pests of strawberry in continental Europe. Photo courtesy of J.L. Castner & University Florida

7 Yellow rose aphid Aphid transmitted and different acquisition and transmis- The virus is transmitted in a replicative, sion times and latency periods within the persistent manner by strawberry aphid. virus diseases aphid (Table 1). These factors affect the The aphid acquires the virus by feeding rate of spread of the virus and the likely on an infected host. The virus replicates Several aphid-borne viruses infect success in limiting virus infection by inside the aphid but has a latent period strawberry, but the major ones in Europe controlling the aphid vectors. Semi- of 10–19 days under optimal conditions; are strawberry crinkle virus, strawberry persistent viruses are rapidly acquired by at lower temperatures the latent period mottle virus, strawberry vein banding their aphid vectors and rapidly spread to is longer. Aphids retain strawberry virus and strawberry mild yellow edge new plants. Aphicides have to control the crinkle virus as long as they live after virus. Most strawberry varieties grown aphids rapidly and ideally have a strong acquisition of the virus. A single aphid today do not show obvious symptoms repellent and/or anti-feedant effect. Once can spread the virus to many plants. when infected with one of these aphid a strawberry plant is infested with virus, it borne viruses. However, the viruses remains so for the rest of its life, acting often occur in complexes and cause as a source of infection. Strawberry mottle virus distortion of the plant parts, which may render fruit unmarketable. Strawberry mottle virus is the most Since no practical treatments to cure Strawberry crinkle virus common virus of strawberries and is virus-infected plants are available to the present wherever they are grown. The grower, virus diseases of strawberry are Crinkle virus is common in UK strawberry virus has numerous strains, which are predominantly controlled though the use crops, though many growers have diffi- often symptomless in strawberry of virus-free planting material together culty recognising the symptoms. All vari- varieties. Severe strains may cause a with control programmes for their eties can be infected, but infected plants decline in vigour and reduce yield by up transmitting agents, particularly aphids. may be symptomless. In sensitive to 30%. Strawberry mottle virus is Strawberry and melon and cotton varieties, leaves may have chlorotic vectored in a semi-persistent manner by aphids transmit virus diseases. These spots and leaflets be uneven in size. the strawberry and the melon and cotton different virus diseases have different Distorted, or crinkled, petioles and leaves aphids. The virus can be transmitted in persistencies within their aphid vectors may be reduced in size (Figure 8a-b). a feeding period of a few minutes. Photo courtesy of Horst, NL Centre, Jongedijk, Naktuinbouw Test Gerard Photo courtesy of Horst, NL Centre, Jongedijk, Naktuinbouw Test Gerard

8a Strawberry crinkle virus 8b Strawberry mottle virus Photo courtesy of Horst, NL Centre, Jongedijk, Naktuinbouw Test Gerard Photo courtesy of Horst, NL Centre, Jongedijk, Naktuinbouw Test Gerard

8c Strawberry vein banding virus 8d Strawberry mild yellow edge disease Strawberry vein An inoculation access period of about susceptible though most modern banding virus 30 minutes is required for transmission. varieties are tolerant and do not show Aphicides used to control the aphid symptoms. The virus is vectored by the Strawberry vein banding virus is the vectors and so prevent transmission of strawberry aphid and related species in least common of the four major aphid- this virus have to be fast acting or have a persistent, circulative manner in the borne virus diseases of strawberry. a good anti-feedant or repellent effect. field. Acquisition and inoculation access Three types of symptoms are known to periods lasting overnight or up to be caused in sensitive indicator plants several days are required for efficient by different strains of strawberry vein Strawberry mild yellow transmission. Once the virus has been banding virus: vein banding, leaf curl edge disease acquired, the aphid remains infected and chlorosis. However, most currently with the virus for most if not all of its life. grown cultivars are symptomless. Strawberry mild yellow edge is one of The virus complex can thus be spread Mixed infections with crinkle virus can the most widespread virus diseases of over considerable distances by aphid cause serious losses in yield, fruit strawberry. In the field, the combination vectors transported by air currents. quality and runner production. of strawberry mild yellow edge with Since strawberry mild yellow edge Interactions with strawberry mottle or strawberry mottle or strawberry crinkle requires longer inoculation access mild yellow edge virus result in mild virus causes the disease previously feeding than the semi-persistent disease. Strawberry aphid transmits known as yellows. The variety viruses, systemic insecticides have the virus in a semi-persistent manner. Cambridge Favourite is particularly proven useful in its control.

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

Aphid virus vector Virus Persistence Acquisition by aphid and Latency period in aphid transmission to crop times in aphid

Strawberry aphid Crinkle Persistent <24 hours 10–19 days (Chaetosiphon fragaefolii) Mottle Semi-persistent Minutes/a few hours None

Mild yellow edge Persistent Hours/days Days

Vein banding Semi-persistent Minutes None

Melon and cotton aphid Mottle Semi- or non- Minutes/a few hours None (Aphis gossypii) persistent

Crop damage is most important as a potential vector of that caused by tarsonemid mite (See crinkle and yellow edge virus diseases. HDC factsheet 15/03). The different aphid species cause different types of crop damage. All the species debilitate the plant by sucking sap and Shallot aphid Potato aphid excreting honeydew that contaminates the foliage, flowers and fruits. Sooty Shallot aphids feed during winter and Potato aphid causes little direct damage moulds grow on the honeydew causing early spring, mainly in the growing points to strawberry. Very heavy infestations blackening. Fruits and/or the calyx may and young leaves, causing strong plant weaken the young shoots and cause be contaminated by aphids themselves, distortion symptoms. Infested plants some honeydew contamination. their dead bodies or their cast skins. The become severely stunted when growth different species infest the plants in commences in spring, the petioles different ways and cause very different being shortened and the leavers curled Melon and cotton aphid symptoms of plant distortion. and twisted (Figure 3). Blossom trusses on infested plants are similarly affected, Melon and cotton aphids infest foliage cropping is much reduced and fruits are and flowers forming dense colonies in Strawberry aphid small and of poor quality. The symptoms patches which produce copious tend to appear first on individual plants secretions of honeydew which rapidly Strawberry aphids do not distort the or in small patches, but damage soon become blackened by sooty mould. foliage of infested plants but they do make spreads until large areas are affected. This aphid can also transmit mottle them sticky with honeydew. This species Some growers mistake the damage for virus (see above). Life cycles colonies of wingless aphids develop Melon and cotton aphid throughout the winter and spring. Strawberry aphid In May or early June, winged forms Melon and cotton aphid has a very wide develop which fly to various summer host range. It does not have a sexual Wingless strawberry aphids breed on hosts. Colonies on strawberries stage in the UK and no eggs are laid. strawberry throughout the year, except decline and eventually die out. In warm conditions, the aphid breeds during extremely cold winter weather. continuously, winged forms that Populations reach their height in migrate to start new infestations being summer. Winged aphids, which spread Potato aphid produced at any time in response to infestations to new plantations, occur crowding. The aphid breeds rapidly at in May and June with smaller, less Potato aphid can breed on straw- moderate to high temperatures but is important generations from October to berries all year round under suitable not cold-hardy and cannot survive December. There is no sexual stage in conditions but populations are prolonged periods of sub-zero the life cycle and eggs are not laid. greatest on the young foliage in April temperatures. It does not normally and May when winged forms survive the winter outdoors in the UK. develop which migrate to various Infestations in spring and early summer Shallot aphid summer hosts including potato. Small usually originate from a wide range of numbers of wingless forms may glasshouse or protected crops. Winged shallot aphids migrate to remain on strawberry throughout strawberry in the autumn where the summer.

Control showed that some species can climb large aphid populations, particularly in onto strawberry leaves. summer. Hyperparasites, which Natural enemies The relatively short life of modern parasitize the parasitoids, may reduce strawberry plantings counts against their effectiveness. Though natural Predators the establishment of large natural parasitoid populations and parasitism Aphids are preyed on by a wide range enemy populations. Also, the practice rates may be high, aphid numbers may of generalist predatory of fumigating the ground before still reach damaging levels. including; ladybirds, spiders, rove planting strawberries is likely to Supplementary introductions of parasitic beetles, lacewing and hoverfly (syrphid) deplete populations of ground- wasps can be made for biocontrol of larvae, predatory flower bugs dwelling predators. Many insecticides aphids in protected strawberry crops (Anthocoris and Orius sp.) and other used on strawberry are toxic to (see below). predatory bugs and anystid mites. predators and large natural Several studies have shown that populations cannot develop where Fungi and microbial agents spiders are often the most abundant such sprays are used (see below). Outbreaks of the fungal pathogen group of predators. Over 20 species Aphid numbers often reach Entomophthora planchoniana occur may be present. The predatory flower damaging levels despite the presence naturally in strawberry aphid populations, bug Anthocoris nemorum is one of the of large numbers of predators. The usually in prolonged periods of moder- commonest predatory bugs that feed increase in predator numbers often lags ately warm, very humid conditions. on aphids on strawberry but the behind the rapid development of aphid Outbreaks are irregular in time and smaller species Orius niger, Orius populations when weather and plant intensity and only occasionally play a majusculus and Orius laevigatus also growth conditions are favourable in significant part in regulating aphid occur naturally in summer as well as spring and summer. Because aphids, populations. This natural pathogen nabid bugs and predatory mirids. in particular strawberry aphid, are virus cannot be easily cultured in artificial Ladybird and lacewing larvae may also vectors, the numbers of aphids that media and therefore cannot currently occur in small to moderate numbers. can be tolerated are rather low. The be used as a biocontrol agent, though Other common predators include the natural enemy complex cannot regulate other pathogenic species may offer rove beetles, Tachyporus hypnorum them consistently to such low levels. opportunity (see below). and Tachyporus obtusus, and the Supplementary introductions of predatory mite Anystis agilis. Many predatory such as predatory species of ground beetle (carabids) midges (eg Aphidoletes aphidimyza) Enhancing natural enemies that occur in strawberry fields (some or lacewing larvae sp. can be made feed on strawberry fruits) are known to for biocontrol of aphids in protected • Persistent, broad-spectrum be predators of aphids in cereal fields. strawberry crops (see below). insecticides, particularly synthetic However, their role as predators of pyrethroids, are harmful to a wide aphids in strawberry crops is largely Parasitic wasps range of natural enemies and their unknown. One of the factors likely to Mummies of aphids parsitised by use should be avoided if possible. influence their importance is the extent parasitic wasps (parasitoids) such as The best way of increasing natural to which they will climb onto plants to Aphelinus and Aphidius sp. are often enemies is to avoid the use of such seek prey. Experiments at EMR numerous in strawberry crops with insecticides and use only selective insecticides or cultural, biological and However, the size of plantations some natural enemies, notably biotechnological control approaches. may be limited and wildlife areas hoverfly adults, the larvae of which provided. It should also be noted are predators of aphids. Care in • Populations of natural enemies are that some pests (eg strawberry choice of species is important, as increased by providing stable blossom weevil) use such areas many flowering plants are hosts to habitats with a diverse range of as overwintering sites. the European tarnished plant bug, plants around the plantation. In a damaging pest of strawberries at reality, there is little practical • Successive sowing of flowering herbs low population densities (see HDC opportunity of increasing plant in and around the plantation will factsheet 19/04). diversity in plantations themselves. provide an alternative food source for

Crop monitoring • The crop inspection should be for other tell tale signs of aphid continued making a zig-zag transect infestation such as a glistening or As aphids are such common and across the field stopping at a stickiness of honeydew or the important pests of strawberry, it is minimum of 10 points per ha. presence of cast skins. Blackening imperative that growers familiarise by sooty mould usually indicates the themselves with the different species, • At each point, all the plants in a 5 m infestation has been present for the damage symptoms they cause radius should be overviewed for some time or at least some time ago. and how and where to look for them. stunting, distortion, poor growth, Crops must be examined carefully and honeydew and/or sooty mould Unfortunately, economic damage regularly for infestation and damage, contamination of foliage or fruits. thresholds for the different aphids including virus infection, as part of the If present, the particular plant(s) pests of strawberry have not been routine crop-monitoring programme. should be closely inspected and the determined. Simple thresholds that do • It is recommended that each cause diagnosed. not take into account time of season, strawberry field is examined at least growth stage, crop age, growing fortnightly, and preferably weekly, • One plant should be selected at conditions and crop value are likely to for pests and diseases during the random from each of the 10 points be misleading. In general, only very growing season. and closely examined for the signs of low populations (< 5% plants infested) pest or disease infestation or damage. of damaging aphid species such as • At the start of each inspection the Presence or absence of infestation strawberry aphid or melon and cotton whole area should be examined or damage should be recorded. aphid can be tolerated early in the from a high spot in or next to the season. When low levels of these field for patches of stunting or • For aphids, it is important to examine species are found, more frequent abnormal growth or colouring. the undersides of the youngest (twice weekly) and careful monitoring emerging leaves and the undersides should be applied. There is a zero • If patches are detected, they should of older leaves. Shallot aphid may tolerance for shallot aphid. Potato be closely inspected and the cause occur singly or in small numbers aphid is less damaging and or causes diagnosed. The cause between the folds of very young, consequently higher thresholds apply. could be aphids, but there are a unfurling leaves, which are usually wide range of other possible causes characteristically distorted. Melon including red core, crown rot, and cotton aphid may occur in the tarsonemid mite, verticillium wilt, flowers. Leaves, flowers and fruits, vine weevil, waterlogging, etc. including stalks, should be examined

Biocontrol such Orius and Anthocoris species populations of aphids can transmit and the entomopathogenic fungus significant levels of virus. There is Several predators and parasitoids Lecanicillium longisporum (formerly only a very low tolerance of aphids available from biological suppliers can named Verticillium lecanii), but these in the Plant Health Propagation be used as biocontrol agents of are either at best only partially Scheme, nil on high health stocks aphids on strawberry. The most useful effective, or expensive or have other currently are the predatory midge snags or difficulties. • Because of the large number of Aphidoletes aphidimyza, the parasitic • Biocontrol approaches for aphids on aphid species that can occur on wasps Aphidius colemani and strawberry are only likely to be effec- strawberry under protection, Aphidius ervi and larvae of the green tive and reliable in protected crops. biocontrol agents with a broad lacewing, Chrysoperla carnea. A host range that can control several number of other biocontrol agents are • Biocontrol is unsuitable for aphids aphid species are preferable to also available such as the ladybird in crops for propagation, at least as biocontrol agents that are aphid Adalia bipunctata, predatory bugs a stand alone method, because low species specific. Predatory midge in tubes or pots. The midge typically Sulphur sprays are harmful and Aphidoletes aphidimyza costs approximately £12/1000 at the continuous use of sulphur burners can time of writing *(2005). The midge needs disrupt host finding by the adult female The predatory midge Aphidoletes high humidity conditions for adult and should be avoided, particularly at aphidimyza is currently the most useful emergence and successful host finding dusk when host finding occurs. and effective biocontrol agent for aphids and reproduction. For products from Although Aphidoletes aphidimyza on strawberry (Figure 9). It has a wide some suppliers, the right conditions are offers the most promise for biocontrol host range and can control all the aphid claimed to be provided by the delivery of the range of aphid species in species that occur on strawberry. Adult bottle, it being only necessary to remove strawberries, its' reliability and midges (Figure 10) are mainly active at the cap and place the container within effectiveness, and safe methods of night. Females search for aphid the crop. For others, it is recommended integrating its use with insecticide and colonies in which to lay their eggs. The that special emergence pots are used to fungicide sprays, are largely unproven number of eggs laid depends on the provide the emerging midges with the in tunnels. In field experiments, where density of the infestation. The midge right conditions. Typically, 15 emergence four introductions of adult midges larva that hatches is bright orange and pots are needed per hectare. were made to control strawberry immediately attacks the aphids. The The adult midge is very sensitive to aphid, very few midge larvae were larvae inject a poison into an aphid to insecticides, the midge larvae moder- found in subsequent leaf samples and paralyse it and liquify it internally, ately so. Use of harmful insecticides there was no effect on aphid numbers making it easier for the larva to consume. should be avoided if possible, especially (HDC project SF 61). Different release When many aphids are available, the persistent ones (see Table 4 & 5). techniques need to be investigated. midge larvae kill more aphids than they can consume, making the midge a more effective and reliable predator. In Table 2 The recommended rate of Aphidoletes aphidimyza introduction experiments at EMR (HDC project SF depends on the density of aphid infestation as follows: 61) midge larvae consumed a mean of 45 young strawberry aphids during Average rate of their development. predator introduction Temperature has a marked effect on the activity of Aphidoletes aphidimyza; Preventive treatment 0.25/m2/week in particular, a minimum dusk and night temperature of approx. 14°C is required. Curative treatment of low populations 0.5–1.0/m2/week This limits the use of Aphidoletes until about mid-May at the earliest in tunnels, Curative treatment of higher populations 1–2/m2/week though may be used prior to this in heated glasshouses. Aphidoletes Treatment of aphid hot spots 5–10/m2 as a one off introduction aphidimyza also needs 15.5 hours of daylight per day to prevent it going into diapause (a state of hibernation) and is only likely to be fully effective between Table 3 Recommended rates of Aphidius ervi or Aphidus colemani March and October, unless there is introduction are: adequate supplementary lighting. The diapause switching mechanism acts Average rate of parasitic wasp in the semi-mature larvae. It is introduction therefore possible to use the midge adults with shorter day lengths earlier in Preventive treatment 0.25/m2/week the season, though the midge will not complete its development. Curative treatment of low populations 0.5–1.0/m2/week It is recommended that a series of introductions (Tables 2) should be made until the midge is well established with predatory midge larvae present in aphid colonies and the aphids are effectively being controlled. Aphidoletes aphidimyza pupates in the soil and the midge may be less successful at completing its life cycle where the soil or growing medium is covered with polythene. This may prevent the midge from establishing and prolong the need for introductions. Photo courtesy of Bob Knight, Koppert Aphidoletes aphidimyza is supplied Photo courtesy of Bob Knight, Koppert as late pupae, often loose in vermiculite 9 Aphidoletes aphidimyza larva predating aphids 10 Aphidoletes aphidimyza adult Parasitic wasps some chemicals (eg fungicides) than effectiveness and reliability are Aphidius colemani and Aphidoletes aphidimyza and the unproven. They may be useful in aphid Aphidius ervi parasitic wasps Aphidius colemani hot spots where rapid control is and A. ervi. Rates of about 10/m2 are required. In cage experiments to deter- These parasitic wasps lay their eggs normally used for curative treatment; mine the effectiveness of Orius laevi- inside the aphids body (Figure 11) however a preventative programme at gatus in reducing strawberry aphid which turns into a mummy (Figure 12). approx. 1/m2 may have some value, numbers on potted plants (HDC They are effective but more host such as in organic crops, but would project SF 61), a single release of 3 specific as follows: be relatively expensive (approximately and 15 adults (males plus females) per • Aphidius ervi attacks potato aphid £200/ha/introduction). Introductions six plants significantly reduced straw- and glasshouse potato aphid would need to be continued until the berry aphid numbers four weeks after predators are well established and the release. This needs to be validated in • Aphidius colemani is effective aphids under control. field experiments on tunnel grown against melon and cotton aphid Various other predators including strawberries. Multiple releases should ladybirds and predatory bugs such as give quicker control. • No species that is effective against Orius and Anthocoris are also available strawberry aphid that is commercially from biological suppliers and will available. A naturally occurring predate aphids in strawberry crops. parasitoid, Aphidius eglanteriae, is However, they are costly and their often found in strawberry plantations, (HDC project SF 61) but numbers generally lag behind the population growth of the aphid.

The parasitoids are supplied in aphid mummies, costing about £19 per 250 (2005) for Aphidius ervi and less than half that for Aphidius colemani. See Table 3 for introduction rates

Parasitic wasp Aphelinus abdominalis 11 Aphidius ervi about to parasitise aphid This small parasitic wasp can also be used for biocontrol of aphids on strawberry. However, it is slower acting and requires higher temperatures than the other biocontrol species given above. Its effectiveness against the full range of aphid species that attack strawberry is uncertain. This species will not parasitise the strawberry aphid (HDC project SF 61).

Predators Photo courtesy of Bob Knight, Koppert 12 Aphidius colemani mummy (right) Lacewing larvae (Figure 13), such as the green lacewing Chrysoperla carnea, have some promise for aphid control in strawberry though their effectiveness and reliability are inadequately proven. Defra funded experiments at EMR showed that a larva consumes up to 800 strawberry aphids during its development. However, releases of 8 larvae per plant were needed to significantly reduce strawberry aphid numbers in field grown plants. They are more tolerant to low temperatures, and 13 Lacewig larvae consuming aphid Chemical control aphids on soft fruit and many other aphid anti-feedant. Feeding normally crops including strawberries. It is stops within minutes of application. Several insecticides approved for use moderately effective, though seldom Then aphids starve to death. This may on strawberry crops are effective used because of its short persistence, take a few hours in summer but may against aphids (Tables 4 & 5) and toxicity to humans (including through take several days in cold winter several have a specific label skin contact) and the need to wear a conditions. Note that on strawberry, recommendation for control of these respirator when applying sprays. Its Chess is only approved for use in pests. Some have harmful effects on main use on strawberries is for control protected crops and Plenum WG is biocontrol agents commonly used in of resistant strains of the melon and only approved for use in outdoor strawberry crops. cotton aphid, which are difficult to crops. Pymetrozine is likely to be control with most other aphicides. effective against aphids on strawberry Bifenthrin (Talstar): It has short-term harmful effects to The main advantage of this product is This synthetic pyrethroid insecticide predatory mites. that is comparatively safe to natural is recommended for control of two- enemies and biocontrol agents, spotted spider mite on strawberry and Thiacloprid (Calypso): including the predatory midge other crops. It is also approved for This systemic nicotinyl insecticide is Aphidoletes aphidimyza. It is also safe control of aphids on many crops approved for control of rosy apple to bumble bees. including brassicas and cereals. aphid on apple and has Specific Off- Though it is not specifically recom- label Approvals (SOLAs) for use on mended for aphid control on straw- several other crops including outdoor berries, it is likely to be fairly effective strawberries (Notice of Approval against aphids with which it comes number 2727/2003) and protected into contact. It will not control strawberries (Notice of Approval resistant strains of the melon and number 1497/2004). It will control cotton aphid. It acts by contact and resistant strains of the cotton-melon residual action only and is not aphid. Calypso is moderately harmful systemic or translaminar. It is to the predatory mites used as therefore unlikely to be fully effective biocontrol agents and very harmful to against aphid colonies that are Orius predatory bugs. inaccessible to sprays. Control of shallot aphid is unlikely to be Pirimicarb (Aphox): successful with this insecticide. The This partially systemic carbamate main drawback of bifenthrin is that it aphicide is approved for control of is a broad-spectrum insecticide with aphids on strawberry and many other persistent harmful effects against crops. It works best in warmer many biocontrol agents and natural conditions. It is effective for most of enemies including the predatory mites the aphid species that occur on Phytoseiulus persimilis and strawberry though it will not control Amblyseius cucumeris, and all the resistant strains of the melon and biocontrol agents for aphids cotton aphid. It is a selective described above. insecticide and is safe to most natural enemies and biocontrol agents Chlorpyrifos (Lorsban, Equity etc): though it is reported to have limited, This moderately persistent short term harmful effects on organophosphorus insecticide is fairly Amblyseius cucumeris (Tables 4 & 5). effective against aphids. It is often It has a 3-day harvest interval on used on strawberries before flowering strawberries. Note that pirimicarb is for control of several pests including an anticholinesterase compound. blossom weevil, caterpillars and aphids. It will not control resistant Pymetrozine strains of the melon and cotton aphid. (Chess WG, Plenum WG): It has moderately long (6–8 weeks) This systemic insecticide is approved harmful effects on the predatory mite for control of aphids on ornamentals, Amblyseius cucumeris which is protected cucumbers and potatoes frequently used for biocontrol of and now has a Specific Off-label tarsonemid mite and thrips in Approvals (SOLA’s), 1072/2003 strawberry crops. It is also harmful to (Chess WG) and 1073/2003 (Plenum natural enemies and all the biocontrol WG), for use in strawberry, cane fruit agents for aphids described above. and currants. However, the 12 week harvest interval will often preclude its Nicotine (XL-All Nicotine etc): use in fruiting strawberry crops, a Nicotine is approved for control of severe limitation. It acts mainly as an Table 4 Insecticides approved for use on strawberry that are recommended or likely to be effective, at least partially, for control of aphids

Choice of insecticides - Efficacy factors

Active Trade name Class Persistence Approval (label recommendation) Safety to biocontrol agents ingredient (examples)

Pest Likely efficacy Phytoseiulus Amblyseius Amblyseius Aphidoletes Aphidius cucumeris californicus aphidimyza ervi/colemani

bifenthrin Talstar pyrethroid long Two-spotted spider mite Moderate h, 8–12 wks h, 8–12 wks s h, 8–12 wks h, 8–12 wks in strawberries and other crops. Aphids in brassicas, cereals and hops.

chlorpyrifos Lorsban, OP long Aphids, caterpillars, spider Good except mh, 0.5 wks h, 6–8 wks mh, 2 wks h, ? wks h, ? wks Equity etc mites, blossom weevil, against resistant vine weevil in strawberries. melon-cotton aphid

nicotine XL All 95% alkaloid short Aphids, capsids, Good and should h, 1 wk h, 1 wk ? h, 0 wks ? nicotine leafhoppers, sawflies in control resistant melon soft fruit and other crops and cotton aphid

pirimicarb Aphox carbamate short Aphids in strawberries Good except against s mh, 3 wks s s, larvae s and many other crops resistant melon and h, adults cotton aphid 1 wk

pymetrozine Chess WG* azomethine moderate SOLA (no label recommen- Good sh s s ? s, mummy Plenum WG* dations) for aphid control mh, adults in strawberries. Approved 1/2 wk for control of aphids in many other crops

thiacloprid Calypso chloronicotinyl long SOLA on outdoor & Good mh ? ? ? mh protected strawberry for adults capsid control until Dec 05. ? wks Rosy apple aphid in apple.

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

Hazards Harvest interval Maximum number Buffer zone (days) of sprays width (m)* Anticholin- Humans Fish & other Bees esterase? aquatic life

bifenthrin no h, i ed ed 0 2 per year 18

chlorpyrifos yes h, i ed d 14 3 per year 18

nicotine no t d h 2 u u

pirimicarb yes t, h vt le 3 u u

pymetrozine no u h hr 12 weeks 3 per crop u

thiacloprid no h h u 3 Maximum total dose 30 500ml product per year h harmful hr high risk t toxic i irritant le has little effect * buffer zone distances are for broadcast d dangerous u uncategorised/unclassified/unspecified air-assisted sprayers ed extremely dangerous vt very toxic

Glossary of terms: Latency period: Semi-persistent: Time between aphid ingesting the virus A virus that does not permanently infect Acquisition: and it then becoming established in the the aphid vector, requires long periods Period of feeding needed for the aphid gut system for subsequent of feeding to acquire, and many hours aphid to ingest or 'acquire' the virus infection to a host plant to successfully transmit. Note that strawberry plants once infected with Circulative: Persistent: viruses are permanently infected. Virus remains and reproduces within Remaining within the aphid gut system the aphid gut system Transmission: Replicative: To pass on the virus to the plant Inoculation access period: Virus particles replicate (ie increase in Period of feeding for the aphid to number) within the aphid vector's body pass the virus in to the plant and are not just carried on the mouthparts

Whilst publications issued under the auspices © 2005 Horticultural Development Council. of the HDC are prepared from the best available No part of this publication may be reproduced in information, neither the authors or the HDC can any form or by any means without prior permis- accept any responsibility for inaccuracy or sion of the Horticultural Development Council. liability for loss, damage or injury from the appli- December 2005 cation of any concept or procedure discussed. Design and production: HDR Visual Communication