Aphids - HDC Herb Best Practice Guide

Integrated Pest Management of Aphid in Herb Production

A best practice guide for integrated management of Aphid species in protected and field herb production.

Introduction

Several species of aphids can infest herbs grown under protection and/or outdoors. The presence of aphids or their cast skins on the plants, the sticky honeydew excreted by aphids and the associated sooty moulds, and the direct damage caused by aphid feeding can all make potted and cut fresh herbs unmarketable.

Cultural Control of Aphid in Herbs

Cultural control is a key stone of integrated pest management. Monitoring of pest levels and consideration of the hygiene of plant material, environmental conditions and other physical factors is a founding principle of any IPM plan

Biological Control of Aphid in Herbs

Biological control agents are used to build on cultural measures and provide a background level of control, allowing growers to manage pest levels to an acceptable level. In this section we outline the biological options for Aphid control and their use profile.

Plant Protection Products in the Control of Aphids in Herbs

When biological control and cultural management is no longer sufficient to manage an Aphid population at an economically reasonable level, growers will need to look to plant protection product options. In this section we outline the products currently available and the considerations growers and agronomists should evaluate when deciding between them.

Cultural Control of Aphid Species in Herbs

Cultural control is a foundation principle of integrated pest management. In this section we consider the contributions of the environmental to Aphid success or failure and those factors that can be used or manipulated to reduce the pests ability to thrive. It’s also through cultural control that growers can avoid or reduce the frequency of introduction of pests to their growing system and potentially disrupt their life cycle. Monitoring of pest levels and identification of critical thresholds also falls into this section.

Cultural Control of Aphids in Field Production

Aphids produce winged forms for migration, e.g. to move from winter to summer plant hosts, or to find fresh plant material when either colonies get overcrowded or when the host plant is senescing. Otherwise, aphids produce wingless offspring, which usually stay on the original plant, but can also walk to adjacent plants. Aphids give birth to live young and large colonies can build up very quickly in warm weather. Cultural controls options for aphids in field herbs are limited. The pest can be concentrated on stock plants, old crop or a natural influx spread by climatic conditions. Although specific herb aphid species are not generally part of the Pest bulletin, the bulletin can be a useful source of information on incoming influxes and give an alert for favourable conditions and additional detailed scouting in field. When planning production areas thought should be given to any specific site issues. Field margins may be hosts for aphids, hawthorn hedging and carrots fields can play host to hawthorn parsley aphid and willow carrot aphid respectively. However, field margins can also provide an opportunity to boost the natural aphid control within the field by planting aphid predator supporting plants such as phacelia, that attract and support beneficial insects such as hoverfly. It is also possible for these functional plant species to be sown at intervals throughout the crops. Efficient crop destruction can help reduce numbers without chemical control. In field situations gas burning is particularly useful before crop residues are destroyed with a mower collector. Crop covers, either laid directly on the crop, or over hoops to protect the material rubbing directly on delicate foliage are the only method with a degree of reliable control. They require a high level of management with careful sealing to the ground to prevent ingress by any insect pest. Issues can arise when a crop is uncovered, partially harvested, and re-covered resulting in insects becoming trapped under the covers with a readily accessible food source. It could be argued that an application of insecticide immediately after covering would prevent this. In all production scenarios growers should check bought in plant material before bringing in to production areas or planting into the field. The infestation you bought in is one of the most frustrating to encounter and control.

Cultural Control of Aphids in Protected Production .

Winged aphids can migrate into glasshouses and tunnels through vents and doors from Field crops or weeds, or can fly from infested plants in the glasshouse or tunnel. For example, the source of an infestation of willow-carrot aphid on protected parsley, on a nursery visited in AHDB project PC 178, was thought to have been an adjacent Field crop of carrots (Bennison, 2001) and local hawthorn hedges can act as a reservoir for hawthorn parsley aphid. Aphids produce winged forms for migration, e.g. to move from winter to summer plant hosts, or to find fresh plant material when either colonies get overcrowded or when the host plant is senescing. Otherwise, aphids produce wingless offspring, which usually stay on the original plant, but can also walk to adjacent plants. Aphids can be found all year round under protection, but are more of a problem in heated structures and between spring and autumn in unheated glasshouses or tunnels. Aphids give birth to live young and large colonies can build up very quickly in warm weather. Targeted monitoring at these points of migration can be useful in identifying early crop infestations. Be aware that sticky traps may not be useful for monitoring aphids as they catch only winged aphids and also have an appreciable impact on populations of non-pest species that may fly into the glasshouse or tunnel. Check leaves and stems for live aphids, cast skins and malformed or sticky leaves. Curly parsley is a particularly attractive host for most of the aphid species affecting herb crops so may be worth particular attention when monitoring. Hawthorn parsley aphid forms particularly thick colonies at the base of the plant stem and needs early scouting to identify. If using aphid parasitoids check percentage parasitised aphids (‘mummies’) every week and monitor the mummies for signs of any hyperparasitism. If this establishes it can devastate the efficacy of programs that ecpect generations of parasitoids to hatch during production (long cycle herbs). If using Aphidoletes, hoverflies or lacewings, check for predator larvae amongst aphid colonies. In protected environments the close control of weed species and disciplined disposal of ‘old’ and infected crop is vital to reduce the chances of an aphid infestation. There is evidence that bordering particularly vulnerable crops such as parsley with herbs of a different family such as chives can disrupt the aphid colonisation of the crop. In practice this can be difficult to achieve as the guard crop can be needed in significant numbers to get sufficient effect. If practical the use of a repellent guard crop can be an effective technique when combined with biological controls. Netting of screens and doorways is a very effective method for prevention of winged aphids entering production areas but this does impact the airflow and practical management of protected production. Often the practicalities outweigh the benefits. If using insect netting, ensure that the gauge of material used is appropriate to the pests you are attempting to control. Hot water or steam treatment of any recirculating equipment within glasshouses (benches/trays/gutters) is extremely helpful in reducing reintroduction and accumulation of issues both for aphid and other critical pests and diseases. In all production scenarios growers should check bought in plant material before bringing in to production areas or planting out. The infestation you purchase is one of the most frustrating to encounter and control.

Useful Information

https://ahdb.org.uk/amber www.pesticides.gov.uk
Sceptre plus efficacy trials AHDB aphid day webinar
Bennison, J. (1992). Cucumbers: aphids, Integrated Control. Final report for AHDB project PC 69.
Bennison, J. (2001). Protected herbs: control of glasshouse whitefly and leafhoppers within IPM programmes. Final report for AHDB project PC 178.
Bennison, J. (2011 & 2012). Protected herbs: improved biological control of aphids. Annual reports for AHDB project PE 006 & PE 006a.
Bennison, J. (2012 & 2013). Maintaining the expertise for developing and communicating practical Integrated Pest Management (IPM) solutions for horticulture (EMT/AHDB/HTA Fellowship). Interim report for AHDB project CP 089.
Jacobson, R. (2010 & 2011). Sweet pepper: Further development of IPM solutions for aphid infestations. Final report for AHDB project 295a & 295b.
Jacobson, R. (2012). An introduction to hyperparasitism. AHDB Factsheet 27/12.

Biological Control of Aphids in Herbs

There are a range of biological control agents that are commercially available for the control of aphids in protected herb production and several which contribute to control in outdoor production. When introducing a macro biological, it should be chosen carefully as some are selective and will not control all aphid species. Times and rates of release within an Integrated Pest Management (IPM) programme should be planned carefully. If necessary, seek advice from the supplier or a consultant

Biological Control of Aphids in Field Herb Production

Biological controls against aphids are unlikely to be totally effective in an outdoor herb crop exposed to “the weather” and there are currently none marketed specifically for this purpose. Growers using low tunnels sealed to the ground could potentially introduce beneficial insects. Careful management at cover removal would be needed – ideally the whole area uncovered would need to be harvested to prevent trapping leaf aphids under the material.

It is often noted by growers of outdoor herb production that Aphidius sp do naturally occur in their crops but rarely achieve the numbers that would be required to offer the degree of control seen in protected crops. Other predator species such as Chrysoperla carnea (lacewing larvae), Episyryphus balteatus (hoverfly) and Adalia bipunctata (2- spotted ladybird) occur naturally and should be encouraged using dedicated beds of insect friendly plants such Phacelia and wild flower mixes.

Biological Control of Aphids in Protected Herb Production

1. Aphidius colemani
Susceptible aphids:
Peach-potato aphid (Myzus persicae)
Melon and cotton aphid (Aphis gossypii)
Hawthorn-parsley aphid (Dysaphis apiifolia) NB. A. colemani does not parasitise mint aphid (Ovatus crataegarius)

Aphidius colemani is a small (about 2 mm long) brown and black parasitic wasp. The adult female lays a single egg into each aphid (Fig. 2). The parasitoid develops inside the aphid body, turning the aphid into a pale brown ‘mummy’ . When fully developed, the adult parasitic wasp cuts a round hole in the top of the mummy and emerges. Where IPM is being used aphid parasitoids can occur naturally, but usually these are not sufficient to provide full control. A. colemani is supplied as parasitised mummies in tubes. The adults emerge from the mummies in the opened tube in the glasshouse or tunnel over the following few days. Aphidius are best released weekly on a preventive basis, as the adults are very mobile and efficient in finding their hosts, and will often find the first aphids before they are detected by crop monitoring. Waiting until the first aphids are seen is often too late for starting parasitoid releases. Once aphids are seen, parasitoid release rates should be increased. Aphid ‘mummies’ can sometimes be parasitised by hyperparasitoids which can threaten biological control of aphids. Hyperparasitoid adults emerging from mummies leave a ragged emergence hole rather than the neat, round hole made by the primary parasitoid . The incidence of hyperparasitoids in various crops has been studied in AHDB projects CP 089 and in sweet peppers in AHDB project PC 295a and 295b (Jacobson, 2010, 2011 & 2012). If hyperparasitised mummies are seen, it is advisable to use aphid predators in addition to parasitoids as the hyperparasitoids can threaten successful biological control.

Fig 1: Aphidius colemani lays a single egg into each aphid

2. Aphidius ervi

Susceptible aphids:
Glasshouse-potato aphid (Aulacorthum solani)
Potato aphid (Macrosiphum euphorbiae) – not usually a pest of herbs.

This black parasitic wasp is very similar to A. colemani, but it is about twice the size (Fig. 11). The parasitised aphid mummies are brown like those of A. colemani (Fig.12)

3. Aphid parasitoid mixtures

If a mixture of herbs is grown that is susceptible to a range of aphid species, it may be necessary to release more than one parasitoid species. Various aphid parasitoid mixtures are now available, which offer control of a range of aphid species. For example, one product includes a mix of three parasitoid species in the same tube , i.e. A. colemani, A. ervi and Aphelinus abdominalis. Aphelinusabdominalis attacks some of the same species as A. ervi but the parasitised mummies are black rather than brown.

Other products offer mixtures of up to six parasitoid species, supplied in cardboard tubes (Fig. 13). The mixtures can include Aphidius matricariae, Ephedrus cerasicola and Praon volucre in addition to the three species mentioned in the paragraph above. Each of the parasitoid species in the mix has a specific aphid host range and prefers specific environmental conditions, so the mix has widened the range of aphid species attacked. The species in this mixture were tested by ADAS against two ‘problem’ aphids on herbs (hawthorn-parsley aphid and mint aphid) in AHDB funded project PE 006 & 006a. Hawthorn-parsley aphid was parasitised by four of the species; A. colemani, A. matricariae, A. abdominalis, P. volucre and E. cerasicola. Mint aphid was parasitised by A. matricariae, P. volucre and E. cerasicola. All the parasitoid species are available as individual species except for P. volucre and E. cerasicola which are only available in the parasitoid mix. Aphidius colemani was shown to be as effective as the parasitoid mix in controlling hawthorn-parsley aphid and A. matricariae was as effective as the mix in controlling mint aphid

4. Aphidoletes aphidimyza

This is a midge whose larvae are voracious predators of most species of aphid. It can be used on herbs, to supplement aphid control by parasitoids if necessary. The predator is supplied as pupae in a carrier in tubes, or in release tubs. The adults emerge from the pupae and the female midges fly to find aphid colonies amongst which they lay eggs. The small orange-red eggs hatch in afew days and the yellow/orange maggot-like larvae (up to 2.5 mm long) kill and feed on most aphid species. The larvae drop from the plants to pupate in the growing medium or on the bench or floor, although pupation is more successful in growing media than on bench or floor coverings. Aphidoletes needs a minimum of 15 hours daylength to complete its life cycle, so releases between May and September will allow establishment in the crop, as will releases in shorter daylengths if supplementary lighting is used.

5. Lacewings, hoverflies and ladybirds

Other commercially-available aphid predators are the lacewing larva Chrysoperla carnea (Fig. 2), the hoverflies Eupodes corollae and Sphaerophoria ruepelli and the 2-spot ladybird, Adalia bipunctata. Like Aphidoletes, these predators will eat most aphid species, so can be useful for controlling those aphids not attacked by parasitoids, or if hyperparasitoids are attacking the parasitoids. Lacewing larvae have proved successful in some herb crops. However, unlike the parasitoids and Aphidoletes, these three predators tend not to breed continuously in the crop. Thus they are best used as ‘biological pesticides’ e.g. as an alternative to a pesticide in aphid ‘hotspots’. Lacewings and ladybirds are supplied as larvae and hoverflies as pupae. The predators can also occur naturally in crops where IPM is used.

Fig 2: Chrysoperla carnea

Useful Links

Plant Protection Products in the Control of Aphids in Herbs

If the economic threshold for Aphid damage is exceeded it can be that biological control is no longer managing the pest population to an effective level. At this point growers need to review the plant protection product options available to them

Considerations when Selecting Protection Products for Aphid control

There are a number of considerations when reviewing your spray options, some important examples are below

Speed of response required
Harvest Interval
Location of Target
Method of application
Impact on biological control species
Insect resistance and rotation of actives
It’s also important to recognise that insecticides should not be applied to crops in flower, where bees are actively foraging, or where there are flowering weeds adjacent to the crop
Rotation of control options – resistance avoidance

The impact of the plant protection product on the biological control within the control program as a whole should be considered. Both Koppert and Biobest provide side effects manuals (see useful links section) which give details on the relative harm of different chemicals. Note, following the application of a plant protection product the site may need to increase biological control to re-establish the pre application population and account for losses incurred during treatment.

Due to existing and potential problems with aphid resistance to pesticides, it is very important to follow Resistance Management Guidelines when using a pesticide. There is a LINK to the IRAG guidelines and resources in the links section.

Insecticides should not be applied to crops in flower, where bees are actively foraging, or where there are weeds adjacent to the crop in flower.

Growers should take care to ensure that insecticide from similar groups are not used concurrently and instead are alternated with products from a different group. Specific guidance can be found via the IRAC website in the useful links section.

Chemical approvals regularly change and the listing of a product below does not constitute a recommendation for use. Check the approval status and suitability of application with your BASIS advisor and by checking approval status at www.pesticides.gov.uk prior to any application being made.

Plant Protection Products for Aphid control in Herb Production

There is a range of products for the control of aphids in herb production and given the speed with which resistance can develop in this challenging pest species, this diversity of approach is greatly needed. Table 1 gives an overview of the products available and their insecticide group. The precise conditions of the approval should be checked prior to any application being planned.

Insecticide group and active ingredients	Example Products
Neonicotinoid Acetamiprid	Gazelle
Biological insecticide Beauveria bassiana	Botanigard WP
Keto-enol Spirotetramat	Movento
Physical insecticide Fatty acids Maltodextrin Unspecified physical control agents	Flipper Majestik SB Plant Invigorator
Pyridinecarboxamide Flonicamid	Mainman (outdoor use only)
Pyrethroid Deltamethrin Lambda-cyhalothrin Pyrethrins	Decis Protech Hallmark with Zeon Technology Spruzit

Table 1: Insecticides with activity against aphids permitted on herb crops (March 2021)

‘Low Risk’ in IPM

Botanigard WP (Beauveria bassiana) is an entomopathogenic fungus which enters into the cuticle of susceptible insects, including aphids, germinate and grow into the inner body of the host where it proliferates producing toxins which eventually kill the pest. It has contact activity only and the process which results in the insect turning to a thin white mould takes several days. Certis has developed a best practice guide for this product which it is highly advisable to consult prior to application. Good coverage is essential to producing the right result and the humidity must be above 70% RH at crop canopy for 5-6 hours post application to allow the fungal agent to successfully colonise the pest species. It has approval for both outdoor and protected production.

Flonicamid is a specific aphicide and works as a feeding inhibitor, having no knock down activity. It is systemic, selective with long-term activity. Aphids cease feeding and die within a few days. It is the only insecticide within its class and can be compared to the now withdrawn pymetrozine. It is only approved in outdoor production.

Flipper (fatty acids C7-C20) and Eradicoat, Majestik, Terminus (maltodextrin) all have approvals for edible crops including protected and outdoor herbs. Once dry upon the leaf surface, they have no further effect on the target insect and are safe to beneficial species.

‘Moderately harmful’ in IPM

The following products are harmful to some biological control agents: Spruzit (pyrethrins plus naturally derived oil) and Pyrethrum 5 EC (pyrethrins) are approved for use on protected and outdoor edible crops including herbs. Pyrethrins are harmful to many biological control agents, but only for a few days after application, thus can usually be used with care within IPM programmes.

Some strains of Aphis gossypii and Myzus persicae are resistant to pyrethroids and pyrethrins.

Acetamiprid is a contact and ingested neonicotinoid insecticide, with broad spectrum systemic activity. Growers should not apply to crops in flower because of the danger to pollinating insects. There are EAMU approvals for the use of this active ingredient on protected and outdoor herbs with specific reference to aphids.

Spirotetramat is a two-way systemic insecticide with a novel mode of action whereby it interferes with lipid biosynthesis. Sucking insects ingest it orally, with subsequent growth and development disrupted. Fecundity is reduced with fewer viable offspring. Growers should note that spirotetramat has no knock down activity and works best when plants are actively growing. It also has useful activity against whitefly. Movento has an EAMU approval for use on protected and outdoor herbs with specific reference to aphids.

‘Harmful’ in IPM

Growers have a number of options from those with specific activity against aphids such as neonicotinoids, or broad spectrum pyrethroids that may be harmful to all other insect life, including beneficial species for up to three months after application.

The pyrethroid insecticides Eribea (alpha-cypermethrin), Decis Protech (deltamethrin – outdoor production only), Clayton Lanark, Hallmark with Zeon Technology, Markate 50 (all lambda-cyhalothrin – all outdoor production only), may give some control, but are purely contact in action, so complete coverage of the leaves is necessary. Some strains of Aphis gossypii and Myzus persicae are resistant to pyrethroids and pyrethrins.

Application Practice

Growers should be mindful of nozzle technology in their pesticide application equipment to achieve adequate leaf surface cover of both the top and bottom sides when applying physical or contact products. The use of angled nozzles is of particular interest to improve coverage. Water volumes are also important to consider as it can be a false assumption to use large volumes even in crops and situations where significant coverage is needed.

Water sensitive paper can be used to ascertain the degree of coverage and careful siting will mimic the pesticide deposition on each surface of the leaf.

More information on this topic can be found within the AMBER project which specifically addressed some of these points.

Where using biological control agents it is important to tailor the application to the requirements of the active agent. In this case for Botanigaurd there is some excellent guidance in the CERTIS best practice guide, see useful links section.