Introduction

Leafhoppers are widespread, serious pests of many herb species, whether grown under protection or in open field. The damage they cause can be highly detrimental to the appearance of the crop and lead to substantial losses in marketable yield. As a result, growers experience not only direct yield reduction but also increased harvesting and processing costs. Below we outline the Integrated Pest Management techniques to be considered for the control of this challenging pest.

Recognition and host plants

Sage leafhopper

The most common leafhopper species found on protected herbs is Eupteryx melissae, the chrysanthemum leafhopper, often known by growers as the ‘sage leafhopper’. Sages, both those grown as edible herbs and those grown as ornamentals, are often severely damaged. Other commonly-damaged herbs include balm, basil, bergamot, French lavender, mint, marjoram, oregano, rosemary and thyme. Various weed species can also act as hosts, e.g. burdock, dead-nettle, fleabane and horehound.

Adult E. melissae are approximately 3 mm long, pale green with distinctive brown and black spots on the body and wings (Fig. 1). They are very active and flit from the plants when disturbed. The eggs are laid in the leaf veins and petioles and are not easily detected, even under a microscope. The young nymphs that hatch from the eggs are pale yellowish-green (Fig.2), and the older nymphs develop dark bands across the body and the tips of the developing wing buds. The nymphs are much less mobile than the adults and are usually found under the leaves next to a leaf vein. There are five nymphal stages. When each stage moults, the cast skins left behind on the leaf can be mistaken for live leafhoppers. The final nymphal stage develops into the adult.

Glasshouse leafhopper

The glasshouse leafhopper, Hauptidia maroccana can damage a range of protected crops e.g. cucumber, tomato and ornamentals such as Fuschia, Pelargonium and Primula, and will also damage many of the herbs listed as host plants of the ‘sage’ leafhopper. Common weed hosts include chickweed. Adults are a similar size to those of the ‘sage’ leafhopper but are whitish-yellow, with two dark grey chevron-shaped marks on the wings (Fig. 3). The nymphs are whitish without any distinctive markings.

Potato leafhopper

The potato leafhopper, Eupteryx aurata can be a minor pest of potato, but can also damage various outdoor and protected labiate herbs, particularly mints. Weed hosts include nettle and hogweed. The adult is larger (3.5-4mm long) than the ‘sage leafhopper’ and has a pale yellow or orange body, with distinct black net-like markings. The nymphs are whitish.

Green leafhopper

The ‘green’ leafhopper, Empoasca decipiens, is a polyphagous species, which can damage various protected crops e.g. cucumber and sweet pepper. Thyme is a common herb host. Adults are plain bright green and the nymphs are pale green.

Symptoms

Leafhopper damage has the appearance of indistinct white or pale yellow spots or flecks on the leaves, which later coalesce to form bleached areas (Figs 4 and 5). Small black faecal spots left by the leafhoppers on the leaves are sometimes visible (Fig. 4).

Sources of infestation and favourable conditions

The ‘sage’ leafhopper overwinters as eggs in host plant stems and also as adults or nymphs, both outdoors and under protection. Thus it is more of a problem on perennial crops, e.g. sage, and on protected herb nurseries where infested stock plants are kept from one season to the next. The pest is more active between spring and autumn, when adults can migrate into glasshouses from outdoor hosts including weeds, and population increase is favoured by warm temperatures. Short-term pot herbs grown from seed are less susceptible, particularly if preferred host plants such as sages are not grown on the nursery.

Cultural control of Leafhoppers in herbs

Cultural control is a foundation principle of integrated pest management. In this section we consider the contributions of the environmental to leafhoppers 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 Leafhopper in Field Herb Production 

The source of the pest can be either infested stock plants or old crop, weeds or a natural influx spread by climatic conditions. The first two are the most common sources of infestation and as a result, field hygiene procedures are key to avoiding and reducing populations:

• Growers should check their own plant propagation facilities and keep these plants in a separate structure from any used for protected protection. Bought in plants or cutting material should be carefully checked for infestation. Any plants found to be infested should be disposed of carefully.
• Weeds around the production area should be controlled to prevent colonies becoming established to infest crops. Crops should be planned so that particularly vulnerable species e.g., rosemary, be grown away from field margins or hedges. Quick growing crops such as coriander or parsley may be established around other herb crops – the regular sowing, harvest and stubble destruction may help to give a barrier around crops prone to attack.
• Suction machines have been tested for removing leafhoppers from field crops – see AHDB project FV 330. Although they can initially appear to be locally successful, leafhoppers fly off the plant when disturbed, and the nymphs live on the underside of the leaves. In practice they quickly return to the crop.
• Large rolls of adhesive trap materials could be erected around herb crops. In theory the leaf hopper’s characteristic flight would mean that they are unlikely to pass over the traps, but wind and convection can limit effectiveness.
• It is purely anecdotal, but some growers have noted that timed intermittent sprinkler irrigation can assist in keeping leafhoppers moving and may help to prevent them from feeding. There are of course issues then with leaf surface moisture which may encourage foliar diseases, and other operations such as harvest may be hindered.
• 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.

 

Cultural Control of Leafhopper in Protected Herb Production 

Leafhoppers are attracted to both yellow and red sticky traps although the preference for colour does vary by species. The use of sticky traps and weekly counts of population is highly advised to identify the first entrance of the pest to the crop and any peaks in population.

Sticky traps are an indiscriminate method of monitoring so give thought to positioning to make sure that their impact on introduced beneficial insects are minimised. Consider positioning in doorways or under vents, to catch adult leafhoppers flying from infested plants to ‘clean’ plants.

In a pilot experiment in project AHDB SP 58, yellow sticky traps were more effective in trapping adult ‘sage’ leafhoppers than red or blue traps when leafhopper numbers were high, but the three colours of traps were equally effective when at lower leafhopper densities https://ahdb.org.uk/news/sage-advice-for-controlling-leafhopper-on-herbs.

The source of the pest can be either infested stock plants or old crop, weeds around the production site or a natural influx spread by climatic conditions. The first two of these being by far the most common sources of infestation; as a result nursery hygiene procedures are key to avoiding and reducing populations:

• Where possible use barrier materials such as insect netting in entrance ways and vents to protect enclosed structures. This can be highly effective when combined with good quarantine on incoming stock plants however it does impact the air movement and ventilation of the structure.
• Maintain strict weed control in and around glasshouses and polythene tunnels.
• Dispose of infested plants carefully and in a way that prevents reintroduction of the pest.
• Prompt management of old or unharvested crop is critical and this should be destroyed or disposed of promptly to prevent infestations occurring which could transfer to younger crops.
• Keep stock plants in a separate structure from those used for propagation or production.
• Quarantine incoming material in a separate production area.
• Avoid taking cuttings from infested stock plants.
• On Field herbs, a suction machine was tested in 2008 for removing leafhopper from field crops. Results of this AHDB-funded project are available in the report for project FV 330. Although they can initially appear to be locally successful, leafhoppers fly off the plant when disturbed, and the nymphs live on the underside of the leaves. In practice they quickly return to the crop.

 

Biological Control of Leafhoppers in Herbs

There is no biological control agent currently marketed specifically for the control of leafhopper on herbs. However, several biological control agents can have activity on leafhopper species more generally, leafhoppers do remain one of the more difficult pests to manage purely with cultural and introduced biological control. It is suggested that biological control is introduced early in any infestation if good control is to be achieved.

Biological control of leafhopper in Field Herb Production 

Biological controls against leafhoppers are unlikely to be totally effective on an Field 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 leafhoppers under the material.

ADAS tested Steinernema feltiae on protected herbs against sciarid flies and research showed that they can kill leaf hopper nymphs under ideal conditions for the nematodes (Bennison & Green 2007). “Entonem” is approved for all edible and non-edible crops, but the typically variable conditions on open field herb crops mean that growers are best to exercise caution if considering nematodes as the primary method of control in field production.

Lacewing larvae Chrysoperla carnea are used by some herb growers on protected crops as part of their control strategy against aphids. Growers may wish to consider adding them inside low tunnels, subject to the issues discussed above. The larvae will also feed on other pests such as whiteflies, spider mites, thrips and moth eggs. Laboratory studies by ADAS have shown that C. carnea larvae will feed on “sage” leaf hopper eggs on sage, but further work will be needed to test their commercial potential against this pest.

 

Biological control of leafhopper in Protected Herb Production 

1. Anagrus atomus

Anagrus atomus is a tiny parasitic wasp, less than 1 mm long (Fig. 6). The adult females lay their eggs inside leafhopper eggs in the leaf veins or petioles. Parasitised glasshouse leafhopper eggs turn red (Fig. 7). ‘Sage’ leafhopper eggs are laid deeper in the leaf veins than glasshouse leafhopper eggs, so are more difficult to see. Each immature Anagrus develops inside a parasitised ‘sage’ leafhopper egg and its dark body can only just be seen through the leaf vein or petiole tissue (Fig. 8).

Anagrus is commercially available and also occurs naturally on herb nurseries where IPM is used (Bennison, 2001). Initial research on Anagrus was aimed at the control of the glasshouse leafhopper on tomatoes, and this led to successful control of the pest within IPM on commercial tomato nurseries. Research in this project showed that releases of Anagrus onto mint and sage plants reduced numbers of ‘sage’ leafhoppers per plant (Bennison & Green, 2007). Further research and development work would be needed to determine effective release rates and timings.

2. Steinernema feltiae

Insect-pathogenic nematodes, including Steinernema feltiae, were first developed as compost drenches for control of ground-dwelling pests, and they are commonly used on protected herbs against sciarid flies. Growers of other horticultural crops, e.g. chrysanthemums, are now using S. feltiae (‘Nemasys’) as foliar sprays against thrips. Defra-funded research by ADAS tested foliar applications of ‘Nemasys’ against ‘sage’ leafhopper nymphs on sage. The results of the pilot experiment demonstrated that S. feltiae can kill ‘sage’ leafhopper nymphs under ideal conditions for the nematodes (Bennison & Green, 2007). http://sciencesearch.defra.gov.uk/Document.aspx?Document=HH3118TPC_5189_FRP.doc. 

The nematodes enter the leafhopper nymph through the mouth or anus and release symbiotic bacteria, which kill the leafhopper. Infected leafhopper nymphs often have a dark brown head or rear end of the body (Fig. 9).

Further research would be needed to determine methods for effective application of nematodes to herbs for the control of leafhoppers.

3. Anthocorid bugs

Anthocorid bugs are generalist predators, feeding on a range of small invertebrates, and sometimes occur naturally on protected crops where IPM is used. Leafhoppers have been reported as a suitable prey for rearing Anthocoris nemorum.  This species is not commercially available, but large numbers of naturally-occurring A. nemorum were found on spearmint, together with infestations of the potato leafhopper, in a glasshouse on a commercial herb nursery visited in AHDB project PC 178 (Bennison, 2001). https://ahdb.org.uk/protected-herbs-control-of-glasshouse-whitefly-and-leafhoppers-within-ipm-programmes  Research by ADAS tested whether a related species, A. nemoralis would predate ‘sage’ leafhopper nymphs on sage leaves, as this species used to be available for control of psyllids on pear. No predation occurred over a 24-hour period (Bennison & Green, 2007).

Other Anthocorid bugs include Orius species such as O. laevigatus that are commercially available and primarily used for thrips control (see B6- thrips).  Some species of Orius have also been recorded as predators of leafhoppers, e.g. laboratory tests showed that Orius insidiosus (not native or available in the UK) fed on eggs, adults and larvae of the potato leafhopper, Empoasca fabae. Research would be needed to determine whether Orius species available in the UK have potential for control of leafhoppers.

4. Chrysoperla carnea

Larvae of the lacewing Chrysoperla carnea are commercially available and are used by some herb growers as part of their biological control strategy against aphids. C. carnea will also feed on other pests e.g. whiteflies, spider mites, thrips and moth eggs. Initial laboratory studies by ADAS have shown that C. carnea larvae will feed on ‘sage’ leafhopper eggs on sage. Further research would be needed to test their commercial potential against this pest.

 

Plant Protection Products in the Control of Leafhoppers in Herbs

If the economic threshold for leafhopper 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 Leafhopper 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

In the case of leafhoppers, physical mode of action materials can be difficult to use effectively as the adults fly off the plants when disturbed and the nymphs are live on the undersides of the leaves. Application technique for contact based materials should be considered with care.

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.

Sage Leafhopper was screened against 3 botanical biopesticides and 2 coded conventional insecticides in the 2020 SCEPTREplus project. The control used was Gazelle SG (acetamiprid). The greatest reduction in pest numbers and damage was seen in the control (Gazelle SG) treatment. The full report can be found on the AHDB website, the link can be found within the link 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 at www.pesticides.gov.uk prior to any application being made.

 

Plant Protection Products for Leafhopper control in Herb production

There is a range of products for the control of leafhoppers in herb production (Table 1).  The precise conditions of the approval should be checked prior to any application

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
Pyrethroid Deltamethrin Lambda-cyhalothrin  Pyrethrins	Decis Protech Hallmark with Zeon Technology Spruzit

Low Risk in IPM

The following products are safe to biological control agents once spray deposits are dry, and may give some control of leafhoppers. All act by contact only, so good coverage of the undersides of the leaves is necessary:

• Eradicoat or Majestik (maltodextrin),act by physical means. Approved for use on all protected edible and non-edible crops
• FliPPER (potassium salts) has approval but like the above it relies on contact for its effect so good coverage and good application practice is essential

 

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 Field 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. No effect on leafhoppers is claimed on the product label although there may be some useful effect.
• Spirotetramat is a two-way systemic insecticide. It is normally used for aphid or whitefly control but all sucking insects are theoretically affected. Ingesting the active ingredient orally, with subsequent growth and development disrupted and their reproduction is also reduced with fewer viable offspring. Growers should note that spirotetramat has no knock down activity and works best when plants are actively growing. Movento has an EAMU approval for use on protected and outdoor herbs.
• Gazelle SG – Acetamiprid, does have approval for use in herbs via EAMU and has a strong knockdown on the pest as found in recent Sceptre trials. However as a neonicotinoid, Acetamiprid also has a significant impact on the elements of biological control on a nursery and reintroduction of biologicals after an application will need to be considered and factored into decision making. It has relatively short persistence of effect though so can be used successfully with care.

 

Harmful in IPM

Synthetic pyrethroids such as Eribea (alpha-cypermethrin), Decis Protech (deltamethrin), Clayton Lanark, Hallmark with Zeon Technology, Markate 50 (all lambda-cyhalothrin), may give some control, but are purely contact in action, so complete coverage of the leaves is necessary to have a good effect.

Pyrethroids may be harmful to all other insect life, including beneficial species for up to three months after application.

 

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.

 

Further information

Bennison, J. (2001). Protected herbs: control of glasshouse whitefly and leafhoppers within IPM programmes. Final report for HDC project PC 178.

Bennison, J. & Green, K. (2007). Protected herbs: Best Practice Guidelines for integrated pest and disease management. Final report for Defra project HH3118TPC and HDC project PC 210. (available from the HDC).

Cole, R. (2003). Herbs: an independent field and crop evaluation of pesticides to fill identified gaps. Final report for HDC project FV PC HNS 245.

Lole, M. (2009). Field-grown herbs: Evaluation of a mechanical method for the cultural control of leafhoppers. Final report for HDC project FV 330.

https://ahdb.org.uk/fv-330-field-grown-herbs-evaluation-of-a-mechanical-method-for-the-cultural-control-of-leafhoppers

https://www.biobestgroup.com/en/side-effect-manual

https://sideeffects.koppert.com/?L=28

SP 58 Reviewing and testing control measures for leafhopper in Field and protected herbs.

Pesticides.gov.uk

https://ahdb.org.uk/protected-herbs-control-of-glasshouse-whitefly-and-leafhoppers-within-ipm-programmes

http://sciencesearch.defra.gov.uk/Document.aspx?Document=HH3118TPC_5189_FRP.doc

Sceptreplus leafhopper final report

https://ahdb.org.uk/news/sage-advice-for-controlling-leafhopper-on-herbs

https://ahdb.org.uk/amber

https://warwick.ac.uk/fac/sci/lifesci/wcc/research/biopesticides/amberproject