B1 – Leafhopper

Introduction

Leafhoppers are widespread, serious pests of many herb species, whether grown under protection or outdoors. Leafhopper damage is unacceptable to retailers. Leafhopper damage currently leads to substantial crop losses in potted herbs and in those grown for cutting, and may also add labour costs in selecting plants for cutting or picking off damaged leaves prior to sale.

 

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.

 

Integrated Pest management (protected herbs)

Cultural control

As the source of the pest is usually either infested stock plants or weeds, nursery hygiene procedures are key to avoiding or reducing infestations:

• Maintain strict weed control in and around glasshouses and polythene tunnels.
• Dispose of infested plants carefully.
• Keep stock plants in a separate structure from those used for propagation or production.
• Avoid taking cuttings from infested stock plants.
• Yellow sticky traps may be useful in doorways or under vents, to catch adult leafhoppers flying from infested plants to ‘clean’ plants. However, these will also catch flying beneficial insects, e.g. parasitic wasps, so they should be used and positioned with care.
• On outdoor herbs, a suction machine was tested in 2008 for removing leafhopper from field crops. Results of this HDC-funded project are available in the report for project FV 330.

 

Biological control

There is no biological control agent currently marketed specifically for the control of the ‘sage’ leafhopper on herbs. However, several biological control agents have potential against the pest:

1. 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. 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). 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. Large numbers of A. nemorum were found on spearmint, together with infestations of the potato leafhopper, in a glasshouse on a commercial herb nursery visited in HDC project PC 178 (Bennison, 2001). A. nemorum is not available commercially but a related species, A. nemoralis is now available for the control of psyllids on pear. Research by ADAS tested whether A. nemoralis would predate ‘sage’ leafhopper nymphs on sage leaves. No predation occurred over a 24-hour period (Bennison & Green, 2007).

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.

 

Chemical control (protected herbs)

Chemical control of leafhoppers is difficult, as the adults fly off the plants when disturbed, e.g. during spraying, and the nymphs are difficult targets as they live on the undersides of the leaves. A pesticide should only be used if necessary and should be selected carefully, taking into account pesticide compatibility within IPM (see section A – Principles of IPM) and harvest interval (see Table 2 on the homepage). There is no known leafhopper resistance to pesticides in the UK, but it is still important to follow Resistance Management Guidelines when using a pesticide (see Section A – Principles of IPM and Table 2 on the homepage).

For further information on safety of pesticides to individual biological control agents, consult your biological control supplier. General guidelines on the selection and compatibility of pesticides within IPM are given below:

‘Safe’ 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.
• Savona (fatty acids), has an Extension of Authorisation for Minor Use (EAMU) for use on protected leafy herbs.

‘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.
• Calypso or Agrovista Reggae (thiacloprid), are neonicotinoid insecticides with EAMUs for use on protected leafy herbs. Calypso was shown to be effective against ‘sage’ leafhopper on sage in HDC project FV PC HNS 245 (Cole, 2003). Its 14-day harvest interval limits its practicality on short-term herb crops, but it could be useful for end of season clean-up of the pest on stock plants (but N.B. the EAMU restricts use to between 1 April and 31 October).

‘Harmful’ in IPM
The various pyrethroid products cypermethrin and deltamethrin have EAMUs for use on protected leafy herbs. They may give some control of leafhoppers but are purely contact in action, so good coverage of the undersides of the leaves is necessary. Pyrethroid insecticides are harmful to biological control agents for up to three months after application, thus they are incompatible with IPM.

• Full details for the use of biological control agents and compatibility of pesticides are available from biological control suppliers or consultants. Also see Section A – Principles of IPM.
• Pesticide approval information in this guideline is current at 29 April 2013.
• Regular changes occur in the approval status of pesticides arising from changes in pesticide legislation or from other reasons. For the most up to date information, please check with a professional supplier or the CRD website http://www.pesticides.gov.uk/.  General enquiries on pesticides and detergents are now being handled by the Defra Helpline (as of April 2013): Tel: 08459 33 55 77.
• Always follow label recommendations or statutory conditions for use on Extension of Authorisation for Minor Use (EAMU).
• Always follow instructions for Pesticide Resistance Management guidelines given on the label or EAMU.
• Growers must hold a paper or electronic copy of the current EAMU before using any product under the EAMU arrangements. Any use of a pesticide with EAMUs is at grower’s own risk. Relevant EAMUs are sent to HDC members by HDC, or are available from CRD (see above) or from consultants.
• Use pesticides safely.

 

Further information

HDC Factsheet 05/01. Glasshouse whitefly and leafhoppers in protected herbs: options for control within IPM programmes.

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.