IPM combines cultural and biological control methods with the minimal use of pesticides. Any pesticides selected for use in IPM should have minimal impact on introduced or naturally-occurring biological control agents. IPM programmes will vary according to the herb species and crop grown. Each IPM programme needs to be planned carefully, taking into account the pests and diseases likely to occur on each crop, the environmental conditions in the glasshouse or polythene tunnel and the range of cultural methods, biological controls and compatible pesticides available. Growers who are experienced in IPM will be able to build on previous experience of IPM successes, whereas growers new to IPM will need more support and information to help them plan and use IPM effectively. The best-practice guidelines described here are intended as a supplement rather than a substitute for advice and support from IPM consultants and biological control suppliers. New biological control methods are being continually developed, so IPM best practices are constantly evolving, and it is important for growers to keep up to date with new developments as they become available.
Prediction, monitoring and diagnosis
The aim of predicting, monitoring and diagnosing pest and disease problems is to enable the most effective IPM programme to be planned and managed.
Prevention of pest and disease problems is preferable to curing them if possible, and predicting potential problems can play an important preventive role. Prediction of pest and disease risk also enables management strategies to be appropriately targetted. Risk of a particular pest or disease developing depends on many factors including:
- Presence of the pest or disease on a previous or adjacent crop, crop debris, weeds or on plant material (including seed) brought onto the nursery.
- Presence of the pathogen in sufficient quantities to cause disease.
- Presence of a susceptible host crop.
- Favourable environmental conditions and time of year.
- Cultural control methods being used.
Referring to records from crop monitoring, observations and management strategies used on each herb crop thus plays an important role in helping to predict the risk of pests and diseases.
Monitoring and recording of monitoring results are essential components of effective IPM, in order to take effective decisions and prompt action. Monitoring needs to be frequent and regular (ideally, weekly), due to the ability of pests to build up rapidly in favourable conditions, and to the ability of certain diseases such as powdery mildew, leaf spots and grey mould to develop and spread rapidly as a result of abundant spore production and transmission by air currents or water splash. Monitoring needs to be done by an experienced member of staff who has been trained to recognise pests, diseases and their damage symptoms.
Monitoring environmental conditions
Monitoring environmental conditions (e.g. temperature, relative humidity, leaf wetness duration) as well as knowledge of the factors that favour or delay development of particular pests and diseases (see Sections B and C), can help to determine the risk of pest and disease development. Monitoring temperature, day length, relative humidity and compost or soil moisture can also check that environmental conditions are suitable for specific biological control agents (see Section B).
One method of detecting the presence of a pathogen before symptoms develop is by spore trapping. Simple methods, such as trapping of spores of Botrytis cinerea on plates of a selective agar medium, can be used to compare grey mould risk in different areas of a nursery or pack-house. More sophisticated techniques involve use of air-suction spore traps to collect spores for microscopic examination or for detection by immunological or molecular methods.
Where symptoms of pests or disease have developed, early detection and prompt action can prevent further damage occurring and prevent further spread. Remember that symptoms may not be immediately obvious. For diseases that are favoured by high relative humidity (e.g. grey mould), check for symptoms at plant bases and in parts of the crop where foliage is most dense or in contact with the growing media. Symptoms of downy mildew may only be evident if leaves are checked on the underside, while powdery mildew can be particularly difficult to spot when foliage is wet. When monitoring for pests, it is important to know where to look, e.g. some aphid species are likely to be on leaf undersides whereas others will be on stem bases (see Section B.4). In addition to checking the plants visually, tapping plants onto a white plastic tray or clipboard can be a useful method for monitoring pests such as thrips that can hide in growing points. Use of a x10 or x20 hand lens is necessary to see very small pests such as spider mites, and to recognise different species of other pests such as aphids (see Sections B.1-12 for recognition guidelines for all key pests). In addition to monitoring plants for pests and pest damage, it is necessary to check for biological control agents and make appropriate records, e.g. percentage parasitised aphids. Monitoring methods for specific pests and biological control agents are given in Section B.
Trap or indicator plants
Many pests prefer certain herb species or varieties and these can be used as indicator plants, for special attention during monitoring. Example indicator plants include parsley for sciarid fly, mint and basil for shore fly and leaf miner, sage for leafhopper, and chives for thrips. Trap plants that are known to be more attractive than the crop to certain pests have been used in other horticultural crops as ‘lure’ plants, e.g. tobacco or aubergine plants have been used in poinsettia for whitefly. Infested trap plants can either be regularly disposed of to prevent them acting as breeding sites for pests, or they can also be used as ‘banker plants’ for biological control agents such as Encarsia formosa for whitefly control (see Section B.5).
Sticky traps are useful for monitoring flying pests such as thrips, whiteflies, leaf miners and sciarid flies. They should be used in addition to crop monitoring as they only give an indication of the presence or relative numbers of pests in a certain locality, and will not trap non-flying pests such as spider mites. They should not be used for monitoring aphids, as many species of winged aphids can get caught on traps, even ‘incidental’ species that are not pests of herbs, but fly into the glasshouse or polythene tunnel by chance. Certain pests are more attracted to different coloured sticky traps, e.g. whiteflies, leaf miners and sciarid flies are more attracted to yellow, whereas western flower thrips are more attracted to blue.
There are no precise recommendations for the number of sticky traps to use in a given area. As a general guideline, one trap per 100 m2 should be sufficient, and should not make trap monitoring too onerous. Only use as many traps as can be practically monitored, as too many traps can adversely affect biological control by catching large numbers of flying beneficials e.g. parasitic wasps. It can sometimes be useful to position traps over favourite host plants, imported plants and near doorways and heating pipes. Traps should be positioned just above the plants and moved up as the plants grow. Placing the traps about 30 cm above the plants will reduce the numbers of flying beneficials caught. Pests can be removed from traps after weekly checking, or a ring can be drawn round them to avoid re-counting the following week. Traps should be changed regularly as they collect compost debris and plant material in addition to insects, which makes counting and recognition difficult.
Pheromone and lure traps
A pheromone is a chemical signal released by an animal that influences the behaviour of other animals of the same species, e.g. sex pheromones are released by some female insect species to attract males. Pheromone traps are available for some moth species (see Section B.7). They use a sex pheromone lure to attract male moths that are then caught on a sticky card. The traps are useful for early warning of first moth activity, to help time caterpillar control measures. Pheromone lures for use with sticky traps are also available for thrips. The aggregation pheromone attracts both male and female thrips.
Other available lure traps use plant extracts rather than pheromones as lures, e.g. for various thrips species, vine weevil and slugs.
In addition to crop monitoring, stored water used for irrigation, especially re-cycled water, should be regularly monitored for the presence of plant pathogens. Further details of possible techniques can be found in HDC Factsheet 10/07. The lateral flow kits (LFDs) described below can be used for water testing for specific pathogens. Guidelines are currently being developed to enable more effective ‘do-it-yourself’ diagnosis using simple baiting techniques together with LFDs. In addition, the following laboratories currently offer a water testing service for plant pathogens:
Stockbridge Technology Centre
North Yorkshire YO8 3TZ
Dr Tim Pettitt
C/o Eden Project
Cornwall PL24 2SG
Identification of particular pests and pathogens causing damage on protected herbs and knowledge of their biology allows integrated management practices to be tailored to these specific organisms. For common pests and diseases of protected herbs, on-site diagnosis may be possible. To aid diagnosis, Table 1 summarises common damage symptoms that may occur on protected herbs, along with possible causes, and reference to the relevant best-practice guidelines. The descriptions and images provided in the best-practice guidelines are designed to further facilitate diagnosis. Note that plants can suffer from a range of abiotic factors as well as from pest and disease damage. Common problems include incorrect watering (e.g. drought or water-logging), physical damage, and nutritional deficiencies or toxicities. Train staff to recognise common pest and disease problems and to report suspected pest or disease outbreaks promptly.
Accurate pest and disease diagnosis is essential since it provides the starting point for effective management, for example, to aid decisions on product choice for biological or chemical control. Certain pests and diseases that are easily confused can require very different approaches to control. Examples of pest and disease ‘lookalikes’ are given below:
When monitoring sticky traps for pests, sciarid flies (section B3), shore flies (section B2) and other small black flies are commonly confused. It is important to be able to recognise sciarid and shore flies amongst other types of small black flies commonly found on traps, in order to manage the IPM programme. For example, the insect-pathogenic nematodes and predatory mites used against sciarid flies do not control shore flies adequately, and control measures are not necessary for ‘incidental’ flies that are not plant pests, e.g. midges. Figure 1 shows a sciarid fly, a shore fly and a midge. Sciarid flies can be recognised by their long legs, long, beaded antennae and a Y-shaped vein on each wing Shore flies have a robust body, short stubby antennae, and each wing has five pale spots, giving a ‘domino’ effect. Midge adults can be recognised by their characteristic antennae, which have many long hairs.
Recognition of flies on sticky traps. Sciarid fly (left), shore fly (centre), midge (right).
When monitoring plants for pest damage, leafhopper damage (section B1) can often be confused with thrips damage (Section B6), as both pests not only cause white marks on the leaves, but also sometimes damage the same herb crops, such as basil and mint. Figure 2 shows leaf damage caused by leafhoppers and thrips. Leafhopper feeding causes white or pale yellow spots with indistinct edges to appear on the leaves, which coalesce as feeding progresses, to form bleached areas. Thrips feeding produces small white or silvery flecks on the leaves that are more irregular than the circular spots made by leafhoppers.
Two groups of diseases that are commonly confused are the powdery mildews and downy mildews (Sections C.3 and C.4). Some crops, such as parsley, can be affected by both diseases. It is important to distinguish between the two diseases since management practices are different in terms of cultural practices (e.g. modification of environmental conditions) and appropriate fungicide treatment. Diagnosis can be problematic because both powdery and downy mildew can result in white fungal growth on leaf surfaces. A key difference between the two diseases is that powdery mildew tends to be more abundant on upper leaf surfaces, while downy mildew spore production occurs most often on the lower leaf surface (Figure 3). The prevailing environmental conditions can also provide a clue as to which disease is most likely to have occurred, with powdery mildew favoured by warm dry conditions, while downy mildew is more abundant under cool, wet conditions.
Powdery mildew occurs typically on upper leaf surfaces (left) and downy mildew is more usually seen on lower leaf surfaces (right).
Plant wilting may result from root damage by fungi such as Rhizoctonia solani that cause ‘wire-stem’ symptoms (left) or wilt pathogens such as Fusarium oxysporum that invade the vascular system and cause staining.
A symptom that can have a wide range of causes is plant wilting (see Table 1). Even when pests, mechanical damage and drought have been eliminated as possible causal factors, there are several pathogens that can result in plant wilting, each requiring a different management approach. Root rots are a common cause of wilting and may be due to Pythium species, Phytophthora species or Rhizoctonia solani. Pythium and Phytophthora species belong to the same fungal group, while R. solani is from a different group. Cultural practices are similar for all three pathogens but fungicides effective against Pythium and Phytophthora root rots will not control Rhizoctonia root rot. The best-practice guideline on root rots (Section C.1) describes features of root rots caused by different pathogens, however these can still be difficult to diagnose. One common feature of Rhizoctonia root rot that may help distinguish it from other root rots is the development of a ‘wire-stem’ symptom, in which the stem base becomes discoloured and constricted (Figure 4). Wilting can also result from infection by vascular wilt pathogens that enter via plant roots and colonise the vascular system, resulting in reduced water uptake (Section C.6). A common feature of wilt diseases caused by Fusarium oxysporum and Verticillium dahliae, is that dark vascular staining may be seen if the stem is cut longitudinally (Figure 4), while roots may remain visibly healthy.
Diagnostic kits are now available that can provide rapid on-site pathogen detection and disease diagnosis. Kits are currently available for common pathogens such as Botrytis, Phytophthora, Pythium and Rhizoctonia species. The kits usually take the form of a lateral flow device (LFD) that uses similar technology to that of home pregnancy testing kits. Sampling involves a simple technique for sap extraction from plant material, followed by addition of a few drops of the sample onto the device. The test gives a visual result usually in less than five minutes and can provide a useful starting point for diagnosis, although further testing may be necessary if identification to species level is required. Further information can be obtained from Forsite Diagnostics Ltd (www.forsitediagnostics.com ; www.pocketdiagnostic.com).
For situations where a pest or disease cannot be identified, seek advice from a specialist crop consultant or send a sample to a plant clinic for identification. There are plant clinics offering pest and disease identification services at Fera and STC:
The Plant Clinic
Food and Environment Research Agency
York YO41 1LZ
Tel. (01904) 462000
The Plant Clinic
Stockbridge Technology Centre
North Yorkshire YO8 3TZ
Tel. (01757) 268275
Suspect quarantine pests or diseases
If a pest or disease is known or suspected to be a non-indigenous quarantine organism, you must immediately inform your local Plant Health and Seeds Inspector. Contact details are available on the Fera website at www.fera.defra.gov.uk/plants
Examples of quarantine organisms that might occur on UK protected herbs include the tobacco whitefly, Bemisia tabaci, the South American leaf miner, Liriomyza huidobrensis and the Iris yellow spot virus, for which chive is a known host. For details on recognition of these pests and diseases see the following sections:
Tobacco whitefly, Bemisia tabaci B.5
South American leaf miner, Liriomyza huidobrensis B.8
American serpentine leaf miner, Liriomyza trifolii B.8
Iris yellow spot virus C.10
Host plant resistance
In general, disease can be avoided through use of a crop variety that is resistant to a particular pathogen, thus reducing the need for other management practices including chemical control. For diseases of protected herbs, however, there are few examples of resistant varieties that are commercially available. Exceptions are the basil varieties Nufar F1 and Aroma 2 that are reported to be resistant to Fusarium wilt. Nevertheless, varietal differences in disease resistance exist for herb crops. An example of this is mint, for which different species and varieties vary widely in their susceptibility to powdery mildew and also rust. Through crop observation and records, it may be possible to choose varieties that are less susceptible to disease, or to limit production of highly susceptible varieties to parts of the season when environmental conditions are low risk for disease development.
There are no cultivars or varieties of herb species with known resistance to pests, although some are more susceptible than others to certain pests. For example, sage is a favourite host for the ‘sage’ leafhopper and parsley is favoured by sciarid flies, with curly parsley seeming more susceptible than flat-leaved parsley. As with diseases, grower experience on each nursery and records of pest monitoring may allow the selection of less susceptible varieties if this is commercially practical.
Health status of seed and planting material
For certain diseases of protected herbs (e.g. Fusarium wilt of basil, Septoria leaf spot on parsley and bacterial blight of coriander), seed is a primary source of infection. For basil, parsley and coriander in particular, it is important to ensure that seed is obtained from a reputable supplier and that it has been tested and shown to be free from seed-borne pathogens.
Both pests and diseases may be transmitted via vegetative propagation. Examples of diseases include transmission of symptomless grey mould (Botrytis cinerea) and viruses in cuttings, and mint rust on stolons. Examples of pests include leafhoppers or whiteflies on both sage and mint cuttings, plus leaf miners, spider mites or thrips on mint cuttings. Avoid propagation from diseased or pest-infested mother plants, and keep stock plants in separate structures from those used for propagation or production.
All batches of incoming plants should be carefully inspected for diseases, pests and damage symptoms, checking both the leaves and roots. Some pests and diseases may be symptomless at delivery so where space is available, maintain incoming plants in an isolated area for 2-4 weeks and examine them twice weekly. Use of sticky traps above the plants for monitoring any flying pests is recommended. Preventive releases of some biological control agents may be advisable, e.g. predatory mites for thrips control. If a pest or disease is found, action will depend on the pest or disease and the severity of the problem, e.g. plant disposal or treatment with a suitable pesticide or biological control agent.
The HDC Factsheet 10/07 ‘Guidelines on nursery hygiene for outdoor and protected ornamental crops’, provides extensive information that is of relevance to protected herb production. HDC Factsheet 15/05 ‘Use of chemical disinfectants in protected ornamental production’, also provides more specific information on the use of disinfectants in nursery hygiene. The action points from Factsheet 10/07 are reproduced here:
Glasshouse structure, machinery and equipment:
- Clean and disinfect regularly.
- Avoid taking machinery and equipment from ‘dirty’ areas to ‘clean’ areas.
- Store under cover, or shrink-wrap; if stored outside, regularly check on the condition of the wrapping.
- Where containers are re-used, clean and disinfect them first.
- Store old containers separately from new ones.
- Store loose media in a covered bunker on a concrete slab above soil level. If storing media outside, keep it in sealed bales or bags and regularly check on the condition of the wrapping.
- Keep the media mixing area clean.
- Inspect incoming young plants carefully for pests, diseases and weeds.
- Monitor growing crops and stock plants regularly (e.g. weekly) for pests and diseases.
- Remove affected plants promptly.
- As well as checking plants, use sticky traps to monitor for pests.
Benching, standing and growing areas:
- Clean and disinfect regularly between successive crops.
- Renew old capillary matting or woven plastic ground covers, especially those known or suspected to be contaminated with a serious pathogen or pest.
- Ensure ground covers are flush to paths and the base of stanchions to prevent weed growth.
- Level beds to eliminate puddles.
- Control algal growth by avoiding over-watering, ensuring good drainage and, if necessary, use of an algaecide.
- Ensure uniform irrigation.
- Maintain good weed control around reservoirs to prevent seed blowing into the water.
- Cover water-storage tanks.
- Clean irrigation pipework (e.g. every autumn) to prevent algal build-up in pipes and around nozzles.
- Clean roofs and gutters regularly if roof water is collected.
- On propagation nurseries, and where crops susceptible to the common waterborne root-infecting pathogens are grown, decontaminate recycled water or use collected rainwater.
- Test recycled water regularly for fungal pathogens, especially in storage tanks and at the point of use.
- Maintain control of weeds on paths, bed edges, around glasshouses, tunnels, buildings and reservoirs, and at the perimeters of the site.
- Aim for a 1 metre wide weed-free strip around the edges of glasshouses and tunnels.
Waste and crop debris:
- Place in covered containers and empty these frequently.
Manipulation of environmental conditions can provide an important component of cultural practices for control of diseases and of some pests. For many key diseases of protected herbs (e.g. grey mould, downy mildews, rusts and leaf spots), infection and disease development is dependent on conditions of high relative humidity and prolonged leaf wetness duration. Specific information is provided in individual best-practice guidelines (Section C), however general steps to reduce risk are as follows:
- Avoid overhead watering or use only when there is time for foliage to dry before nightfall.
- Where space is available, separate plants in order to improve air circulation.
- Maintain good ventilation, for example by use of venting and/or fans.
- Consider the use of heat boosts (drying periods) during periods of high risk.
- Avoid rapid rises in air temperature that increase the risk of condensation on leaves that are still cold.
Examples of pests that are affected by compost or soil moisture and relative humidity are sciarid flies, shore flies and spider mites. Both sciarid and shore flies are more of a problem in warm, wet conditions, thus avoiding over-watering and maintaining adequate ventilation can reduce their development. Spider mites are favoured by hot, dry conditions, thus use of shade screens, misting the plants with water in hot weather if practical, and maintaining adequate ventilation can reduce spider mite population growth.
Crops that are poorly managed in terms of their growing environment will be more at risk from attack by diseases and pests. Crop management is of particular importance for many herb species that are poorly adapted to UK growing conditions. Crop stress can arise for example when the season is extended into cooler spring and autumn periods. Growing the crop ‘well’ involves implementation or consideration of appropriate soil/media fertility, crop nutrition, watering regime, temperature and lighting, harvesting and packing techniques. Examples where cultivation practices can affect disease or pest incidence are as follows:
- Rapid changes in environmental conditions (e.g. reduced temperature) may slow plant growth and increase the risk of seedling damping-off and of damage by sciarid fly larvae in a range of herb crops.
- Over-watering and water-logging increase the risk of Pythium, Phytophthora and Rhizoctonia root rots, sciarid flies, shore flies, slugs and snails on a range of herb crops.
- Factors such as fertiliser/pesticide scorch, nutrient deficiencies/excesses, soft growth, and mechanical damage at harvest can predispose plants to infection by B. cinerea.
- Poorly growing plants or those with soft growth can be more susceptible to attacks by pests such as aphids.
Growers of soil-cultivated protected herbs may need to consider methods of soil disinfestation in order to reduce the risk of soil-borne diseases, and for effective weed control. Soil disinfestation is rarely needed for pest control, although it may be advised by PHSI if an outbreak of a quarantine leaf miner species has occurred, as leaf miner pupae can survive in the soil. Serious diseases that can build up in the soil include root rots caused by Phytophthora species, Pythium species and Rhizoctonia solani, Sclerotinia rot, white rot (Sclerotium cepivorum) and wilts caused by Fusarium oxysporum and Verticillium dahliae. As methyl bromide is no longer permitted as a pre-plant soil treatment, herb growers must now determine which alternative soil disinfestation methods are most suitable for their crops and production systems. HDC Factsheet 09/07 ‘Soil disinfestation options for cut flower crops’ provides detailed information that is of relevance to protected, soil-grown herbs, with advice on assessment of soil disinfestation need and choice of appropriate chemical or physical treatment. In general, the need for soil disinfestation is high following a serious outbreak of a soil-borne disease or weed, particularly when the next crop is susceptible to the same problem (e.g. Sclerotinia rot on a range of crops).
Chemical options include the use of either dazomet (as Basamid) or metam-sodium (e.g. Discovery) as pre-planting soil sterilants. Both products give good control of a wide range of pathogens, some insect pests, nematodes and annual weeds. Dazomet is usually applied by a contractor although some growers apply the product themselves. Metam-sodium is a relatively easy treatment for growers to apply themselves.
Physical treatments include the use of steam applied to soil by a range of methods (sheet steaming, steam plough or vacuum steaming) for soil disinfestation. Soil steaming can match methyl bromide in its broad spectrum of activity and efficacy, although treatment to depth can be difficult to achieve. An advantage is that the soil can be re-planted in just a few days. Disadvantages are the relatively high cost compared with chemical fumigation, and the high-energy use.
Another physical treatment of relevance to protected herb production (including herbs produced to organic standards) is the use of propane (LPG)-fired burners that can be used for disinfestation of the soil surface. The method is effective for killing weeds, pathogens and pests near the soil surface (top 1-2 cm of soil) and depends on minimal soil disturbance before the next crop. It may also be used for destroying surface crop debris that may harbour pests and pathogens. In particular, flaming of perennial crops such as mint in autumn can substantially reduce the risk of rust carry-over to the next season.
Physical pest exclusion methods
Physical methods can be used for excluding some flying pests:
- Screening doors and vents with insect-proof mesh can prevent immigration of flying pests such as moths, leaf miner adults and thrips adults, but proper insect screening is expensive and reduces ventilation unless fans are also used. Opening doors or vents or using door screens at selected times over the 24-hour period may help to exclude specific pests, if information is available on whether the pests fly by day or night. For example, many moth pests of protected herbs are noctuids, that fly by night, e.g. angle shades and silver Y moth. Thus keeping doors and vents closed or screened during the night can help to exclude these species. However, this strategy would not be appropriate for all moth species, e.g. the mint moth that flies during the day.
- Use of regular sticky traps, or long ‘roller’ traps can be useful to trap incoming pests, or for trapping pests such as whiteflies, sciarid flies and winged aphids in heavy infestations. They can be used in pest ‘hotspots’, next to doors or under vents, between infested crops and new batches of plants, or in empty structures after an infested crop has been removed. However, they can also catch flying biological control agents so they should be positioned and timed with care.
- Use of fine-meshed crop covers can minimise crop invasion by pests such as flea beetle adults. However, covers need to be in place before pest activity starts, and susceptible soil-grown crops should not follow previous host crops if the possibility of beetles emerging from plant debris under the covers is to be avoided.
Biological pest and disease control
Biological control agents available in the UK
There is a wide range of biological control agents for pest management available in the UK that are suitable for use on protected herbs, including predators, parasitic wasps, insect-parasitic nematodes, entomopathogenic fungi and bacteria. Details of the appropriate biological control agents to consider when planning a biological control programme for each herb crop are given in each best practice guideline in Section B.
Planning biological control programmes
The use of biological control agents within an IPM programme will vary according to the herb production system used, the herb crop grown and each grower’s own requirements and individual nursery conditions. Each programme needs to be planned carefully, taking into account the pests likely to occur on each crop, the time of year, environmental conditions in the glasshouse or polythene tunnel and the range of cultural methods and compatible pesticides likely to be used with the biological controls. Growers of all-year-round pot herbs use a comprehensive biological control programme throughout the year, whereas growers of cut or pot herbs in unheated glasshouses or polythene tunnels often use a more limited range of biological control agents, only in the spring to autumn period. IPM consultants and biological control suppliers can help to plan programmes tailored for the conditions on each individual nursery, such as the appropriate combinations of biological control agents to use, and recommended release rates and frequency.
Legislation regarding use of biological control agents
Most biological control agents used in the UK are native, or have become established in the UK after being imported, and thus their release is not subject to legislation. Examples of native biological control agents are the aphid parasitic wasps, Aphidius colemani and Aphidius ervi, and the entomopathogenic nematode, Steinernema feltiae, used for control of sciarid flies and thrips. An example of biological control agents native to other countries but now established in the UK is the predatory mite Phytoseiulus persimilis, used for spider mite control. This predator was imported to Europe from Chile in 1958 and has since become established in many countries including the UK.
There are, however, two types of biological control agents that are subject to legislation in the UK:
Non-indigenous biological control agents that are not yet established in the UK
Defra import and release licences are needed for the use of non-indigenous biological control agents that are not yet established in the UK. The biological control suppliers apply for the licences before they make such agents commercially available for use. The licence will be subject to certain conditions, such as releasing the organism only in fully-protected structures (glasshouses or fully-covered polythene tunnels). Examples of currently-available biological control agents subject to Defra release licences are the predatory mite Amblyseius swirskii, used for thrips and whitefly control, Neoseiulus californicus, used for spider mite control and the parasitic wasp, Eretmocerus eremicus, used for whitefly control. These three organisms may currently only be released in fully protected structures. Further details of these biological control agents are given in B.3, B.5, B.6 and B.9.
Microbiological control agents
Biological control agents classed as microbiological control agents are fungi and bacteria. These ‘biopesticides’ are currently subject to the same legislation as pesticides in the UK, i.e. they have to be approved by the Chemicals Regulation Directorate (CRD) before they can be made commercially available. There are currently only three entomopathogenic fungi; Verticillium lecanii, used for whitefly control, Beauveria bassiana, used for whitefly and thrips control and Metarhizium anisopliae, which has an EAMU for use on herbs for control of sciarid fly larvae and thrips pupae. One bacterium (Bacillus thuringiensis, used for caterpillar control) is approved in the UK. Further details of these biological control agents are given in B.5, B6 and B.7.
Biological control of diseases and natural products
As for biopesticides, ‘biofungicides’ are subject to the same legislation as pesticides in the UK, i.e. they have to be approved by the Chemicals Regulation Directorate (CRD) before they can be made commercially available. The use of biological control as a component of integrated disease management has not been as extensively researched as biological pest control, but UK approvals for biofungicides have increased in recent years. Contans® WG (containing Coniothyrium minitans), is available for the management of Sclerotinia sclerotiorum on edible and non-edible crops (Section C.8). A product called Serenade ASO based on the bacterium Bacillus subtilis is now registered as a biological fungicide for use on UK crops for control of a range of diseases including Botrytis and powdery mildews. Newer examples in the UK include AQ10 (Ampelomyces quisqualis) for powdery mildew control and Prestop products (Gliocladium catenulatum) for management of fungal root rots. Modes of action for biofungicides vary with products but include parasitism, niche displacement or by triggering plant defence responses.
Pesticides as a component of IPM
Integrated pest and disease management on protected herbs may occasionally require the use of pesticides, e.g. to reduce pest numbers so that biological control can then continue. Similarly, fungicide use may be warranted where for example, newly planted batches of pot herbs are at high risk of infection from downy mildew already present on neighbouring batches. Tables 2 and 3 list pesticides and fungicides that are currently approved (March/April 2013) for the control of pests and diseases on protected herbs.
Compatibility with IPM
If a pesticide is needed within IPM, it should be selected carefully to minimise adverse effects on biological control agents. Each pesticide may have different effects on different biological control agents and on their various life stages. Full details of the compatibility of pesticides with biological control agents are available from biological control suppliers and from the following websites: www.biobest.be and www.koppert.com. If as a last resort, a pesticide harmful to biological control agents has to be used, it can often be restricted to pest or disease ‘hotspots’ to limit any impact on biological control agents.
Maximum residue levels
For pesticides that are liable to leave residues in foodstuffs, even when used correctly, statutory limits known as Maximum Residue Levels (MRLs), have been established. MRLs are not safety limits but rather provide a check that products have been used as directed. A spreadsheet of MRLs applicable to different crops can be found on the website of the Chemicals Regulation Directorate (CRD) at www.pesticides.gov.uk. Minimisation of pesticide residues requires constant attention by herb growers. The situation for herbs is complex and not all herb species have the same MRLS for the same pesticide. Residue accumulation can vary in different herb species, and with multiple harvests from one crop and differing harvest intervals according to time of year. Growers should be aware that MRLs have been set at the limit of detection for a wide range of active ingredients. Although many of these may not be approved on herbs, they must not be found in herbs for example, as a result of previous crop applications or drift from elsewhere. Guidelines for minimising pesticide residues can be found in the Assured Produce protocol for culinary herbs at www.assuredproduce.co.uk.
When planning use of pesticides in an IPM programme, full account should be taken of any pest or disease resistance issues. Some of these issues are highlighted in Tables 2 and 3.
The Insecticide Resistance Action Group (IRAG) and the Fungicide Resistance Action Group (FRAG) publish detailed advice and leaflets on resistance management, which can be obtained from the CRD website (www.pesticides.gov.uk). Use of IPM as described in Section A can reduce reliance on pesticide use, thus decreasing resistance risk.
Pesticide resistance is known to occur in many pest species that could occur on UK protected herbs, e.g. aphids, leaf miners, spider mites, thrips and whiteflies. Not all pest populations of the same species will have the same resistance status on every nursery, or every year. For example, the peach-potato aphid could be resistant to the carbamate pesticide pirimicarb (e.g. Aphox) on one nursery, but susceptible to this pesticide on another, whereas the melon and cotton aphid will always be resistant to pirimicarb on all nurseries. Both these aphid species are currently susceptible to the aphid antifeedant pymetrozine (Chess WG) and the neonicotinoid pesticides, thiacloprid (e.g. Calypso) and acetamiprid (e.g. Gazelle SG). It is essential to follow Insecticide Resistance Management (IRM) guidelines, to preserve the effective life of pesticides for as long as possible. For example, specific IRM guidelines are given on neonicotinoid pesticide product labels and EAMU sheets. These guidelines recommend using no more than two applications of any neonicotinoid insecticides on any crop, and alternating insecticides from a different chemical group with a different mode of action, so that two successive applications of a neonicotinoid are not made.
Fungicide resistance can develop gradually, resulting in partial loss of control, for example with actives from the dicarboximide group (e.g. grey mould resistance to iprodione on a range of crops). There are other instances of rapid and complete loss of control (e.g. races of lettuce downy mildew that are resistant to metalaxyl). More recently, there have been cases in the UK and overseas of fungal resistance to the QoI or strobilurin fungicide group (e.g. azoxystrobin). To minimise the likelihood of resistance developing, application of strobilurin fungicides should be made with due regard to current FRAG-UK guidelines for Qol compounds. These recommend that strobilurins should be used as part of a programme in a mixture with a fungicide from a different cross-resistance group, and that no more than two applications of strobilurin fungicides should be made.
When planning pesticide use for control of pests or diseases, key points for resistance management are as follows:
- Only use a pesticide if necessary.
- Do not rely on repeated use of one pesticide as this will hasten the development of resistance.
- Alternate pesticides with different modes of action from different chemical groups.
- Make as full a use as possible of fungicides with a multi-site mode of action, which are less prone to fungicide resistance problems.
- Use products as directed on the label and/or the EAMU (previously EAMU) sheet, in order to optimise efficacy, in particular ensuring correct dose, timing and suitable environmental conditions.
- Avoid repeated applications of very low doses.
- For diseases that multiply rapidly, a single early preventative fungicide treatment when conditions are high risk for disease development may reduce the need for several later sprays.
- Be aware of ongoing resistance problems, check any advisory information within relevant EAMUs and seek professional assistance if there are cases of unexplained poor control following pesticide applications.
Legislation regarding pesticide use
Only approved pesticides may be used on any crop. Following withdrawal of the Long Term Arrangements for Extension of Use from 31 December 2006, pesticides for use on protected herbs are available as On-Label Approvals, Extension of Authorisation for minor Uses (EAMUs, previously SOLAs) or Commodity Substance Approvals. Some pesticides are currently exempt from the pesticide regulations as they act by physical means.
Producers of ornamental herbs should note that only those pesticides with full On-Label Approval or EAMU for edible herbs, or those currently exempt from the regulations should be applied to ornamental herbs.