Microsoft
FINAL REPORT
To:
Horticultural Development Council
Bradbourne House
Stable Block
East Malling
Kent
ME19 6DZ
AYR tomato production:
Phase 1 of the development and implementation
of a robust IPM programme
May 2007
_____________________________________________________________________
Commercial – In Confidence
Project Title: AYR tomato production: Phase 1 of the development and
implementation of a robust IPM programme
Project number: PC 251
Project leader: Dr R. Jacobson, IPM Consultant
Report: Final report, May 2007
Principal experimental
worker: Dr R. Jacobson
Other contributors: Ms L. Aitken, Syngenta Bioline
Mr M. Burton, Wight Salads Ltd
Ms J Eldridge, Wight Salads Ltd
Mr T. Mills, Mill Nurseries Ltd
Mr B. Moralee, Wight Salads Ltd
Ms G. Rochester, J. Baarda Ltd
Locations of Project: J. Baarda Ltd,
Belasis Park, Billingham, Teeside, TS23 4HR
Library facilites at Lancaster University.
Mill Nurseries,
Ottringham Rd, Keyingham, Humberside, HU12 9RX
Wight Salads Ltd,
Arreton, Isle of Wight, PO30 3AR
HDC Project Co-ordinator: Mr D. Hargreaves, Horticultural Consultant
Date Commenced: 1 January 2006
Date completion due: 30 April 2007
Key words: Tomato, all year round production, supplementary lighting, integrated pest management, biological pollination
Whilst reports issued under the auspices of the HDC are prepared from the best available information, neither the authors nor the HDC can accept any responsibility for inaccuracy or liability for loss, damage or injury from the application of any concept or procedure discussed.
The contents of this publication are strictly private to HDC members. No part of this publication may be copied or reproduced in any form or by any means without prior written permission of the Horticultural Development Council.
The results and conclusions in this report are based on information gathered from the scientific and horticultural literature, study tours to the Netherlands and Finland, and crop monitoring at three commercial sites in the UK. The conditions under which the studies were carried out and the findings have been reported with detail and accuracy. However, because of the biological nature of the work it must be borne in mind that different circumstances and conditions could produce different results. Therefore, care must be taken with the interpretation of the results especially if they are used as the basis for commercial product recommendations.
Authentication
I declare that this work was done under my supervision according to the procedures described herein and that this report represents a true and accurate record of the results obtained.
Signature………………………………………………………………………….
Dr R. J. Jacobson
Project Manager
IPM Consultant,
5 Milnthorpe Garth, Bramham, West Yorks, LS23 6TH
Tel: 07752 874162
E-mail: rob.jacobson@tiscali.co.uk
Date …………….
CONTENTS
Page
Grower Summary
Headlines 5
Background and expected deliverables 5
Summary of work to date 6
Financial benefits to growers 9
Action points for growers 10
Science Section
Part 1: General introduction to project
1.1. Background 11
1.2. Overall aim and specific objectives 12
1.3. Approach 12
1.4. Financial implications 13
Part 2. Features of AYR growing regimes that could influence IPM
2.1. Principle differences between AYR and conventional tomato
production 14
2.2. General responses of insects and mites to light 15
2.3. Potential impact of AYR production and artificial
lighting on IPM 17
Part 3. Pollination
3.1. Background 19
3.2. Examination of tomato flower development and pollen
availability in an artificially lit tomato crop 21
Part 4. Crop monitoring
4.1. Introduction 27
4.2. The sites 27
4.3. Specific questions 28
4.4. Monitoring methods 28
4.5. Site 1. Mill Nurseries 29
4.6. Site 2. Wight Salads Ltd 30
4.7. Site 3. John Baarda Ltd 35
4.8. Summary of findings 38
4.9. Summary of conclusions 41
References 42
Acknowledgements 46
GROWER SUMMARY
HEADLINE
Integrated control of leaf miner and caterpillars was achieved over the winter months for an all year round tomato crop. A successful biological pollination strategy using bees was also developed. Future work will focus on refining the use of Macrolophus caliginosus as IPM agent to and management of populations to prevent plant damage.
BACKGROUND AND EXPECTED DELIVERABLES
British tomato growers and retailers share the common goal of pesticide-free crop production. Prior to the start of this project, supplies of home-grown glasshouse produce were only available between late January and October, leaving a gap of three winter months to be filled by produce imported from southern Europe. The latter are grown under considerable pressure from invading pests and most of the growers are still dependent on intensive pesticide applications to supply produce of the quality demanded by the UK market. The potential risk of chemical residues being detected in tomatoes on supermarket shelves during the winter period is therefore greater than during the rest of the year. As a consequence, retailers have encouraged UK growers to develop methods of producing tomatoes all year round (AYR) using artificial lighting when natural light is limiting coupled with reduced or pesticide free production.
AYR production and artificial lighting can affect the behaviour of both herbivorous and beneficial insects / mites directly via light intensity, photoperiod and spectral range, and indirectly via the plant due to changes in the glasshouse climate, agronomic practice, plant nutritional status and plant defence mechanisms. As a consequence, there was little doubt that the IPM and pollination programmes currently used by British tomato growers would have to be modified for use in AYR cropping. However, Macrolophus caliginosus bred under artificial lights throughout the winter and suppressed population of whiteflies, leafminers and spidermites.
The overall aim of this project was to develop and implement robust IPM and biological pollination programmes that would provide reliable results under artificial lights in AYR tomato crops in the UK.
The project was designed with two distinct phases. The first phase was rapid information gathering from all available sources; i.e. literature searches, study tours and detailed crop monitoring. This enabled the initial IPM and biological pollination programmes to be modified very quickly. Throughout the first phase of the project, any abnormal behaviour by pests, beneficial insects and bumble bees was noted and the programmes were fine tuned to overcome such difficulties. Any persistent difficulties identified were to be addressed by more in depth investigation in the second phase of the project.
The three partners involved in this project represented the majority of British tomato growers who were producing AYR crops under artificial lighting at the start of the 2005/06 growing season. Their total AYR tomato crop area was approximately 12.1 hectares with an estimated value of over £9m. The sites presented three quite different scenarios:
• Mill Nurseries, Ottringham Rd, Keyingham, Humberside, HU12 9RX
This site consisted of 1.8ha of modern glass, which was the entering the second year of AYR cropping in a geographical area of moderate pest pressure.
• Wight Salads Ltd, Main Road, Arreton, Isle of Wight, PO30 3AR
This site consisted of 1ha of converted glass, which started AYR production in November 2005 in a geographical area of high pest pressure.
• J. Baarda Ltd, Belasis Business Park, Billingham, Teeside, TS23 4HR
This site consisted of 9.3ha of new purpose built glass with the first crops being planted between November 2005 and January 2006. This geographical area had no history of glasshouse crop production and was of low pest pressure.
SUMMARY OF WORK TO DATE
Preliminary studies:
The information gathered from the preliminary literature searches, contact with overseas IPM practitioners and study tours to Finland and the Netherlands indicated several ways in which IPM and biological pollination could be affected by AYR production and artificial lighting. These affects could be advantageous or disadvantageous:
Possible advantages:
• Inter-planting crops provides continuous production runs which could result in long-term stable relationships between pests and beneficial species.
• The performance of parasitoids in glasshouse crops is normally restricted by low temperatures and short days in the early season. However, this may not be the case in crops with artificially extended days if the intensity and spectrum of artificial light is adequate to enable the parasitoids to search efficiently.
• Pest species (e.g. spider mites) and beneficial species (e.g. Orius majusculus) that enter a resting phase known as diapause during the winter under natural conditions should breed continuously in AYR crops and it should not be necessary to restart the biological programme each new season.
• Changes in the duration and intensity of light can have an impact on plant biochemistry and morphology, leading to an increase in resistance to pests. However, such changes could also impair the activity of natural enemies.
Possible disadvantages:
• AYR production may create an additional pest control challenge because there will be no extended period when the glasshouse is empty and can be thoroughly disinfested.
• Unsubstantiated reports from Finland suggested Encarsia formosa were attracted to the high pressure sodium lamp (HPS) units where they were killed by the hot bulbs.
• Continuous illumination can negatively affect dusk / dawn active or night-active insects such as Feltiella acarisuga.
• The lights could attract certain pests (e.g. moths and possibly plant bugs) into the glasshouse, thus creating additional problems in the late summer and autumn.
• Spider mites breed more successfully than their predators in the tops of plants during hot weather and this often leads to control failures in the summer. It was anticipated that this could occur at other times of the year in crops receiving artificial light from above due to vertical temperature and humidity gradients.
• Bumble bees may become disorientated under HPS lamps due to the lack of natural UV light.
Pollination studies:
During a study tour to Finland, it was noted that many tomato growers who used bumble bees for pollination did not expect the colonies to remain active for more than 2-3 weeks (i.e. compared to 8-12 weeks in a conventional crop grown in the summer in the UK). The colonies rapidly became depleted because the adult bees failed to return to the hives and the immature bees died of starvation. Given this experience and contradictory information from the Netherlands, the partners in this project decided to instigate their own practical study to develop a system that would be best suited to their needs. The study was done in late January / early February 2005 in a tomato crop (cv Temptation) which was artificially lit (15,000lux) from midnight to 17.00hrs. Natural light was available from about 07.45 to 17.00hrs. Flower opening and pollen flow was monitored over a 24 hour period and the implications in terms of bumble bee activity were determined.
The results showed that pollen flow began 5-6 hours after the lights were switched on and continued for a further 8-9 hours, indicating that the correct biological pollination strategy was to release bumble bees when natural light became available (in this case from about 08.00hrs) and close the hives before natural light became limiting (in this case from about 15.00hrs). This information was adopted with caution because we were aware that other cultivars may behave differently and that pollen flow in cv Temptation may be different under other environmental conditions. However, this approach became the basis of the biological pollination strategy in the UK study crops throughout the 2006/07 winter and was successful in a range of tomato types and cultivars.
Although opening and closing hives manually was time consuming, the labour cost was acceptable considering the benefits that could be gained from reliable biological pollination. The task may be simplified in the future by automated remote controlled systems. However, it remains to be seen whether the cost of such installations can be justified.
Monitoring pests and natural enemies:
Dedicated staff were employed to record numbers of specific pests and natural enemies at regular intervals between mid-autumn and early-spring. The sampling was done at fixed sample stations so that population trends could be monitored over time.
In addition, crop workers were trained to recognise the common pests, pest damage and natural enemies and were instructed to immediately report any new pest incidence or significant changes in existing pest populations. The key findings are listed below.
Encarsia were released at weekly intervals throughout the project at higher rates than in conventional crops. Although parasitised whitefly scales could be found in all the crops, they rarely exceeded 30% of the whole whitefly population and did not keep the pest under control. This was entirely consistent with experiences in Finland where it was reported that Encarsia adults were attracted to the HPS lamp units and killed by the hot bulbs. While this may have been the case where lamps were hung vertically among plants in Finnish crops, we found no evidence of pest or beneficial species being killed on bulbs positioned above UK crops. We currently have no explanation as to why Encarsia performed so poorly in the lit crops and must now decide whether to persevere with this parasite or concentrate on other control measures that have given more promising results.
A large leafminer infestation developed in one of the monitored crops in November and December 2006. A total of 2.5 Diglyphus parasitoids were released per m2 in November. The parasitoids established very quickly and the leafminer population crashed within a few weeks. Although this was a very worrying period in terms of potential crop damage, the final results showed beyond any doubt that Diglyphus could be very effective under these environmental conditions.
Spider mites were found throughout the winter and there was no evidence of them entering diapause under the artificial lights. We can therefore conclude that the biological control programme against spider mites will be continuous and will not have to be restarted each spring.
The spider mite population growth was generally constrained by Macrolophus and / or occasional applications of spiromesifen (Oberon) against whiteflies. As a consequence, suppression of spider mites did not depend on Phytoseiulus and the anticipated breakdown in biological control in the tops of the plants was not encountered in any of the monitored crops. One objective for the future will be to improve biological control of whiteflies, which will reduce the need to apply spiromesifen during the autumn and winter. This will clearly have a knock-on effect on spider mite population growth and we can anticipate having greater dependence on biological control in the future. Therefore, our inability to control spider mites with Phytoseiulus in the tops of the plants may assume greater importance in the future.
There is no doubt that many species of moths are attracted to illuminated glasshouses when it is otherwise dark outside. However, for the moths to be attracted and gain entry to the glasshouse, the lights must be switched on at the same time as the ventilators are open, which doesn’t usually happen during natural darkness. Crops are commonly ventilated to rapidly reduce temperature during the “pre-night” period but the risk of moths being attracted into the glasshouse at that time is relatively small because the lights are switched off. When the lights are turned back on at around midnight, black out screens are drawn to prevent light pollution and so the attraction to moths is greatly reduced. It is unusual for ventilators to be open during that period of natural darkness but it does happen under some circumstances; e.g. on mild nights the heat from the lamps may raise the air temperature above the set point thus triggering the ventilators and black out screens to open by about 10% to allow air exchange. In fact, only one serious problem occurred with caterpillars and this may have originated from moths that invaded during the summer. This population of tomato looper caterpillars was successfully controlled with repeated applications of Bacillus thuringiensis. If growers wish to entirely exclude moths, then it will be necessary to screen glasshouse ventilators at a cost of £80k to £100k per hectare depending on the type of structure (but should note that this may influence aspects of environmental management).
This project has shown that Macrolophus will continue to breed under artificial lights throughout the winter and will produce very large populations if there is sufficient invertebrate prey. Furthermore, they appear to be capable of suppressing whitefly, leafminer and spider mite populations throughout the winter. Until recently this may have caused concern to AYR tomato growers because Macrolophus will cause extensive damage to tomato trusses after they have killed the invertebrate prey. However, a method of culling Macrolophus populations with applications of natural pyrethrins has recently been developed in another HDC project (PC 201) and this has greatly reduced the risk of the predators causing economic damage to the crop.
These results indicate that Macrolophus has the potential to form the basis of an IPM programme in AYR tomato crops. In the future, we must learn how to optimise the beneficial effects of this predator and fine tune the methods of culling the population to prevent plant damage.
FINANCIAL BENEFITS TO GROWERS
In Finland, biocontrol programmes in crops with artificial lighting were reported to be 1.5-2.6 times more expensive than conventional crops. This was acceptable in that country because the Finnish public were willing to pay a premium for home-grown produce. However, it was unlikely that British growers would receive such a premium and it was vitally important that IPM costs were kept within acceptable parameters. It was calculated that if this project could keep the additional IPM costs at the lower end of the above range, then the consortium could save more than £7.7k per hectare or £93.2k over the whole AYR production area during the first season. That would provide a very rapid payback time for the project.
ACTION POINTS FOR GROWERS
The specific objectives of the first phase of this project were to gather information about IPM and biological pollination programmes in AYR crops by searching the scientific and horticultural literature, liaising with overseas research workers and IPM practitioners, embarking on study tours to Scandinavia and the Netherlands, and monitoring the partners’ commercial crops. In addition, we were to identify weaknesses in the existing IPM and biological control programmes that would be addressed in phase two of the project.
The following findings were of immediate benefit to the partners in the project:
• Biological pollination is effective in illuminated tomato crops during the winter if the bumble bees are released when natural light becomes available in the morning but confined to their hives before it becomes limiting in the afternoon.
• The parasitic wasp, Diglyphus, established in tomato crops under HPS lamps in mid-winter and successfully controlled a large leafminer population. However, the cost was relatively high.
• Macrolophus bred under artificial lights throughout the winter and suppressed populations of whiteflies, leafminers and spider mites at one site.
• Overall, infestations of caterpillars were less common than anticipated. Tomato looper caterpillars were troublesome at one site but were successfully controlled with repeated applications of Bacillus thuringiensis.
• Spider mites continued to breed on tomato plants throughout the winter under HPS lamps.
The following subjects should be further investigated in phase two of the project:
• We are currently unable to explain why Encarsia performed so poorly in the lit crops and must now decide whether to persevere with this parasitoid or concentrate on other control measures that have given more promising results against whiteflies.
• As biological control of whiteflies is improved and applications of spiromesifen (Oberon) are reduced, we can anticipate having a greater requirement for biological control of spider mites by Phytoseiulus and / or Macrolophus. Depending on the relative efficacy of these two predators, the possibility of a breakdown in control of spider mites by P. persimilis in the tops of the plants may have to be further investigated.
• Macrolophus has the potential to form the basis of an IPM programme in AYR tomato crops. We must now learn how to optimise the beneficial effects of this predator during the winter and fine tune the methods of culling populations (e.g. with natural pyrethrins) to prevent plant damage.
SCIENCE SECTION
PART 1: GENERAL INTRODUCTION TO PROJECT
1.1. Background
British tomato growers and retailers share the common goal of pesticide-free crop production. Prior to this project, supplies of home-grown glasshouse produce were only available between late January and October, leaving a gap of three winter months to be filled by produce imported from southern Europe. The latter were grown under considerable pressure from invading pests and most of the growers were dependent on intensive pesticide applications to supply produce of the quality demanded by the UK market. The potential risk of chemical residues being detected in tomatoes on supermarket shelves during the winter period was therefore greater than during the rest of the year. As a consequence, retailers were encouraging UK growers to develop methods of producing tomatoes all year round (AYR) using artificial lighting when natural light was limiting.
In the early 2000s, some of the more adventurous British tomato growers planned large investments in new and upgraded facilities for AYR production to enable them to satisfy this increasing demand for uninterrupted supplies of top quality, completely traceable, home-grown produce. However, it was clear that these ventures would only be successful if the pesticide usage could be maintained at a minimal level through effective IPM.
British tomato growers have led the world in the reduction of pesticide use through IPM (Jacobson, 2004). These highly advanced IPM programmes have been developed over 30 years and include control measures that can be employed against over 10 individual species of pests. With so many control measures being used simultaneously, the overall programmes are complex and can be difficult to manage successfully. If just one of the control measures fails and it becomes necessary to use a non-specific insecticide, the whole programme can be disrupted.
It was known that artificial lighting could affect the behaviour of both herbivorous and beneficial insects / mites directly via light intensity, photoperiod and spectral range, and indirectly via the plant due to changes in the greenhouse climate, agronomic practice, plant nutritional status and plant defence mechanisms (Vanninen & Johansen, 2005). As a consequence, there was little doubt that the IPM and pollination programmes currently used by British tomato growers would have to be modified for use in AYR cropping. Vanninen & Johansen (2005) stated that very little research had been completed on the specific impact of artificial lighting on IPM. However, there was a growing wealth of practical experience among growers and IPM practitioners in Scandinavia and the Netherlands. This project was planned to utilise several approaches to gathering information quickly and thus help British tomato growers through the early stages of this new venture.
1.2. Overall aim and specific objectives
The overall aim of the project was to develop and implement robust IPM and biological pollination programmes that would provide reliable results under artificial lights in AYR tomato crops in the UK.
The specific objectives were to:
• To gather information about IPM and biological pollination programmes by:
1. Searching the scientific and horticultural literature.
2. Liaising with overseas research workers and IPM practitioners.
3. Study tours to Scandinavia and the Netherlands.
4. Monitoring commercial crops throughout a complete growing season.
5. Modifying programmes in line with findings during the growing season.
• To identify weaknesses in the existing IPM and biological control programmes.
• To design appropriate experimental programmes to address those weaknesses (to begin in the next phase of the project).
• To communicate the results to the UK tomato industry.
1.3. Approach
There was no doubt that the British tomato industry faced a steep learning curve regarding the use of IPM and biological pollination under artificial lighting in AYR cropping systems. There was also no doubt that the required techniques would have to be developed and implemented very quickly if the new growing regimes were to be financially successful.
The partners involved in this project represented the majority of British tomato growers who were producing AYR crops under artificial lighting in the 2005/06 growing season. They presented three quite different scenarios:
• Mill Nurseries (Humberside) – 1.8 ha of modern glass entering the second year of of AYR cropping in an area of moderate pest pressure.
• J. Baarda Ltd (Teeside) – 9.3 ha of new purpose built glass starting production in November 2005 in an area of low pest pressure.
• Wight Salads Ltd (Isle of Wight) – 1.0 ha of converted glass starting production in November 2005 in an area of high pest pressure.
The project was designed with two distinct phases. The first phase was to be one of rapid information gathering from all available sources; i.e. literature searches, study tours and detailed crop monitoring. This would enable the initial programmes to be modified very quickly. It would also identify those subjects which would require more in depth investigation in the second phase of the project.
Throughout the first phase of the project any abnormal behaviour by pests, beneficial insects and bees would be noted. Where possible, the programme would be fine tuned to overcome such difficulties and all changes would be recorded to benefit other growers. Persistent difficulties would be identified and addressed in the second phase of the project.
1.4. Financial implications
At the start of this project, it was known that the value of AYR tomato crops would vary according to many factors but conservative estimates suggested that it would be at least £180k per ha greater than conventionally grown crops. The total value of the AYR crops being grown by this consortium was therefore estimated to be approximately £9m. However, the margins would be relatively small and all costs would have to be tightly controlled.
In Finland, biocontrol programmes in crops with artificial lighting were reported to be 1.5-2.6 times more expensive than conventional crops (Backman, 2002). This had been acceptable in that country because the Finnish public were willing to pay a premium for home-grown produce. However, it was unlikely that British growers would receive such a premium and it was vitally important that IPM costs were kept within acceptable parameters. It was calculated that if this project could keep the additional IPM costs at the lower end of the above range, then the consortium could save more than £7.7k per hectare or £93.2k over the whole AYR area during the first season. That would provide a very rapid payback time for the project.
PART 2. FEATURES OF AYR GROWING REGIMES THAT COULD INFLUENCE IPM
2.1. Principle differences between AYR and conventional tomato production
Before considering the potential impact of AYR production and supplementary lighting on IPM, it will be useful to list the principle differences between AYR and conventional season tomato production:
• The most obvious difference is that the glasshouse always contains plants.
• Inter-planting is now common practice in AYR crops, which means there are often plants of different ages being grown in close proximity (e.g. Figure 1).
• The plants’ illuminated day varies from site to site but is usually extended with high-pressure sodium (HPS) lights to provide 16-18 hours of light. To take advantage of off-peak electricity tariffs, the artificial lights are commonly switched on at some point between 22.00hrs and 02.00hrs. Thus, the plants day would typically begin at midnight and continue until 17.00hrs.
• In any crop, the quality and quantity of light will vary during the growing day and at different times of the year. However, this is most pronounced in the AYR growing regime in mid-winter when all light may be supplied from HPS lamps for up to ten hours of the day. The study sites were equipped to provide between 10,000 and 25,000 lux of photosynthetically active radiation (PAR) (125 and 300 μmol m-2 s-1) at variable levels. The spectral range of the HPS lamps emit wavelengths of light largely between 400 and 700nm but dominated by yellow (560-600 nm) and red (mainly 600-640 nm) (Spaargaren, 2001).
Figure 1. A recently inter-planted crop showing new plants growing alongside the mature crop.
[pic]
• The study sites all had HPS lamps mounted above the crop although it is quite common in Scandinavia to have a proportion of the lamps suspended vertically between the plants. The overhead positioning of the lamps can result in vertical temperature gradients with increased temperature and reduced humidity in the top of the crop canopy (Both et al., 2002).
• Normal mains electricity causes lights to flicker at a frequency of about fifty times per second. The human eye sees this as uninterrupted light but it can be visible to many insect species and may influence flying behaviour (e.g. Shields 1980; Shields 1989).
2.2. General responses of insects and mites to light
Light affects the behaviour of both herbivorous and beneficial insects / mites directly via light intensity, photoperiod and spectral range and indirectly via the plant due to changes in the greenhouse climate, agronomic practice, plant nutritional status and plant defence mechanisms. The subject is extremely complex and some of the literature is contradictory. This section attempts to summarise the range of responses of insects and mites to light and in doing so draws heavily upon an excellent and concise review of the subject by Vanninen and Johansen (2005) and a more specific review of the effect of light on plant defence mechanisms by Roberts and Paul (2005). The subsequent section (2.3) attempts to predict the impact that some of these factors could have on IPM under artificial lights.
Direct effects of light on insects and mites
Insects can be sensitive to wavelengths between about 250-730 nm (UV to red light) (Wigglesworth, 1972). The light receptors (i.e. compound eyes, ocelli, stemmata) in most insect species have sensitivity peaks around 350 nm (UV), 450-490 nm (blue/blue-green) and 520-600 nm (green-yellow) (Frazier, 1985; Young et al., 1987; Mellor et al., 1997). A few species are sensitive into the 600-700 nm region (orange-red) (Shields, 1989) but there is no evidence for visual responses to infrared light (Wigglesworth, 1972; Young et al., 1987).
The responses of insects to the spectral range vary depending on the species (Frazier, 1985). The spatial and spectral properties of an insect’s eye are often directly linked to the behaviour and habitat of that animal (Peitsch et al., 1992; Stavenga, 1992). The adaptive strategies in terms of photoreception and visually mediated behaviour of day-active and night-active insects are often contrasted (Frazier, 1985); for example UV-light is the most effective spectral area for attracting nocturnal insects (Blomberg et al., 1976) while many diurnal beneficial species prefer other wavelengths (e.g. Nabli et al., 1999).
Spectral quality is important for insect behaviour such as host and habitat location both in herbivores (Dethier, 1963; Vaishampayan et al., 1972; Shields, 1989; Matteson & Terry, 1992; Shoonhoven et al., 1998) and parasitoids / predators (Wardle, 1990; Brown et al., 1998). Many species disorientate when UV-radiation is removed from the environment (Antignus, 2000). Polarized light can also play a role in insect orientation although the mechanism is poorly understood (Pomozi et al., 2001). The effects of the general light environment on the foraging process of insects is modified by both factors extrinsic (e.g. plant species, canopy structure, host availability, humidity, host-associated cues) and intrinsic (e.g. insect species, population size, nutritional status, mating status, dispersal status,) (Dethie, 1963; Wigglesworth, 1972; Wäckers, 1994; Brown, 1998; Heinz & Parrella, 1998; Molck et al., 1999; Bellamy & Byrne, 2001; Blackmer & Cross, 2001).
Photoperiod affects the onset of arthropod diapause, reproduction, feeding and movement activity in many species-specific ways (e.g. El-Banhawy, 1977; Babiker, 1978; van Houten & Veenendaal, 1990; Smith & Rutz, 1991; Brodsgaard, 1994; Veerman, 1994; Tommasini & Nicoli, 1995; Auger et al., 1999). The photoperiodic responses of arthropods may be modified by light quality and intensity, temperature, life stage, heritage, adaption to different environments, and nutritional status of food plants (Danilevskii, 1965). Bemisia tabaci serves as an example of how complex the effects of photoperiod and light intensity on different life-stages can be; for example high light intensities and long photoperiod improve the egg hatch of B. tabaci, whereas survival of immatures is affected by photoperiod but not by light intensity (Blackmer et al., 2002).
Indirect effects via the plant:
The four-way interactions between growing environment, plant, herbivorous invertebrate and natural enemies are multifaceted and extend across many different temporal and biological scales. These complex interactions range from a molecular to ecological-scale and may be of short or long term duration. While the details of these complex interactions are beyond the scope of this study at this phase, it is important to be aware that they exist should they need to be taken into account at a later stage.
In plants, light quality and / or quantity affects the biomass formation, sugar concentrations and pigment synthesis (Boo et al., 2002). Long-term use of continuous light in tomato and sweet pepper results in the accumulation of assimilates in leaves, as plants cannot fully export these products of photosynthesis out of leaves unless a sufficiently long dark period is provided (Demers & Gosselin, 2002). The impact of such factors on herbivore development is complex and poorly understood.
Some aspects of herbivore resistance in plants correlate positively with light intensity although resistance differences of cultivars often even out in intensive light (de Kogel et al., 1997). High light intensity can result in changes in the structural defence mechanisms of tomato, with harmful consequences to some natural enemies (Nihoul, 1993) but also to pest reproduction (Berlinger & Dahan, 1987). Tomato plants grown in full sunlight produce tougher leaves with higher concentrations of allelochemicals and lower concentrations of protein, resulting in reduced growth rates of some herbivores (Berlinger et al., 1983; Jansen & Stamp, 1997). Continuous artificial light from HPS lamps causes leaf chlorosis in plants lacking effective photoprotective pigments (Demers & Gosselin, 2002). The synthesis of plant phenolics, commonly considered classic defence compounds against herbivores (but see Close & McArthur, 2002 for critique of this assumption) increases in high intensity light.
Roberts and Paul (2005) brought together evidence that illustrated that light not only modulates plant defence responses via its influence on biochemistry and plant development but, in some cases, is essential for the development of resistance. Their conclusions consider the impact of light on plant defence and suggest conceptual models that explain these observations in terms of both the molecular and the ecophysiological responses to light and invertebrate herbivory.
2.3. Potential impact of AYR production and artificial lighting on IPM
The information summarised in sections 2.1 and 2.2 suggests several ways in which we may anticipate IPM in tomato crops being affected by AYR production and artificial lighting. These affects could be advantageous or disadvantageous.
Possible advantages:
By inter-planting crops, it may be possible to take advantage of more continuous production runs to achieve more stable equilibria between pests and beneficial species. The latter could open new opportunities for biological control in glasshouses because it would be more comparable to permanent and semi-permanent agro-ecosystems (Jacobson, 2005).
It has long been known that the performance of parasitoids in glasshouse crops is restricted by low temperatures and short days in the early season (e.g. Parr et al., 1976). This should not be the case in crops with artificially extended days if the intensity and spectrum of artificial light is adequate to enable the parasitoids to search efficiently (e.g. van Lenteren et al., 1992; Jander, 1962).
Pest species (e.g.. spider mites [Tetranychus urticae]) and beneficial species (e.g.. Orius majusculus) that exhibit photoperiodic diapause under natural conditions should breed continuously in AYR crops. It may be argued that this would be beneficial because the biological control programme would be continuous and it should not be necessary to reintroduce the beneficial species each new season.
Changes in the duration and intensity of light can have an impact on plant biochemistry and morphology, which can influence invertebrate performance. For example, Nihoul (1993) reported that the density of trichomes varied on tomatoes under different light conditions and this has been shown to have effects on both T. urticae and its predator, Phytoseiulus persimilis (Croft et al., 2005). Such effects could in themselves be advantageous or disadvantageous.
Possible disadvantages:
AYR production may create an additional pest control challenge because there is no extended period when the glasshouse is empty and can be thoroughly disinfested.
There are as yet unsubstantiated reports from Finnish growers of Encarsia formosa being attracted to and killed by the hot bulbs in the HPS lamp units (Vanninen & Johansen, 2005; Murmann, 2002).
Continuous illumination can negatively affect dusk / dawn active or night-active insects like Feltiella acarisuga (Vanninen & Johansen, 2005).
The lights could attract certain pests (e.g. moths and possibly plant bugs) into the glasshouse, thus creating additional problems in the late summer and autumn.
It is known that spider mites breed more successfully than their predators in the tops of plants during hot weather and this can result in control failures in the summer. This may be anticipated at other times of the year in crops receiving artificial light from above, where vertical temperature and humidity gradients exist (Both et al., 2002).
In crops that require biological pollination, the activity of bumble bees may be impaired under HPS lamps due the bees becoming disorientated. This is most likely to occur on dull days between November and February when there is very little natural UV light in the glasshouse.
PART 3. POLLINATION
3.1. Background
The yield of the tomato plant is determined by both the number and weight of individual fruits. Therefore, high yields are dependant on proper fruit set and development (Ho & Hewitt, 1986). The mechanisms of flowering and fruit development have been comprehensively reviewed (e.g. Hayward, 1938; Wittwer & Aung, 1969; Picken, 1984; Picken et al., 1985; Atherton & Harris, 1986; Atherton & Rudich, 1986; Ho & Hewitt, 1986) and are beyond the scope of this report. However, it has long been recognised that poor pollination is a major cause of incomplete fruit set and the production of undersized fruits (Picken, 1984). In particular, Picken made reference to the effects of low light on carbohydrate deficiency and the development of pollen during the winter months in the UK. In this study, we made the initial assumption that light would not be limiting to satisfactory flower and pollen production due to the provision of adequate supplementary light throughout the winter (Spaargaren, 2001).
Despite the production of pollen throughout the winter, its transfer from anther to stigma is likely to be inefficient and will usually benefit from some form of physical assistance (Picken, 1984). For many years, growers mechanically vibrated each flower around mid-day when the pollen was believed to flow most freely. However, this was a labour intensive and therefore expensive operation. Furthermore, the timing was not always correct and the results were sometimes disappointing.
Leading UK growers began commercial-scale trials using bumble bees as pollinators in 1989. By 1992, bumble bees were being used in virtually all long-season tomato crops. The savings in terms of labour compared to hand pollination and the increased yields obtained from improved fruit set had made this the most rapidly adopted new technology in the recent history of UK horticulture. The increased financial pressures that have since been placed on growers mean that the benefits of biological pollination are now a prerequisite to any successful tomato production system in the UK. Consequently, when UK growers began to look at AYR production, it was clear that bumble bees must be made to work as effectively in the artificially lit winter crops as in conventionally grown summer crops.
Bumble bees perceive ultraviolet (UV) radiation (Kevan et al., 1991; Kevan et al., 2001) and require this for orientation and navigation. In particular, bumble bees utilise patterns of UV absorbance / reflectance from petals (Lanau, 1992) and without it their visual recognition of flowers is seriously impaired.
UV light has wavelengths from 100 to 380nm and consists of UVA, UVB and UVC (Spaargaren, 2001). The latter is filtered out by the atmosphere and does not penetrate to the earth’s surface. Very little UVB is transmitted through the types of glass most commonly used in commercial greenhouses. The natural UV light that does reach commercial tomato crops is therefore largely UVA and it is this which is so important to bumble bees for orientation and navigation.
The study crops in this project utilised HPS lamps which emit wavelengths of light largely between 400 and 700nm, i.e wavelengths that are not commonly believed to be perceived by bumble bees. In experiments in artificial situations using plastic model flowers, Dyer and Chittka (2004) observed that bumble bees perceived changes when UV radiation was either included or excluded from the illumination source and concluded that the bees rapidly learned to find the model flowers in either illumination environment. This conclusion implied that poor performance of bumble bees would be relatively short-lived in artificially lit tomato crops because they would rapidly adapt to the alien environment. However, this has not been substantiated by observations in commercial crops in northern Europe (e.g. Murmann, 2002).
During a study tour to Finland in February 2006, it was noted that many tomato growers who used bumble bees for pollination did not expect the colonies to remain active for more than 2-3 weeks; i.e. compared to 8-12 weeks in a conventional crop grown in the summer in the UK. The colonies were rapidly depleted because adult bees failed to return to the hives and immature bees died of starvation. To maintain biological pollination in their crops, the Finnish growers frequently replaced the hives at considerably greater expense than in a conventional summer crop (Murmann, Ronnqvist, Vanninen pers comm., 2006).
Two articles on this general subject were published in the Dutch horticultural journal “Groenten and Fruit” on 18 November 2004 and 10 March 2005. The origin of this information has not been confirmed beyond doubt and so the articles will be cited in this report as of anonymous authorship. The first of the articles stated quite clearly that tomato flowers opened approximately two hours after it became light (be that natural or artificial light) and remained open for only a “number of hours”. As bumble bees did not fly in artificial light, it was concluded that if the lights came on too early (say midnight), there would be too few hours when both the flowers were open and the bees were active to give effective pollination. The overall conclusion was not to use artificial lights before 06.00hrs. However, this would not have been financially acceptable to UK growers who depended on buying off-peak electricity at reduced price. Another conclusion from the first article was to place hives above the level of the lamps during winter months. However, this was very inconvenient at times when the life of the colony could be quite short and regular monitoring was essential.
The second article in Groenten and Fruit revised some of these recommendations. For example, it was now concluded that hives placed above lamps were no more effective than those placed 2m above the ground. It was also acknowledged that growers had to use the lights for more hours per day than previously recommended in order to make the most of their investment. In other words, they could not wait until after 0600 hours to switch on their lights. Other new recommendations were to use larger bumble bee colonies and to place coloured flags above hives to help the bees to find their way home. An automatic opening / closing system was also introduced that would allow remote control of the entrances to hives (see section 3.2 and Figure 10).
Given the poor results with biological pollination in Finland and the contradictory information from the Netherlands, the partners in this project decided to instigate their own practical study to develop a system that would be best suited to their needs. As stated above, it was necessary to use the artificial lights from around midnight in order to take advantage of lower tariffs for electricity. The study therefore monitored flower opening and pollen flow over a 24 hour period from the start of illumination and determined the implications of this in terms of bumble bee activity.
3.2. Examination of tomato flower development and pollen availability in an artificially lit tomato crop
Materials and method:
The study was done late January / early February 2005 in Block 15 at Wight Salads (WS) Main Road Site. The crop was artificially lit (15,000lux) from midnight to 17.00hrs. Natural light was available from about 07.45 to 17.00hrs. The bees were held within the hives on this day so that pollen flow would not be affected by their activity.
Twenty tomato plants (cv Temptation) were marked and the uppermost trusses inspected at intervals of 1-2 hours throughout the day (i.e. 00.30, 02.30, 03.30, 05.00, 06.30, 08.00, 10.00, 12.00, 14.00 and 16.30 hours). On each occasion, the following were recorded:
• Numbers of set fruit
• Numbers of flowers closed (including flowers that had been open the previous day but closed overnight).
• Numbers of flowers open with visiting marks.
• Numbers of flowers open without visiting marks.
• Numbers of flowers starting to break open for the first time.
The degree to which the flowers were open (i.e. expressed as % reflexed) was also recorded.
Pollen flow was checked from open flowers at each assessment by tapping flowers ten times over a black surface. It was recorded on a scale of 0 (no pollen visible) to 5 (copious quantities). This was done using equivalent trusses / flowers on plants close to each assessment point. Pollen viability was not checked at that stage but was inferred by follow up assessments which checked that the fruit had successfully set.
Environmental conditions (temperature, HD and natural light) were recorded from the environmental control computer.
Results and discussion:
The key events listed chronologically were:
• All flowers were closed during the dark period (e.g. Figure 2).
• Flowers that had previously been visited by bees were first to open. Most were 30-50% reflexed by 02.30hrs (Figure 3) and completely open by 03.30hrs (Figure 4). These flowers had no discernable pollen flow.
• The flowers that had previously been open but had not yet been visited by bees were 10-30% reflexed by 02.30hrs (Figure 3), 20-50% reflexed by 03.30hrs (Figure 4) and 50-80% reflexed by 05.00hrs (Figure 5). A very small number of flowers were releasing small quantities of pollen at 02.30hrs but the majority still had no pollen flow at 05.00hrs (Figure 6).
• At 06.30hrs, the majority of the flowers that had previously been open but not visited by bees were fully reflexed and were producing moderate quantities of pollen (index 2-3 on scale; average c2.2). The time between the lights being switched on and there being reasonable pollen flow was therefore 5 - 6.5 hours. It would be these flowers that would be most attractive to the bumble bees during the course of the day.
• By 08.00hrs, the average pollen flow in the flowers that had previously been open had increased to index 2.4.
• New flowers (i.e. flowers that had not previously been open) began to break open at 03.30hrs and by 05.00hrs there was one such flower (10-20% reflexed) on about half of the trusses. This increased to 60% of trusses by 06.30hrs and 85% by 08.00hrs. However, their progress in terms of reflexation was slow.
• Apart from a slight increase in pollen flow (index 2.6), there was very little change in any of the parameters being monitored between 08.00 and 10.00hrs.
• At midday, the main change was that the older flowers, which had already been visited at the start of the day, were closing and falling off. The new flowers had hardly changed in terms of reflex since 08.00hrs and were not releasing any pollen. However, the quantity of pollen had increased again in the most active flowers and it now ranged from index 2 to 4 (average c3.5).
• By 14.00hrs, pollen flow was starting to slow down. Some plants were releasing none, while others released reduced quantities. The flow now ranged from index 0 to 3 (average 2).
• By 16.30pm, pollen flow had stopped completely in most flowers. A few still were still releasing at index 1-2 but the overall average was index 0.3.
The availability of pollen recorded from cv Temptation under these growing conditions is summarised in Figure 6.
Plant and air temperatures are shown in Figure 7, light levels inside and outside the glasshouse are sown in Figure 8, and humidity deficit (HD) is shown in Figure 9. There were no sudden changes relating to any of these factors that could have triggered the start of pollen flow around 05.00hrs.
Conclusions:
The information gathered from this study showed that pollen flow coincided with the natural day and indicated that the correct biological pollination strategy should be to release bumble bees when natural light became available (in this case from about 08.00hrs) and close the hives before natural light became limiting (in this case from about 15.00hrs). This information was adopted with caution because we were aware that other cultivars may behave differently and that cv Temptation may behave differently under different environmental conditions. However, this approach became the basis of the biological pollination strategy in the UK study crops throughout the 2006/07 winter and was successful in a range of tomato types and cultivars.
Although opening and closing hives manually is time consuming, the labour cost is acceptable considering the benefits that are gained from reliable biological pollination. The task may be simplified in the future by automated remote controlled systems (e.g. Figure 10). However, it remains to be seen whether the cost of installation can be justified.
Figure 2: A typical truss at 12.45hrs (lights came on between 12.00 and 12.15am)
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Figure 3. A typical truss at 02.45hrs
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Figure 4: A typical truss at 03.45hrs
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Figure 5: A typical truss at 05.00hrs
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Figure 6. Summary of pollen flow from midnight to 17.00 hrs on 1 February 2006 (based on a scale of 0-5)
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Figure 7. Plant and air temperature during the experimental period (i.e. from 00.00hrs to 23.59hrs on 1 February)
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Figure 8. Light levels inside and outside the glasshouse the experimental period (i.e. from 00.00hrs to 23.59hrs on 1 February)
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Figure 9. Humidity deficit in the glasshouse during the experimental period (i.e. from 00.00hrs to 23.59hrs on 1 February)
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Figure 10. Example of a remote controlled door bee hive door
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PART 4. CROP MONITORING
4.1. Introduction
Although part of the remit of this project was to search the scientific and horticultural literature for relevant information about the impact of AYR production on IPM, Vannninen and Johansen (2005) had already stated that very little specific research had been completed on this subject and so we knew that we would have to generate new information ourselves.
Initial IPM programmes were designed with the growers and their biocontrol suppliers. Wherever possible, monitoring systems were put in place to record information about pests, beneficial insects and biological pollination. The Project Leader visited the sites at appropriate times to examine the crops and study the monitoring records in liaison with the growers and biocontrol suppliers. Any abnormal behaviour by pests, beneficial insects and bumble bees was noted and, where possible, the programme was fine tuned to overcome the difficulties. Persistent problems were identified so that they could be addressed in the second phase of the project.
4.2. The sites
The three partners involved in this project represented the majority of British tomato growers who were producing AYR crops under artificial lighting at the start of the 2005/06 growing season. Their total AYR tomato crop area was approximately 12.1 hectares, with an estimated value of over £9m. The sites presented three quite different scenarios:
Site 1.
Mill Nurseries, Ottringham Rd, Keyingham, Humberside, HU12 9RX
This site consisted of 1.8ha of modern glass, which was the entering the second year of AYR cropping in a geographical area of moderate pest pressure.
Site 2.
Wight Salads Ltd, Main Road, Arreton, Isle of Wight, PO30 3AR
This site consisted of 1ha of converted glass, which started AYR production in November 2005 in a geographical area of high pest pressure.
Site 3.
J. Baarda Ltd, Belasis Business Park, Billingham, Teeside, TS23 4HR
This site consisted of 9.3ha of new purpose built glass with the first crops being planted between November 2005 and January 2006. This geographical area had no history of glasshouse crop production and was of low pest pressure.
4.3. Specific questions
In addition to the general observations, the crop monitoring addressed the following specific questions:
1. How effective are Encarsia formosa against glasshouse whitefly (Trialeurodes vaporariorum) populations on tomato plants under HPS lamps?
2. Are E. formosa populations suppressed because individuals are being attracted to and killed by HPS lamps?
3. Do spider mites (Tetranychus urticae and T. cinnabarinus) diapause in autumn / winter under artificial lights or do they breed continuously throughout the winter?
4. Do spider mites respond to the temperature and humidity gradient by congregating in the tops of plants under artificial lights while Phytoseiulus persimilis stay lower down plant?
5. Are species of moths with caterpillars capable of feeding on tomato plants) attracted into the crops by the artificial lights?
6. In unlit conventional season crops, we would expect to see a natural decline in numbers of Macrolophus caliginosus during the early autumn - does this also happen in AYR crops?
7. Do Diglyphus isaea remain active and continue to suppress leafminer (Liriomyza bryoniae) populations during the winter?
4.4. Monitoring methods
General pest monitoring:
All crop workers were trained to recognise the common pests, pest damage and natural enemies, and were instructed to immediately report any new pest incidence or significant changes in existing pest populations. It was considered very important to react to this information as quickly as possible and to allow the procedures detailed below to evolve to take into account any new hot spots of pest activity.
Quantifiable pest / beneficial monitoring:
In addition to the above, dedicated staff were employed at sites 2 and 3 to count numbers of specific pests and natural enemies at regular intervals between mid-autumn and early-spring. The counts were done at fixed sample stations and each consisted of three marked plants. The number of sample stations varied between sites but remained consistent in each crop so that population trends could be plotted against time. It must be stressed that the intention was to monitor trends over time rather than determine precise numbers of insects in the crops. The following procedures were followed:
Macrolophus
The numbers of M. caliginosus adults and nymphs were recorded on each plant at each sample point by examining (or beating over a white tray) one leaf positioned 5-6 down from the growing point.
Whitefly
Adults: At each sample point, the numbers of adult whiteflies were recorded in the tops of the plants.
Scales: The stratum of crop within which the whitefly scales were developing was determined on each occasion (approximately leaf position 9-10). The numbers of scales were then recorded on one appropriate leaf per plant.
Parasitised scales: The stratum of crop within which the parasitised scales were clearly black was determined on each occasion (approximately leaf position 12-13). The numbers of black scales and the numbers of white scales (usually empty at this stage) were recorded and the proportion parasitised was calculated.
Leafminer
The stratum of crop within which the majority of mines were active was determined on each occasion. This was variable depending on the cultivar and the time of year. The numbers of leafminer larvae that had been attacked by D. isaea and M. caliginosus was also recorded.
Spider mites
Monitoring of spider mites and P. persimilis was less formal, with observations based on localised populations reported by crop workers.
Other pests
Information was gathered about other less common pests as and when they occurred in the crops.
In all cases, the average numbers were calculated and plotted on a chart.
4.5. Site 1. Mill Nurseries
Mill Nurseries had been growing AYR tomato crops since late 2004 and had greater experience than the other two partners when this collaboration began. The manager kindly shared his experiences from those first two winters (i.e. 2004/05 and 2005/06) even though much of his work had been done before the official start of this project. A lit crop had been planned at Mill Nurseries for the winter of 2006/07 but it wasn’t planted due to unexpected complications with marketing arrangements. As a consequence, the formal crop monitoring work that had been planned in this project for the winter of 2006/07 at Mill Nurseries could not be done. The following notes are based on the managers own records from the winters of 2004/05 and 2005/06.
The crops grown during that period were all cv Ruby Red, which is exclusive to Mill Nurseries. This is a baby plum tomato with very sweet fruit (typical Brix value 8). The main inter-plant was done in August 2005 with the older crop being terminated in late September 2005.
The lighting installation was capable of delivering up to 15,000lux. The operating regime differed between the winters of 2004/05 and 2005/06. In the first winter, the lights were typically switched on at 23.00hrs and used for up to 18 hours per day. They were switched off during the day when natural light reached a threshold of 250 watts/m2. In the second winter, the manager used his experience to make decisions on a daily basis, manipulating the lighting and heating regimes according to his own interpretation of the crop growth and fruit load. Using this approach, he increased yield while reducing energy inputs compared to the previous year.
The fruit was set using physical pollination techniques rather than biological pollination from the end of October to early April in each season.
The main pest problems were caused by the tomato looper (Chrysodeixis chalcites) and glasshouse whitefly. Large populations of tomato looper caterpillars were present throughout the first winter (2004/05) and caused considerable damage to foliage and fruit. There was a second flush of activity in a cherry tomato crop on the same site during the summer of 2005 and a further invasion of the lit crop in September 2005. This is not a common pest of tomatoes in the UK. It occurs only sporadically and usually on nurseries near the east coast. It was eventually controlled on this site with repeated spray applications of Bacillus thuringiensis (Dipel DF).
Glasshouse whiteflies appeared to be under control with biological control agents until the new plants were brought into the glasshouse in August 2005. Adult whiteflies then migrated to the younger plants and quickly became established to produce potentially damaging populations. Encarsia formosa were present but were not controlling the pest as the crop progressed into the early winter. Eventually, the manager resorted to spray applications of the insect growth regulator, buprofezin (Applaud), in the top half of the crop, followed by spiromesifen (Oberon) throughout the crop. The pest population then remained at an acceptable level for the rest of the winter.
There were very few spider mites or leafminers present in the crops during either winter, which was attributed to effective treatments of abamectin (Dynamec) applied each autumn. The application of spiromesifen (Oberon) against whiteflies will have contributed to the control of any spider mites that were present in the crop at that time.
4.6. Site 2. Wight Salads Ltd
Wight Salads Ltd first used lights in autumn 2005 over a crop that had been inter-planted in August 2005, which meant there had been continuous cropping in that glasshouse since November 2004. Detailed crop monitoring began in November 2005 and continued throughout that winter until the lights were switched off in April 2006. Further inter-planting was done in March and August 2006. Crop monitoring began again in mid-October 2006 and continued until the lights were switched off in April 2007. Throughout the entire period, half of the glasshouse contained cv Temptation (vine ripened classic) and the other half contained cv Campari (vine ripened large cocktail).
Bumble bees were used for pollination from the start of AYR cropping and this was backed up by manual techniques until February 2006. Following the study reported in section 3 of this report, the new bumble bee management strategy was adopted and manual pollination ceased. Fruit set was satisfactory throughout the entire period.
Winter 2005/06
The results of crop monitoring through the winter of 2005/06 are shown for M. caliginosus and whitefly / parasitised scales in Figures 11 and 12 respectively.
Encarsia formosa were released in the glasshouse at weekly intervals throughout the project. As at Mill Nurseries, whiteflies appeared to be under control until the new plants were brought into the glasshouse in August 2005. Adult whiteflies then migrated from the mature crop to the younger plants and quickly established potentially damaging populations. The normal release rates of E. formosa were boosted from 0.5m2/wk to 6m2/wk but it became necessary to apply spiromesifen (Oberon) at the beginning of November (week 44). This resulted in a significant reduction in the number of adult whiteflies. The whitefly population then remained stable at a non-damaging level for the rest of the winter (Figure 12), which was attributed to the combined constraints provided by both E. formosa and M. caliginosus during that period.
Figure 12 shows that E. formosa were present throughout the winter. The weekly assessments of levels of parasitism varied between 25% and 34% from November to mid-January, and thereafter improved slightly to between 35% and 42% until mid-April.
There was a decrease in the total numbers of M. caliginosus after the application of spiromesifen (week 44) (Figure 11), which was largely due to the reduction in the numbers of nymphs. It is recommended that the impact of this chemical on M. caliginosus nymphs should be further investigated in parallel project. Thereafter, the M. caliginosus population remained stable until monitoring ceased in April.
There were very few spider mites present in the crop throughout the monitoring period which was attributed to the application of spiromesifen at the start of the winter. Leafminers were present throughout the winter but only in very small numbers, their population growth being suppressed by M. caliginosus.
In summary, once the initial whitefly migration to the new plants had been controlled, the full range of pests was suppressed throughout the winter by biocontrol agents. With hindsight, and with the benefit of information from the winter of 2006/07, we believe that it was M. caliginosus that made the major contribution to this satisfactory situation.
Figure 11
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Figure 12
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Winter 2006/07
The results of crop monitoring through the winter of 2006/07 are shown for M. caliginosus, whitefly / parasitised scales and leafminers in Figures 13, 14 and 15 respectively.
This year began differently to 2005/06 in that the whitefly population was under control but the M. caliginosus population was large and some damage to trusses was detected in early October. Previous experience indicated that this situation could lead to substantial financial losses unless the M. caliginosus population was significantly reduced. Based on recent work (Jacobson & Morley, 2006), the whole crop was sprayed with natural pyrethrins (Pyrethrum 5EC). However, this treatment was probably applied too thoroughly and it reduced the numbers of M. caliginosus to a level at which they no longer provided a constraint to the whitefly or leafminer population growth. There followed a very rapid increase in the size of the whitefly and leafminer populations (Figures 14 and 15).
The initial response to the leafminer infestation was to release relatively large numbers of D. isaea parasitoids in the crop. A total of 2.5 D. isaea were released per m2 in November. The parasitoids established very quickly and the leafminer population crashed within a few weeks (Figure 15). Although this had been a very worrying period in terms of potential crop damage, the final results showed beyond any doubt that D. isaea parasitoids could be very effective under these environmental conditions.
With the experience from 2005/06, the normal release rates for E. formosa were increased from 0.5m2/wk to 2m2/wk. Although these parasitoids were present in the crop throughout the autumn, they did not prevent an explosion in whitefly numbers during November / December and it finally became necessary to apply spiromesifen (Oberon) at the end of December. The impact on the whitefly population was quite spectacular (Figure 15).
The invertebrate prey provided by the leafminer and whitefly populations inevitably led to resurgence in the numbers of M. caliginosus in the crop (Figure 13). Although the population stabilised after the application of spiromesifen, in the absence of adequate invertebrate prey the M. caliginosus turned their attention on the plants and started to cause damage to the flowers and fruit. There was no alternative but to cull the population with another application of natural pyrethrins in late January. However, on this occasion, the spray was restricted to upper half of the plants and this allowed sufficient M. caliginosus to survive to continue to effect a satisfactory degree of control upon the other major pests. All pests then remained at an acceptable level for the remainder of the winter.
Spider mites were detected in small numbers throughout the winter. Their failure to build up into damaging populations was attributed to the combined effect of M. caliginosus predators and spiromesifen applied in December.
The events in the crops at this site during the winters of 2005/06 and 2006/07 illustrated the importance of M. caliginosus to the pest control programme. In the future, we must learn how to obtain the beneficial effects of this predator and how to effectively cull the population before they cause damage to the plants.
Figure 13
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Figure 14
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Figure 15
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4.7. Site 3. John Baarda Ltd
The first glasshouses were completed at this facility at Belasis Park, Billingham in early Autumn 2005 and the first two crops were planted at the end of October 2005. The remaining crops were all in place by mid-January 2006. As this was a new facility, there were no residual pest populations in the structures and the plants remained substantially free from pest infestation until the summer of that year.
Biological pollination began in mid-November when the first flowers started to show. Although there was no formal crop monitoring done on-site at that time, the biocontrol supplier’s report on 5 January 2006 indicated that hives were being left permanently open and the colonies were only lasting approximately three weeks (Aitken, unpublished data). Biological pollination was being supplemented with manual pollination as necessary to ensure good fruit set. This situation was consistent with information gleaned from Finnish growers at about the same time. The biological pollination strategy was changed during January / February 2006 and hives were then opened at 08.00hrs and closed at 15.00hrs each day. This task took one person one hour to complete across the whole nursery and so the last hives to be visited were actually open from 09.00 to 16.00 hrs. In addition, the colonies were provided with supplementary food in the form of dried pollen cake. For the remainder of the winter, bumble bee colonies were active for 5-7 weeks and biological pollination was satisfactory.
Encarsia formosa and Eretmocerus eremicus were released in the glasshouse at weekly intervals through most of the project.
The lights were switched off in April 2006. Pests gradually became established in the crops during the summer of 2006 and by the time the lights were switched back on in the autumn there were localised infestations of glasshouse whitefly, spider mites and leafhoppers (species to be confirmed). In addition, leafminers were detected on young plants delivered from the propagator in September for the inter-plant (Aitken, pers. com.). Macrolophus caliginosus had been released and were becoming established in some crops.
Formal monitoring began in November 2005 in two 1.5ha glasshouses; block B with cv Piccolo and block C with cv Jessica. The results of crop monitoring through the winter of 2006/07 are summarised for M. caliginosus, whitefly / parasitised scales and leafminers in block B in Figures 16, 17 and 18, and in block C in Figures 19, 20 and 21 respectively.
The insect population trends were broadly similar in each block. Numbers of glasshouse whiteflies increased rapidly during through December 2006 (Figures 17 and 20) and this became the most important issue of the winter. There were very few M. caliginosus present in these crops through November / December (Figures 16 and 19) and the level of parasitism by E. formosa and E. eremicus was generally poor (Figures 17 and 20). The whitefly populations were eventually controlled by an intensive spray programme in late-January / early-February 2007 using a range of products with complementary modes of action. Unfortunately, this programme also depleted numbers of whitefly natural enemies and these had to be reintroduced from mid-February.
The leafminer populations (Figures 18 and 21) and spider mite populations remained small throughout the monitored period. The latter was probably helped by spiromesifen (Oberon) applied against whiteflies.
Figure 16
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Figure 17
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Figure 18
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Figure 19
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Figure 20
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Figure 21
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4.8. Summary of findings
This section uses the information gathered during the course of this study to address the specific questions asked in section 4.3 of this report.
4.8.1. How effective are E. formosa against whitefly populations on tomato plants under HPS lamps?
Encarsia formosa were released at weekly intervals at sites 2 and 3 throughout the project. The numbers released were always at least as large as in a typical conventional crop and at some times very much greater (e.g. during 2005/06 at Site 2 and during February 2007 at Site 3). This report will not dwell on the actual numbers released as the author believes that these were often insignificant compared to the numbers being generated within the crop (Figures 14, 17 and 20).
Whitefly scales parasitised by E. formosa could be found in all the crops throughout the monitoring periods. However, the percentage of scales parasitised was usually quite low and rarely exceeded 30% before mid-January. These results were consistent with reports from Finland (Murmann, 2002).
We currently have no explanation why E. formosa performs so poorly in the lit crops. However, the objectives of this project were to identify weaknesses in the existing IPM / biological control programmes and to design appropriate experimental programmes to strengthen those aspects of the overall control strategy. We must now decide whether to persevere with E. formosa or concentrate on other control measures that have given more promising results (section 4.8.7).
4.8.2. Are E. formosa populations suppressed because individuals are attracted to and killed by the HPS lamps?
Prior to this project, Finnish growers and consultants had reported that E. formosa adults were attracted to and killed by the hot bulbs in the HPS lamp units (Vanninen & Johansen, 2005; Murmann, 2002) although this had never been proven beyond doubt. During a study tour to Finland in February 2006, Howlett and Jacobson observed large numbers of dead adult whiteflies on HPS bulbs hanging vertically within a crop (Figure 22) but were unable to find any dead E. formosa.
During winter 2006/07, over 30 used HPS bulbs were examined after replacement at Site 2 (Figure 23). These bulbs had all been positioned over the crop during the whitefly problems of late Autumn 2006. No pests or beneficial insects were found on any of the bulbs.
There is no irrefutable evidence that this is the cause of poor E. formosa establishment. To further investigate this issue, specific experiments will have to be conducted in which known numbers of parasites are released in sealed compartments containing an HPS bulb.
Figure 22. Dead adult whiteflies on an HPS bulb hanging vertically among plants in a Finnish tomato crop.
[pic]
Figure 23. Examples of used bulbs from Site 2 which were examined for presence of dead E. formosa
[pic]
4.8.3. Do spider mites diapause in autumn / winter under artificial lights or do they breed continuously throughout winter?
Spider mites were found throughout the winter at Sites 2 and 3 and there was no evidence of them entering diapause where the artificial lights were used. We can therefore conclude that the biological control programme will be continuous and will not have to restart in the spring.
4.8.5. Do spider mites respond to the temperature and humidity gradient by congregating in the tops of plants under HPS lamps while P. persimilis stay lower down the plant?
Spider mites breed more successfully than P. persimilis in the tops of plants during hot weather, which often results in biological control failures in conventional crops during the summer. It was anticipated that the same effect may be seen during the winter in crops receiving artificial light from above.
In fact, the spider mite population growth was generally constrained by M. caliginosus and / or applications of spiromesifen (Oberon) against whiteflies. As a consequence, suppression of spider mites did not depend on P. persimilis and the anticipated breakdown in biological control was not encountered in any of the monitored crops.
One objective for the future will be to improve biological control of whiteflies, which will reduce the need to apply spiromesifen during the autumn and winter. This will clearly have a knock-on effect on spider mite population growth and we can anticipate having greater dependence on biological control by M. caliginosus and P. persimilis. Depending on the relative importance of these two predators, the possibility of a breakdown in control of spider mites by P. persimilis in the tops of the plants may have to be further investigated.
4.8.6. Are species of moths (with caterpillars capable of feeding on tomato plants) attracted into the crops by the artificial lights?
There is no doubt that many species of moths are attracted to illuminated glasshouses when it is otherwise dark outside. However, for the moths to be attracted and gain entry to the glasshouse, the lights must be switched on at the same time as the ventilators are open, which doesn’t often happen during natural darkness. Crops are commonly ventilated to rapidly reduce temperature during the “pre-night” period (i.e. during the late afternoon / early evening) but the risk of moths being attracted into the glasshouse at that time is relatively small because the lights are switched off some time before the ventilation occurs. When the lights do come on at around midnight, black out screens may be drawn to prevent light pollution and so the attraction to moths is greatly reduced. It is unusual for ventilators to be open during that period of natural darkness but it does happen under some circumstances; e.g. on mild nights the heat from the lamps may raise the air temperature above the set point thus triggering the ventilators and black out screens to open by about 10% to allow air exchange. To be sure of preventing invasion by adult moths the glasshouse ventilators would need to be screened with insect proof netting at a cost of £80k to £100k per hectare depending on the type of structure.
The only serious problem with moths occurred at Site 1 in 2004 and 2005. However, this may have originated from an invasion of the tomato looper moth during the summer so that the grower was in fact combating a resident population rather than continuous re-invaders which were being attracted by the lights.
In summary, moths are attracted to the illuminated glasshouses but there has been less invasion and establishment in AYR crops than anticipated. This risk may be entirely prevented by screening glasshouse ventilators at a cost of about £80k to £100k per hectare. Alternatively, the supplementary lighting and ventilation regimes can be synchronised to reduce ventilators opening during lighting periods and the crop can be closely monitored and any infestation of caterpillars controlled with spray applications of Bacillus thuringiensis.
4.8.7. Is there a natural decline in numbers of M. caliginosus in AYR crops during the early autumn?
This project has shown that M. caliginosus will continue to breed under artificial lights throughout the winter and will produce very large populations if there is sufficient invertebrate prey. Furthermore, they appear to be capable of suppressing whitefly, leafminer and spider mite populations throughout the winter.
4.8.8. Do Diglyphus isaea remain active and continue to suppress leafminer populations through the winter and into the following spring?
The experience at site 2 in 2006/07 showed that D. isaea are capable of breeding successfully under artificial lights and controlling large leafminer populations during the winter. However, the experience at site 2 in 2005/06 suggests that they may not be required if the M. caliginosus population is maintained at a sufficiently large level.
4.9. Summary of conclusions
• Glasshouse whitefly proved to be the most difficult pest to keep under control at all sites.
• The parasitic wasps, E. formosa, established in all crops under HPS lamps but failed to provide satisfactory control of the whitefly populations.
• The parasitic wasps, D. isaea, established in crops under HPS lamps in mid-winter and successfully controlled the leafminer population.
• Macrolophus caliginosus bred under artificial lights throughout the winter and suppressed populations of whiteflies, leafminers and spider mites.
• Infestations of caterpillars were less common than anticipated but tomato looper did cause difficulties at one site. They were successfully controlled with B. thuringiensis.
• To exclude moths entirely, glasshouse ventilators would need to be screened.
• Spider mites continued to breed on tomato plants throughout the winter under HPS lamps.
• The efficacy of P. persimilis was masked by treatments applied against whiteflies which also suppressed the spider mite populations. This pest / predator interaction may have to be further investigated when biological control of whiteflies under HPS lamps is perfected.
• Macrolophus caliginosus has the potential to form the basis of an IPM programme in AYR tomato crops. In the future, we must learn how to optimise the beneficial effects of this predator and how to more effectively cull the population (e.g. with natural pyrethrins) before they cause damage to the plants.
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ACKNOWLEDGEMENTS
The author is extremely grateful to Tony Mills (Mill Nurseries), Paul Howlett / Brian Moralee (Wight Salads Ltd), and Tim Haworth / Phil Thompson (J. Baarda Ltd) who provided unlimited access to their crops and without whose co-operation this project would not have been possible. Further thanks are due to Linda Aitken (Syngenta Bioline) and Mark Jones (BCP Ltd) for sharing information, John Frame / Jonathon Barker (Enza Zaden UK) for organising the study tour to the Netherlands, Irene Vanninen / Tom Murmann for providing a very interesting study programme in Finland, and to Derek Hargeaves for critical analysis of the draft report. My special thanks are due to Josie Eldridge / Max Burton (Wight Salads Ltd) and Gillian Rochester (J. Baarda Ltd) who showed tremendous dedication throughout their crop monitoring and presented very clear and concise data sets at the end of their practical work.
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