Report of an outbreak of Thrips palmi in Southern England, April 2000 – July 2001
Background
1. In April 2000, a Plant Health and Seeds Inspector (PHSI) based at the Chichester office, West Sussex, detected orange-coloured thrips during a routine inspection of a crop of all-year round chrysanthemums, produced principally for sale to supermarkets. The producer had installed traps, suspended above the crop, to monitor the presence of established thrips species, particularly Western western Flower flower thrips (Frankliniella occidentalis). The inspector sent one of these traps to the Central Science Laboratory (CSL) for diagnosis and Thrips palmi was confirmed.
2. The nursery had two large glasshouse areas close to each other, one new and one old. Following confirmation of T. palmi in the "new glasshouse", the inspector subsequently visited and took samples from the "old glasshouse". T. palmi was also confirmed on these premises, although at much lower population levels than in the new house. The pest was absent from some areas of the "old glasshouse", which was divided into large individual blocks.
3. Following the initial identification of T. palmi, a statutory notice was served to stop any movements of plants or produce from the site. This was subsequently modified to allow cut chrysanthemums to be moved direct to supermarkets, subject to a treatment and visual inspection for T. palmi prior to marketing.
4. The outbreak was notified to the European Commission in a letter dated 10 May 2000 and was formally declared to be eradicated on 17 July 2001, using a definition agreed by the Eradication Campaign Review Group.
Inspection and Investigation
5. Frequent inspection visits were made to the site, 60 to the "new house" and 56 to the "old house", to monitor and send traps for diagnosis, and to discuss control and eradication strategies. In total, a period of time equivalent to eight weeks was spent by inspectors at the site. Significant additional time was spent in meetings, in diagnosis and policy discussion. The total cost of this work is being assessed. Moreover, all neighbouring glasshouses were visited and traps installed, in order to assess whether this was an isolated outbreak or had spread. Nurseries within 1 km (16 premises) were visited four times; those between 1-3 km (30 premises) were visited twice; and those between 3-5 km (64 premises) were visited once.
6. Investigations into the origin of the outbreak proved difficult. Part of the new site house was used as a packhouse for packing cut flowers and houseplants, mainly sourced from and through The Netherlands, while the chrysanthemum cuttings were of Kenyan origin. T. palmi had not been recently reported in the The Netherlands, and had never been found in Kenya, so neither of these origins could be shown to be the cause of the outbreak. Other similar nurseries throughout the UK which received Kenyan chrysanthemum cuttings were inspected, but no other outbreaks of T. palmi were found then, or since. The company did not buy in orchids direct from Thailand or other far-eastern countries. Anecdotal reports from staff at the site suggested that the pest had been present for some months before the confirmation in April 2000, making any link to a specific consignment impossible to establish. The source of the outbreak remains unknown and no other outbreaks are known in the UK.
7. In line with International Standard for Phytosanitary Measures no. 9, ‘Guidelines for Pest Eradication Programmes’, an Eradication Campaign Review Group was formed and met for the first time in September 2000. This group, chaired by a Principal PHSI and consisting of representatives from the three parts of the Plant Health Service – inspectorate, laboratory and policy - met regularly to monitor progress on of the eradication campaign and to discuss wider issues. The Group also decided what period of freedom from the pest would be necessary before eradication could be confirmed. Given the continuous nature of production in the glasshouses, there was no period in which plants would not be growing. As a result, a definition was agreed of one complete crop cycle of thirteen weeks. The site would remain under notice for two complete crop cycles before official restrictions were dropped. In addition a review date for the eradication campaign was set at 31st March 2001. If T. palmi were still being found at that date, a different approach to eradication would be adopted.
Course of the Outbreak
8. During the course of the outbreak, Dominic Collins of CSL monitored the numbers of T. palmi recorded on traps collected by the PHSI. Graphs showing the numbers in the two glasshouses are attached at Annex I. These show the outbreaks in both peaking in mid-September, at which stage the operators carried out an intensive programme of eradication (see below). This combined approach appears to have been very successful, and resulted in the beginning of the end of the outbreak.
Means of eradication
9. The eradication campaign was necessarily intensive and involved the use of a range of treatments. The crop was grown in rotation around the glasshouses and vacant beds in the areas of heaviest infestation awaiting new plants were fumigated using methyl bromide. Soil drenches and leaf treatments were also used, the latter’s proving more effective on young plants and on the wider spaced plants used for production during the winter months. The choice of spraying nozzle and adjuvant also proved critical to ensuring that leaf treatments penetrated the canopy. During the winter the soil of the crop was covered with plastic and the plants grew through this. Intensive trapping was also tried in some areas, partly to assess the efficacy of the treatments and partly to reduce numbers. In order to intensify the campaign, emergency plant health off-label approval was obtained to use imidacloprid as a soil treatment.
10. During the outbreak, different coloured sticky traps were used to ascertain which were most effective in attracting the T. palmi. They were most attracted by blue or white traps; yellow traps were less effective. To monitor the freedom from pests of flowers being packed for despatch, traps were set above the packing line, and Berlese funnels were used to check samples of flowers. At Annex II is a report from Andrew Gaunt, the PHSI who used this sampling method, which suggests that it is very slow and can only be used for a very limited sample.
Proof of eradication
11. In addition to continuous monitoring of traps, CSL set bait plants during June 2001 to attract any residual T. palmi population. Before placing in the glasshouse the plants were tested for freedom from Cucumber mosaic virus, Tomato spotted wilt virus, Impatiens necrotic spot virus, Tomato aspermy and Chrysanthemum virus B. The plants selected were 16 Solanum nigrum, eight Solanum S. melongena and six Vicia faba, all of which had been shown to be attractive to T. palmi. The plants were left in the glasshouse for fourteen days, and were then collected in sealed bags and returned to the laboratory, where they were inspected for the presence of T. palmi.
12. No thrips were detected on the plants. Coupled with results from the traps, this project provided additional evidence to show the eradication had been successful. Traps were also placed around the harvesting and packing machinery where they might pick up any disturbed thrips. Once again, no T. palmi were detected.
Discussion
13. Although the nursery is a major producer of chrysanthemums, the pest had little, if any, economic impact in terms of damage to plants and rejection of flowers. Despite the intensity of the outbreak, at one stage the only damage observed was small marks on the plant leaves. These did not affect the crop value. Clearly there were additional costs for the company because of the additional treatments it had to apply. These were estimated at approximately £100,000 (around €164,000), but these were partially mitigated by an increase in quality and demand for the crop.
14. During the outbreak there was concern amongst neighbouring growers about the risks of the pest spreading to their premises. At its height, when the population inside the new house peaked, a few T. palmi were detected on traps immediately outside the glasshouses. Continued monitoring did not, however, reveal any further findings, providing a strong indication that the pest had not established outside the glasshouses themselves. The PHSI kept the neighbouring growers informed through a number of meetings and was able to satisfy them that potential pathways for spread were being controlled. A poster and accompanying leaflet were given to all 64 nurseries within 5 km of the outbreak site and information about the outbreak, and pest appearance and biology were kept maintained on the Plant Health Service website.
Conclusions
15. The pest proved very difficult to control in the early stages and new techniques and treatments were required. Despite early fears, eradicatition proved possible, albeit at considerable cost to the company and the Plant Health Service. These costs were, however, much less than those which would have been involved in crop destruction and the associated loss of markets.
16. With subsequent changes in pesticide availability, some of the measures employed are now unavailable in the UK. A similar outbreak may therefore prove even more difficult to eradicate in future. Applications are being made to the pesticide registration authority to extend the approvals of some newly introduced active ingredients, but this will be take time consuming and may well not be successful and the outcome is uncertain.
17. The company involved is both very progressive and
influential throughout both the UK and European horticultural industry,
and eradication was a very important priority for them. They were exceptionally
helpful and invited technical assistance from varying sources.
Plant Health Division
Department for Environment,
Food and Rural Affairs
August 2001
Graph of population of T. palmi New House
Graph of population of T. palmi at Old House
Report on the use of Berlise funnels for finding Thrips palmi at a UK cut flower nursery
Introduction
During the outbreak of Thrips palmi in a glasshouse in West Sussex, there was a need to monitor the out-going crop from the site. Several methods were used, including manually knocking out thrips from the cut bunch and putting up sticky traps around the harvesting machinery. These methods were supplemented by use of two Berlese funnels to check the flower bunches leaving the site.
Use of the Berlese funnels
The two funnels were set up in the new glasshouse as there was a higher concentration of pest on this site compared to the old house. The funnels were used very early on in the outbreak to monitor the out-going crop and to collect samples for resistance testing. They were also used later in the outbreak, again to check the out-going crop.
A plant at the early bud phase, the crop stage in which most thrips had been seen, was cut at the base using secateurs. As thrips could be found all over the infested plants, the whole plant was cut into small sections directly into the funnel. The funnels were then left for half an hour to collect any thrips which were present.
Findings
In the early stages, when the crop had high levels of thrips, some could be found using the funnel, but not many. For the collection of thrips for resistance testing, the bulk of the samples were taken from nightshade weeds in the crop, which the thrips had found very attractive.
Once levels of thrips had started to fall after August, none was thrips were found at all using the funnels. During a month of inspections, about 48 flowers were checked using the funnels and no thrips were found. During inspections in 2001, about 200 stems were checked out of 900,000 which left the site during this time and nothing was found. This was consistent with the other methods of checking: neither manual nor sticky trap checks found any thrips.
Conclusions
It appears that because the greenhouse is warm all the time, the thrips are active all the time. During harvesting, therefore, thrips are active over the surface of the flowers and appear to drop off in the processing. Harvesting is quite a rough process of pulling the crop out, bunching the flowers together and putting them on a conveyor belt to the machine which ties the bunch. All these stages knock the crop about. When funnels are used at the airports to check imported flowers, the technique is more successful because the thrips have either just hatched and emerged or have hidden in deep crevices in certain crops like karellas (Momordica sp.) and so are attracted into the funnels.
The funnels were slow and could only check a small fraction of the crop going out. As a result of this experience, use of the funnels ceased and other methods of detection were used.
Plant Health and Seeds Inspectorate
Chichester
14 May 2001
Page last modified:
10 Oct 2006
Page published: 3 May 2003