Project title: Baby-leaf Cruciferae and Watercress: Improved control of Scaptomyza flava. Project number: FV 408. Project leader: Jude Bennison

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1 Project title: Baby-leaf Cruciferae and Watercress: Improved control of Scaptomyza flava Project number: FV 408 Project leader: Jude Bennison Report: Final report, March 2013 Previous report: - Key staff: Location of project: Tom Pope* Gemma Hough Kerry Maulden Jonny Kerley Rob Drummond ADAS Boxworth and commercial farms Industry Representative: Will Archer Date project commenced: 1 May 2012 Date project completed (or expected completion date): 31 March 2013 *Project Leader until leaving ADAS August 2012 Agriculture and Horticulture Development Board All rights reserved

2 DISCLAIMER AHDB, operating through its HDC division seeks to ensure that the information contained within this document is accurate at the time of printing. No warranty is given in respect thereof and, to the maximum extent permitted by law the Agriculture and Horticulture Development Board accepts no liability for loss, damage or injury howsoever caused (including that caused by negligence) or suffered directly or indirectly in relation to information and opinions contained in or omitted from this document. Copyright, Agriculture and Horticulture Development Board All rights reserved. No part of this publication may be reproduced in any material form (including by photocopy or storage in any medium by electronic means) or any copy or adaptation stored, published or distributed (by physical, electronic or other means) without the prior permission in writing of the Agriculture and Horticulture Development Board, other than by reproduction in an unmodified form for the sole purpose of use as an information resource when the Agriculture and Horticulture Development Board or HDC is clearly acknowledged as the source, or in accordance with the provisions of the Copyright, Designs and Patents Act All rights reserved. AHDB (logo) is a registered trademark of the Agriculture and Horticulture Development Board. HDC is a registered trademark of the Agriculture and Horticulture Development Board, for use by its HDC division. All other trademarks, logos and brand names contained in this publication are the trademarks of their respective holders. No rights are granted without the prior written permission of the relevant owners. The results and conclusions in this report are based on an investigation conducted over a one-year period. The conditions under which the experiments were carried out and the results have been reported in detail and with 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 interpretation of the results, especially if they are used as the basis for commercial product recommendations. Agriculture and Horticulture Development Board All rights reserved

3 AUTHENTICATION We declare that this work was done under our supervision according to the procedures described herein and that the report represents a true and accurate record of the results obtained. Jude Bennison Senior Research Entomologist ADAS Signature... Date... Report authorised by: Dr. Tim O Neill Horticultural Research Manager ADAS Signature... Date... Agriculture and Horticulture Development Board All rights reserved

4 CONTENTS GROWER SUMMARY... 1 Headlines... 1 Background... 1 Summary of the project and main conclusions... 2 Financial Benefits... 5 Action Points... 6 SCIENCE SECTION... 7 Introduction... 7 Objective 1: Relate trap catches of S. flava adults to crop damage in a baby-leaf cruciferous crop and a watercress crop... 8 Materials and methods... 8 Results and Discussion... 9 Objective 2: Investigate the efficacy of pesticide spray applications to reduce leaf puncture damage caused by S. flava in baby-leaf cruciferous crops Materials and methods Results and Discussion Objective 3: Record survival of S. flava larvae developing within pesticide treated leaves of baby-leaf Cruciferae in the field and under controlled laboratory conditions. In addition, the presence of hymenopteran parasitoids and the proportion of parasitized leaf miner larvae will also be recorded Objective 4: Record survival of S. flava adults when exposed to baby-leaf cruciferae plants treated with pesticide spray applications under controlled laboratory conditions Materials and methods Results and Discussion Conclusions Knowledge and Technology Transfer References Agriculture and Horticulture Development Board All rights reserved

5 GROWER SUMMARY Headlines In a rocket field trial no products were effective at reducing leaf puncturing by Scaptomyza flava which could have been due to further S. flava adults migrating into the experimental plots following treatment. In laboratory tests on detached rocket leaves two experimental products and Tracer gave effective (78-100%) kill of S. flava after 48 hours Background During summer 2009, leaf miners caused serious economic damage on watercress and Cruciferae grown as baby-leaf salads in central, eastern and southern England. As a result, growers incurred economic losses resulting from increased use of pesticide application, crop rejection and additional packhouse labour inputs. Prior to this little damage by leaf miners had been observed and they were not considered as a significant pest. Research work completed in March 2011 (HDC project FV 376), confirmed that Scaptomyza flava (Figure 1a) was the leaf miner responsible for the damage. The large oval leaf punctures are made by adult females using their robust, saw-toothed ovipositors (egg-laying tubes, Figure 1b and c) while the larvae hatch from the eggs and feed between the upper and lower leaf surfaces, causing broad blotch mines (Figure 1d). a) b) Agriculture and Horticulture Development Board All rights reserved 1

6 c) d) Figure 1. a) S. flava adult b) saw-toothed ovipositor (egg-laying tube) of adult female which is used to make leaf punctures c) oval leaf punctures d) blotch mine made by larvae in a rocket leaf. A field trial was conducted in 2010 (HDC project FV 376) to test the efficacy of eight pesticides, only the organophosphorus pesticide dimethoate (not approved for use on babyleaf salads) was effective in reducing leaf puncturing. Laboratory tests with adult flies indicated the development of resistance to pyrethroid pesticides (Hallmark (lambdacyhalothrin) was used in the tests, which has an EAMU for use on outdoor rocket and babyleaf brassicas). This potential resistance may explain the increased status of S. flava as a key pest. The most effective method for reducing leaf puncturing currently is the use of crop covers to prevent access of adult flies, but these are expensive and can alter the environmental conditions (Personal communication, Will Archer). This project (FV 408) aimed to reduce damage associated with S. flava on baby-leaf Cruciferae and watercress. Summary of the project and main conclusions Objective 1: Relate trap catches of S. flava adults to crop damage in a baby-leaf cruciferous crop and a watercress crop. This study was done on a rocket crop in Norfolk and a watercress crop in Dorset. White sticky traps were positioned at crop height and replaced each week by the grower between late April and September From mid-june to early July when the numbers of adult flies first peaked, 60 plants at each site were assessed for leaf puncturing over a 3-week period. Numbers of flies per trap were much lower in 2012 than when monitored in the previous project in In mid-late June, mean numbers of Scaptomyza species per trap were 234 and 78 in the rocket and Agriculture and Horticulture Development Board All rights reserved 2

7 Mean % rocket leaves with punctures watercress crops respectively, compared with over 3,000 S. flava per trap in a rocket crop in No clear relationships were observed at either site between the numbers of Scaptomyza caught on the traps and the amount of puncturing damage. It was concluded that more intensive monitoring using a greater number of traps over several seasons would be needed in order to develop the use of traps as a monitoring or prediction tool to aid Scaptomyza management strategies. Objective 2: Investigate the efficacy of pesticide spray applications to reduce leaf puncture damage caused by S. flava in baby-leaf cruciferous crops. The efficacy of 11 pesticides in reducing leaf puncturing damage was tested on a rocket crop in Norfolk. Two and seven days after treatment, 10 plants were removed from each plot and the amount of puncturing damage was recorded. When compared to the untreated control, none of the pesticide treatments significantly reduced the mean percentage of leaves with punctures (Figure 2). On day 2, only slight Scaptomyza activity was observed but by day 7 over 40% leaves had more than a mean of three punctures per leaf. Further Scaptomyza flies migrating into the small trial plots after treatment could have diluted any significant reduction in numbers of flies achieved by the treatment Day 2 Day Untreated Agrimec Gazelle HDCI 045 HDCI 046 HDCI 047 Decis Savona Hallmark Pyrethrum Movento Tracer Treatment Figure 2. Mean % rocket leaves (n=10 plants) with punctures 2 and 7 days after treatment Agriculture and Horticulture Development Board All rights reserved 3

8 Objective 3: Record survival of S. flava larvae developing within pesticide-treated leaves of baby-leaf Cruciferae in the field and under controlled laboratory conditions. The presence of any parasitoids and the proportion of parasitized leaf miner larvae will also be recorded. Mined rocket leaves were collected from untreated plants around the field trial plots at the Norfolk site, in order to set up a glasshouse culture of S. flava for the laboratory tests. However, after the larvae in the mines had pupated, instead of adult S. flava emerging from the pupae, parasitic wasps emerged. These were confirmed by the Natural History Museum as the naturally occurring parasitoids, Dacnusa temula (Figure 3) and Chrysocharis pallipes. Mined pak choi leaves collected from another field site in autumn 2012 were used to set up the glasshouse culture of S. flava at ADAS Boxworth. Due to the limited number of S. flava in the culture laboratory tests were conducted on adult flies (see Objective 4) rather than on larvae, as adults cause the initial damage that can cause crop rejection. Figure 3. Dacnusa temula emerged from Scaptomyza pupae Ben Emmett Objective 4: Record survival of S. flava adults when exposed to baby-leaf Cruciferae plants treated with pesticide spray applications under controlled laboratory conditions. Although none of the pesticides used in the field trial significantly reduced leaf puncturing damage, HDCI 045, HDCI 047 and Tracer (spinosad) were selected for further laboratory testing after consultation with growers and the HDC. A detached rocket leaf was dipped into the pesticide (used at the same rate as in the field trial) and allowed to dry before being added to a Petri dish (five replicate dishes per treatment). Two S. flava adults from the glasshouse culture were then added per dish along with a piece of cotton wool soaked in a honey and water solution as a food source to prevent the flies dying from starvation. Numbers of live and dead flies were assessed after 24 and 48 hours. After 24 hours, Tracer and HDCI 047 had significantly reduced the percentage of surviving S. flava adults compared with the untreated and HDCI 045 treatments. Tracer resulted in Agriculture and Horticulture Development Board All rights reserved 4

9 Mean % of surviving Scaptomyza flava adults after 48 hours 100% kill within 24 hours. After 48 hours all three pesticide treatments led to significantly more dead flies than on untreated leaves (Figure 4), with HDCI 045 and HDCI 047 killing a mean of 78% and 89% flies respectively, compared with the 10% natural mortality in the untreated controls. These results demonstrated the residual activity of the three pesticide treatments against adult flies under controlled conditions. Further laboratory studies are needed to determine the residual persistence of effective pesticides against adult S. flava. No leaf punctures were observed during the tests. The effect of the pesticides on leaf puncturing needs to be assessed on whole plants under controlled conditions, as the adult females probably reject detached leaves for egg laying a b b b Untreated HDCI 045 HDCI 047 Tracer Treatment Figure 4. Mean % of surviving S. flava adults after 48 hours. Treatments with different lower case letters above the bars (a, b) are significantly different from each other. Treatments with the same lower case letters above the bars performed equally. Financial Benefits Only very low levels of leaf miner puncturing in salad Cruciferae are tolerated by retailers which can potentially result in total crop write-off for major producers. For example, an average yield is 7,000 kg/ha and the cost to buy replacement material is approximately 2.40/kg (therefore 2,400/tonne). Therefore, replacing a 20 tonne weekly programme during the summer would result in a grower cost of 48,000. However, the loss of revenue would be far greater if a producer did not supply to a retailer. Use of crop covers effectively prevents access by adult flies but currently there is no effective pesticide for preventing leaf damage when covers are removed a few days before harvest, or on farms where covers are not used. An effective additional method for reducing damage by S. flava in baby-leaf Cruciferous crops and watercress therefore has considerable financial benefits for growers at times of high pest pressure. Agriculture and Horticulture Development Board All rights reserved 5

10 Action Points Do not rely on pesticides for control of S. flava and avoid using pyrethroid pesticides as resistance is likely. Avoid growing baby-leaf brassicas or watercress near to oilseed rape which is another host crop for the pest. Where practical, use insect-proof netting to cover crops in order to prevent access by adult flies, particularly during periods of high pest pressure. White sticky traps can be used for monitoring when Scaptomyza adult numbers increase but so far there is no clear correlation between adult numbers and leaf puncturing damage. Agriculture and Horticulture Development Board All rights reserved 6

11 SCIENCE SECTION Introduction In recent years (2009 onwards), a leaf miner pest has caused significant damage to babyleaf cruciferous crops (e.g. rocket, tatsoi, mizuna) and watercress in central and southern England. Prior to this, leaf miner was not considered an important pest on these crops. Research in HDC project FV 376, completed in March 2011, confirmed that Scaptomyza flava was responsible for this damage. Research using leaf dip and glass tube tests in this project indicated the development of resistance to pyrethroid pesticides (Hallmark (lambdacyhalothrin), which has an EAMU for use on outdoor rocket and baby-leaf brassicas). Pyrethroid pesticides are used on these crops for control of other pests and this likely resistance in S. flava may explain its recent increased status as a key pest. For growers of baby-leaf salad crops, preventing leaf puncturing by adult S. flava is a priority as this damage can lead to crop rejection. The leaf punctures are made by the adult female fly which uses her robust, saw-toothed ovipositor (egg laying tube) to make large oval punctures which are used for feeding and some are also used to lay eggs into the leaf. Following this, the larvae hatching from the eggs feed between the upper and lower leaf surfaces, causing broad blotch mines. During the summer of 2009, growers incurred significant economic losses resulting from increased use of pesticide application, crop rejection and additional packhouse labour inputs. In a field trial testing the efficacy of eight pesticides against S. flava on rocket, only the organophosphorus pesticide dimethoate (not approved for use on baby-leaf salads) was effective in reducing leaf puncturing (HDC project FV 376). Currently, the most effective method of controlling S. flava damage is through the use of crop covers to prevent access by adult flies, however these are expensive and they can increase the incidence of diseases such as downy-mildew (Personal Communication, Will Archer). Initial research in 2012 monitoring S. flava adults using white sticky traps showed that adults were active between April and September, with several (probably three or four) generations during the summer months (HDC project FV 376). Populations seemed to fluctuate between sites, but trapping data indicated that sudden, unpredictable and large increases can occur at different times on different sites. It is not known how these peaks in pest numbers relate to crop damage. Agriculture and Horticulture Development Board All rights reserved 7

12 This project (FV 408) aimed to reduce damage associated with Scaptomyza flava on babyleaf Cruciferae and watercress. Specific objectives were: 1. Relate trap catches of S. flava adults to crop damage in a baby-leaf cruciferous crop and a watercress crop. 2. Investigate the efficacy of pesticide spray applications, to reduce leaf puncture damage caused by S. flava in baby-leaf cruciferous crops. 3. Record survival of S. flava larvae developing within pesticide treated leaves of babyleaf Cruciferae in the field and under controlled laboratory conditions. In addition, the presence of hymenopteran parasitoids and the proportion of parasitized leaf miner larvae will also be recorded. 4. Record survival of S. flava adults when exposed to baby-leaf Cruciferae plants treated with pesticide spray applications under controlled laboratory conditions. Objective 1: Relate trap catches of S. flava adults to crop damage in a baby-leaf cruciferous crop and a watercress crop This study aimed to relate trap catches of S. flava adults to crop damage in a wild rocket crop for baby-leaf salad production in Norfolk and a watercress crop in Dorset. Materials and methods Suitable crop sites were selected with the growers that would have crops present throughout most of the growing season (April to August). White sticky traps were attached to a piece of plywood board (25x35cm) on a short length stake which was hammered into the ground. Traps were positioned at crop height and the grower was shown how to replace the traps which were sent to ADAS Boxworth each week between late April and September On receiving the traps the number of S. flava adult per trap were recorded. From mid-june to early July when the numbers of adult flies first started to peak, damage assessments of the crops close to the trap were conducted. Three small areas in each crop (1.6m x 5m) were marked out with canes on 14 June 2012 at the Norfolk site and 21 June 2012 at the Dorset site (Figure 1). Agriculture and Horticulture Development Board All rights reserved 8

13 Figure 1. Watercress monitoring site in Dorset. Assessments Within these three designated areas, 20 plants were tagged (Figure 2b). At the watercress site, the number of puncture holes (Figure 2a) and leaf mines were recorded on the selected plants on 21 June (the day they were tagged) and on three further occasions on 29 June, 5 and 13 July. At the rocket site three assessments took place on 21, 27 June and 6 July. On each assessment date extensive damage by flea beetle was observed on the rocket. a) b) Figure 2. a) S. flava puncturing damage on watercress at the Dorset trial site. b) Tagged wild rocket at the Norfolk site Results and Discussion Scaptomyza species were identified on the traps and these species were confirmed by the Natural History Museum. No clear relationships were observed between the numbers of Scatomyza species recorded on the traps and the amount of puncturing damage in either monitoring site. Agriculture and Horticulture Development Board All rights reserved 9

14 Prior to the damage assessment in mid-june at both sites, adult numbers had increased to 234 and 78 per trap at the rocket and watercress sites, respectively (Figures 3 and 4). No puncturing damage was observed on the first assessment. Over the following three weeks, numbers of adults per trap decreased at the rocket site and remained relatively constant at the watercress site, and mean leaf punctures per leaf reached 0.9 and 0.8 on the rocket and watercress, respectively. Numbers of flies per trap were much lower in 2012 than when monitored in 2010 in the previous project (FV 376), when numbers reached over 3,000 S. flava per trap in a rocket crop. Figure 3. Scaptomyza adults per trap and mean numbers of punctures per leaf on rocket crop in Norfolk Figure 4. Scaptomyza adults per trap and mean number of punctures per leaf on watercress crop in Dorset. Agriculture and Horticulture Development Board All rights reserved 10

15 Monitoring is a valuable tool which can be used to determine the main periods of activity of a pest over the growing season. This can sometimes be used to help time the application of control measures for greater effectiveness. In this study it was not possible to relate trap catches of S. flava adults to crop damage, as no clear relationship was observed between the number of adults per trap and the amount of leaf puncturing damage on the crop. It was concluded that to develop the use of traps as a monitoring tool to aid management strategies, more intensive monitoring would be required with a greater number of traps over several seasons. Objective 2: Investigate the efficacy of pesticide spray applications to reduce leaf puncture damage caused by S. flava in baby-leaf cruciferous crops Materials and methods Treatments The experiment assessed the efficacy of 11 pesticide sprays in reducing leaf puncturing damage compared with an untreated control (Table 1). Each treatment had four replicate plots (48 plots in total). Each plot measured 1.6m x 5m arranged in a fully randomised block design. Agriculture and Horticulture Development Board All rights reserved 11

16 Table 1. Pesticide treatments in 2012 field trial (EAMU is Extension of Authorisation for minor use (formerly known as SOLAs, Specific Off-label Approvals)) Treatment. Product Active ingredient Approval status on outdoor rocket/baby leaf brassicas 1 Untreated Agrimec abamectin Not approved (approved on certain other crops) 3 Gazelle acetamiprid EAMU 4 HDCI HDCI HDCI Decis Protech deltamethrin Not approved in UK Not approved (approved on certain other crops) Not approved in UK EAMU 8 Savona fatty acids EAMU 9 Hallmark 10 Pyrethrum 5 EC lambdacyhalothrin pyrethrum EAMU Label 11 Movento spirotetramat EAMU 12 Tracer spinosad EAMU Rate 0.48 l product in 300 l water/ha 250 g product in 300 l water/ha 0.3 l product in 300 l water/ha 175 ml product in 300 l water/ha 1.5 kg product in 300 l water/ha 500 ml product in 300 l water/ha 6 litres in 300 l water/ha 75 ml in 300 l water/ha 20 ml in 275 l water/ha (i.e. 20 ml in 5 l of water & <1.1l product/ha) 0.5 l product in 300 l water/ha 240 ml product in 300 l water/ha Trial site The experiment was carried out on a wild rocket crop at a site in Norfolk. Crop covers (Enviromesh) were used to protect the crop from pests but the trial plots were uncovered during the trial period. The trial was carried out in July when numbers of adult Scaptomyza had started to increase on white sticky traps used in Objective 1. Assessments made before pesticide application On 4 July 2012 the trial plots were uncovered and an initial assessment was carried out to confirm that no leaf puncturing was present prior to application of the trial pesticides. Ten Agriculture and Horticulture Development Board All rights reserved 12

17 plants were randomly selected from each plot from within the centre 3-metre bed away from the edge. At each assessment date, the numbers of leaves on each plant were recorded together with the number of puncture holes (Figure 5). Other pest damage was also recorded (e.g. flea beetle feeding damage). No damage was observed on the initial assessment. Figure 5. Puncturing damage on rocket caused by Scaptomyza adults. Pesticide application On the same day the crops were uncovered, pesticide treatments were applied by ADAS (Figure 6). Figure 6. Pesticide application to rocket in field trial in Norfolk Assessments made after pesticide application On 6 July and 11 July 2012 (days 2 and 7 after treatment, respectively), 10 plants from each plot were collected as described for the pre-application assessments and brought back to ADAS Boxworth for assessment. In addition to pest damage, any phytotoxic effects Agriculture and Horticulture Development Board All rights reserved 13

18 of treatments were also recorded (spotting, chlorosis, scorching or poor plant growth). All plants treated with non-approved pesticides (treatment 2, 4, 5 and 6) were manually removed from the plots and disposed of and the remaining crop was disposed of by the grower. Statistical analysis Data on the mean number of punctures per leaf, mean number of punctures per plant and mean percentage of leaves with punctures on day 2 and 7 after treatment were analysed using analysis of variance (ANOVA) in GenStat (12 th Edition). Analysis determined whether there was a significant overall effect of treatment, individual comparisons between treatment means were completed using least significant difference (LSD) (P<0.05). Results and Discussion Phytotoxic effects of pesticides No phytotoxic effects of treatment with any of the pesticides were observed. Efficacy of pesticides When compared with the untreated controls, there was no significant effect of any of the 11 pesticides on the mean number of punctures per plant (Figure 7), punctures/leaf (Figure 8) or the mean percentage leaves with punctures (Figure 9). Punctures per plant: On day 2, low Scaptomyza activity was observed, but by day 7 considerably more punctures per plant were recorded, with a 27-fold increase in the number of punctures per plant in untreated controls (mean of 40 punctures per plant) (Figure 7). Agriculture and Horticulture Development Board All rights reserved 14

19 Mean no. of punctures/leaf Mean no. of punctures/plant Day 2 Day Untreated Agrimec Gazelle HDCI 045 HDCI 046 HDCI 047 Decis Savona Hallmark Pyrethrum Movento Tracer Treatment Figure 7. Mean number of punctures per plant 2 and 7 days after treatment. Punctures per leaf: By seven days after treatment, there was a mean of five punctures per leaf in untreated control plot and none of the treatments gave a significant reduction (Figure 8). This amount of damage would be unacceptable in the harvested crop Day 2 Day 7 0 Untreated Agrimec Gazelle HDCI 045 HDCI 046 HDCI 047 Decis Savona Hallmark Pyrethrum Movento Tracer Treatment Figure 8. Mean number of punctures per leaf 2 and 7 days after treatment Percentage of leaves with punctures: Seven days after treatment, a mean of 62% of the leaves were punctured in untreated control plots and none of the treatments gave a Agriculture and Horticulture Development Board All rights reserved 15

20 Mean % leaves with punctures significant reduction (Figure 9). This amount of puncturing damage would cause the crop to be unmarketable at harvest Day 2 Day Untreated Agrimec Gazelle HDCI 045 HDCI 046 HDCI 047 Decis Savona Hallmark Pyrethrum Movento Tracer Treatment Figure 9. Mean % leaves with punctures 2 and 7 days after treatment This field trial gave no evidence that any of the pesticides reduced puncturing damage by S. flava. However, this could be the result of further adult flies migrating into the trial plots following treatment, which could have diluted any significant reduction in numbers of flies achieved by the treatment. Future trials with larger experimental plots might help to reduce this effect. Growers have reported variable observed results in reduction in leaf puncturing damage by Scaptomyza in baby-leaf salad crops following insecticide treatment. At a SPGA meeting in October 2012, most reported that pyrethroid insecticides are now failing to give any noticeable control, although some growers reported some apparent reduction in leaf puncturing after use of spinosad (Tracer). Spinosad has an EAMU for use on outdoor rocket and baby-leaf brassicas. A study in New Zealand has reported that abamectin (e.g. Agrimec, Dynamec, not approved on outdoor rocket and baby-leaf brassicas in the UK) was effective against S. flava larvae and reduced the number of leaf mines (Martin et al. 2006). Depending on the amount of adult leaf puncturing damage, by the time leaf mines have developed on the crop, it is likely that the crop might already be unmarketable due to puncturing damage. Agriculture and Horticulture Development Board All rights reserved 16

21 Objective 3: Record survival of S. flava larvae developing within pesticide treated leaves of baby-leaf Cruciferae in the field and under controlled laboratory conditions. In addition, the presence of hymenopteran parasitoids and the proportion of parasitized leaf miner larvae will also be recorded Laboratory tests Mined pak choi leaves collected from another field site in autumn 2012 were used to set up the glasshouse culture of S. flava at ADAS Boxworth. Due to the limited number of S. flava in the culture, it was agreed with the HDC and industry representative to do the laboratory tests on adult flies (see Objective 4) rather than on larvae, as adults cause the initial damage that can cause crop rejection. Natural parasitoids Mined rocket leaves were collected from untreated plants around the field trial plots at the Norfolk site, in order to set up a glasshouse culture of S. flava for the laboratory tests. However, after the larvae in the mines had pupated, instead of adult S. flava emerging from the pupae, parasitic wasps emerged. These were confirmed by the Natural History Museum as the naturally occurring parasitoids, Dacnusa temula and Chrysocharis pallipes (Figure 10). These parasitoids are thought to be commonly occurring in the UK, indeed D. temula had been recorded as naturally parasitising S. flava on baby-leaf salad crops in previous years, by Ben Emmett, a retired Entomologist now working as a consultant to Vitacress (B. Emmett, personal communication). Figure 10. Dacnusa temula parasitoids emerged from Scaptomyza pupae Ben Emmett It is not known how much these naturally-occurring parasitoids could suppress S. flava populations. As they parasitise larvae, they occur too late to prevent crop damage. However, they could potentially form an important role in an Integrated Pest Management (IPM) strategy to control the pest, leading to reduction in S. flava populations over successive generations. It would be interesting to know how widespread these natural Agriculture and Horticulture Development Board All rights reserved 17

22 parasitoids are in baby-leaf salad and other host crops. Furthermore, determining whether these parasitoids can survive any effective pesticide applications for S. flava would also be of importance, as this would determine whether these pesticides would be compatible within an IPM programme. In New Zealand, research has suggested that while the larvae of S. flava are killed by abamectin, the parasitoid Asobara persimilis, was still able to continue its development (Martin & MacDonald, 2009). Objective 4: Record survival of S. flava adults when exposed to babyleaf cruciferae plants treated with pesticide spray applications under controlled laboratory conditions Materials and methods Source of S. flava A glasshouse culture of S. flava was set up on wild rocket plants in insect-proof cages in order to provide adults for the laboratory tests. To start off the culture, adults were reared through from mined pak choi leaves collected from a commercial crop. The glasshouse compartment temperature was set at approximately 20ºC. Treatments Although none of the pesticides tested in the field trial significantly reduced puncturing damage, after consultation with HDC, the industry representative and other baby-leaf salad growers and consultants, HDCI 045, HDCI 047 and spinosad (Tracer) were selected for further laboratory bioassays (Table 2). The experiment was done in February 2013, when sufficient adult S. flava were available in the glasshouse culture. For each treatment (except the untreated controls), a single detached rocket leaf was dipped into the pesticide (used at the same rate as in the field trial) and allowed to dry before being added to a Petri dish with insect-screened ventilated lids (five replicate dishes per treatment). Two S. flava adults were then collected from the culture and added to each dish using an aspirator ( pooter ). A piece of cotton wool soaked in a honey and water solution was also added to the dish as a food source, to prevent the flies dying from starvation. Dishes were arranged in a randomised design (Figure 11) and kept in an incubator at 20 C 16L: 8D. Agriculture and Horticulture Development Board All rights reserved 18

23 Figure 11. Laboratory pesticide test Assessment The numbers of live and dead flies were assessed after 24 and 48 hours. Statistical analysis An ANOVA was performed on the percentage of surviving flies recorded after 24 hours and 48 hours in GenStat (12th Edition). If there was an significant overall effect of treatment, individual comparisons between treatment means were completed using least significant difference (LSD) (P<0.05). Table 2. Pesticide treatments used in lab bioassays (EAMU is Extension of Authorisation for Minor Use (formerly known as SOLAs, Specific Off-label Approvals)) Product Active ingredient Approval status on Rate outdoor rocket/baby leaf brassicas Untreated HDCI Not approved in UK 0.3 l product in 300 l water/ha HDCI Not approved in UK 1.5 kg product in 300 l water/ha Tracer spinosad EAMU 240 ml product in 300 l water/ha Results and Discussion After 24 hours HDCI 047 and Tracer had significantly reduced the percentage of surviving S. flava adults compared with the untreated and HDCI 045 treatment (Figure 12a). Tracer resulted in 100% kill within 24 hours (Figure 13). After 48 hours all three pesticide treatments led to significantly more dead flies than on untreated leaves, with HDCI 045 and Agriculture and Horticulture Development Board All rights reserved 19

24 Mean % of surviving Scaptomyza flava adults after 48 hours Mean % of surviving Scaptomyza flava adults after 24 hours HDCI 047 killing a mean of 78% and 89% flies respectively, compared with the 10% natural mortality in the untreated controls (Figure 12b) a a b b Untreated HDCI 045 HDCI 047 Tracer a) Treatment a b b b Untreated HDCI 045 HDCI 047 Tracer b) Treatment Figure 12. Mean % of surviving S. flava adults after a) 24 hours and b) 48 hours. Treatments with different lowercase letters above the bars (a, b) are significantly different from each other. Treatments with the same lower case letters above the bars performed equally. Agriculture and Horticulture Development Board All rights reserved 20

25 Figure 13. Dead S. flava adults in laboratory test These results confirmed the residual activity of the three pesticide treatments against adult flies under controlled conditions. No leaf punctures were observed during the tests. The effect of the pesticides on leaf puncturing needs to be assessed on whole plants under controlled conditions, as the adult females probably reject detached leaves for egg laying. None of the pesticides effectively reduced leaf puncturing in the field trial, indicating that the residual activity was insufficient to kill adult S. flava that flew into the trial plots following treatment. Further laboratory studies would be needed to determine the residual persistence of effective pesticides against adult S. flava. Any pesticides with sufficient residual activity against adult flies and that effectively reduce leaf puncturing would then need to be tested in large plots in a further field trial. Ideally, pesticides with different modes of action should be identified with efficacy against S. flava, as relying on one (e.g. spinosad) is likely to lead to further development of insecticide resistance. Conclusions There was no clear relationship between sticky trap catches of adult S. flava and the level of puncturing damage observed. More intensive monitoring using a greater number of traps over several seasons would be needed in order to develop the use of traps as a monitoring or prediction tool to aid Scaptomyza management strategies. In a field trial on rocket, no pesticides were effective at reducing leaf puncturing damage two or seven days after treatment which could have been due to further S. flava adults migrating into the experimental plots following treatment. In laboratory tests on detached rocket leaves, HDCI 045, HDCI 047 and Tracer demonstrated a residual activity over a 48-hour period, killing % of adults Agriculture and Horticulture Development Board All rights reserved 21

26 within 48 hours. Further laboratory tests would be needed to confirm the maximum effective residual time after pesticide application for kill of S. flava adults and associated reduction in leaf puncturing. These results would indicate any need for pesticide repeat application to protect the crop from further immigrating adults. The laboratory results would then need validating in large-scale plots in a further field trial before any recommendations could be given to growers. Knowledge and Technology Transfer Presentations Update on improved control of Scaptomyza flava on baby-leaf cruciferae and watercress. BLSA Conference 2012, Kingsgate Conference Centre, Peterborough, November 2012 Project update to the SPGA, Agrii, Alconbury, Huntingdon. 5 February Publications Article in HDC News, April References HDC (2011) Baby leaf cruciferae: leaf miner identification, biology and control. Final report project FV 376 Martin, N. & MacDonald, F. (2009) Evaluating the impact of pesticides on Scaptomyza flava and its parasitoid, Asobara persimilis. New Zealand Journal of Crop and Horticultural Science. 37: Martin, N. A., Workman, P. J. & Hedderley, D. (2006) Susceptibility of Scaptomyza flava (Diptera: Drosophilidae) to pesticide. New Zealand Plant Protection. 59: Acknowledgements Thanks to the host growers for their help and co-operation in hosting the trials and sending sticky traps to ADAS. Agriculture and Horticulture Development Board All rights reserved 22