10 month project. Andrew Jukes Andy Richardson Paul Miller. Matt Rawson. 31 March 2012

Transcription

1 FV399 Project title: Improving control of brassica whitefly (Aleyrodes proletella) Project number: FV 399 Project leader: Rosemary Collier, University of Warwick Report: Final Report, March 2012 Previous report: Key staff: Location of project: Industry Representative: 10 month project Andrew Jukes Andy Richardson Paul Miller Elsoms Seeds, Warwick Crop Centre, Allium & Brassica Agronomy Ltd, Silsoe Spray Applications Unit Matt Rawson Date project commenced: 01 June 2011 Date project completed (or expected completion date): 31 March Agriculture and Horticulture Development Board

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 Agriculture and Horticulture Development Board. All rights reserved

3 AUTHENTICATION I declare that this work was done under my supervision according to the procedures described herein and that the report represents a true and accurate record of the results obtained. Rosemary Collier Director Warwick Crop Centre University of Warwick Signature... Date... Report authorised by: Professor Brian Thomas Deputy Head of the School of Life Sciences University of Warwick Signature... Date Agriculture and Horticulture Development Board. All rights reserved

4 CONTENTS Grower Summary... 1 Headline... 1 Background... 1 Summary... 1 Financial Benefits... 6 Action Points... 6 Science Section... 7 Introduction Field Trials Potted plant tests Spray application tests Discussion Conclusions Knowledge and Technology Transfer Acknowledgements References Agriculture and Horticulture Development Board. All rights reserved

5 GROWER SUMMARY Headline Movento was the most effective insecticide product for whitefly control on Brassica crops. Boom-mounted nozzle configurations did not give adequate under-leaf coverage of sprays regardless of nozzle type, application volume or forward speed. Dropleg spraying systems improved coverage on the undersides of leaves on Brussels sprout, but not on kale. Background Whitefly (Aleyrodes proletella) is becoming increasingly difficult to control on kale and Brussels sprout in particular. It is not clear why this is the case, although outbreaks appear to be more severe in hot, dry years (2003, 2006 and 2010). There are a number of possible insecticide products to control whitefly and programmes could be built around these products. Additionally there are questions about the best ways to apply spray treatments to maximise control since kale and Brussels sprout crops are particularly difficult targets for spray applications. Finally, some populations of whiteflies are resistant to pyrethroids. In this situation pyrethroid applications may exacerbate the whitefly problem by killing some of their natural enemies. Summary of the results and main conclusions The aim of the project was to evaluate insecticide spray programmes and application strategies that might improve control of Brassica whitefly. This was addressed through 1) field trials, 2) pot trials and 3) spray application tests in a wind tunnel. Four organisations collaborated to undertake this programme of work: University of Warwick (Warwick Crop Centre), Allium & Brassica Agronomy Ltd, Silsoe Spray Applications Unit (TAG) and Elsoms Seeds. Field trials on Brussels sprout and kale to evaluate spray programmes The aim of two field trials (Brussels sprout and kale) at Elsoms Seeds trials ground in Spalding was to evaluate a number of spray programmes using approved insecticides together with the application of a novel, coded insecticide product (HDCI 013) that had looked promising in earlier HDC-funded trials where incidental control of whitefly was recorded. Both trials were planted on 16 June The approved products were Movento (spirotetramat), Biscaya (thiacloprid) and Plenum (pymetrozine). The programmes used on 2012 Agriculture and Horticulture Development Board 1

6 Brussels sprout and kale differed because Biscaya is not approved on kale. Each treatment was replicated 4 times. The treatment programmes are summarised in Tables 1 and 2. Decis was evaluated alone (T2) and it was also included in one of the spray programmes to determine any secondary effects it might have on whitefly control through its impact on natural enemies if applied to control caterpillars (T3). Dipel DF (Bacillus thuringiensis) was included in a similar programme as a control (T4). All treatments were applied in 300 l water/ha using an AZO compressed air plot sprayer. Table 1. Treatments and application dates in the trial on Brussels sprout 12 Aug 25 Aug 9 Sep 22 Sep Code T1 Untreated Untreated Untreated Untreated Untreated T2 Decis Decis Decis Decis Decis T3 Movento + Decis Biscaya + Decis Movento + Decis Biscaya + Decis MBMB + Decis T4 Movento + Dipel DF Biscaya + Dipel DF Movento + Dipel DF Biscaya + Dipel DF. MBMB + Dipel T5 Plenum Movento Plenum Movento PMPM T6 Biscaya Plenum Biscaya Plenum BPBP T7 Movento Plenum + Movento Plenum + M(PB)M(PB) Biscaya Biscaya T8 Movento Movento Biscaya Biscaya MMBB T9 HDCI 013 Movento HDCI 013 Movento 13M13M T10 HDCI 013 HDCI Agriculture and Horticulture Development Board 2

7 Table 2. Treatments and application dates in the trial on Kale 12 Aug 25 Aug 9 Sep 22 Sep Code T1 Untreated Untreated Untreated Untreated Untreated T2 Decis Decis Decis Decis Decis T3 Movento + Plenum + Decis Plenum + Decis Decis Movento + Decis MPMP + Decis T4 Movento + Plenum + Dipel Movento +Dipel Plenum + Dipel Dipel DF DF DF DF MPMP + Dipel T5 Plenum Movento Plenum Movento PMPM T6 Movento Movento Plenum Plenum MMPP T7 HDCI 013 Movento HDCI 013 Movento 13M13M T8 HDCI 013 HDCI In both trials an assessment of whitefly numbers was made before treatments were applied and the plots were assessed following each treatment application. On Brussels sprout, there was a statistically significant effect of programme on the number of egg circles per plant from the second post-spraying assessment (7 September) onwards. In general, the most effective programmes started with Movento and included Biscaya. The Biscaya/Plenum programme (BPBP) was ineffective throughout. Programmes that reduced the number of egg circles also reduced the numbers of leaves with larvae. The four most effective programmes all started with Movento and included Biscaya and there was no difference between the three most effective programmes (MBMB + Decis, M(PB)M(PB), MBMB + Dipel), which had reduced the infestation to zero or close to zero by 4 October. Finally, programmes that reduced the number of egg circles and infested leaves also reduced adult numbers. The four most effective programmes all started with Movento and included Biscaya and there was no difference between the three most effective programmes (MBMB + Decis, M(PB)M(PB), MBMB + Dipel). As an example, Figure 1 shows the number of leaves with larvae per plant in the Brussels sprout trial. On kale, the most effective programmes for egg control included Movento and the two most effective programmes (MPMP + Decis, MPMP + Dipel) started with Movento and provided similar levels of control. Programmes MPMP + Dipel, MPMP + Decis and MMPP all reduced 2012 Agriculture and Horticulture Development Board 3

8 the number of infested leaves compared with the untreated control from 7 September onwards. MPMP + Dipel and MPMP + Decis were the two most effective programmes and were equally effective, reducing the infestation to almost zero on 4 October. These two programmes were also the most effective for control of adults. Decis alone did not reduce whitefly numbers compared with the insecticide-free control, it seems likely that the whitefly population at Elsoms trials ground is resistant to pyrethroid insecticides. In a number of instances the application of pyrethroid insecticides has also been shown to increase the numbers of unresponsive pests (e.g. pyrethroid resistant Myzus persicae), possibly because they kill natural enemies such as ladybirds and parasitic wasps. However, in these trials there was no evidence that the use of pyrethroids increased whitefly numbers. Whilst previous trials have indicated that the coded product HDCI 013 was effective against whitefly when applied as a module drench treatment, its performance as a foliar spray treatment was less convincing. 30 Mean number of leaves with larvae M(PB)M(PB) MBMB + Dipel MBMB + Decis MMBB 13M13M PMPM BPBP Untreated Decis 09-Aug 16-Aug 07-Sep 21-Sep 04-Oct Figure 1. Brussels sprout - number of leaves with larvae per plant (treatments ranked by level of control on 4 October). Potted plant tests Test plants infested with whitefly were treated with one of the two most effective insecticides identified in the field trial (Movento or Biscaya). Plants were sprayed using a hand sprayer and two types of treatment were applied to the outer leaves or to the crown of the plant. Sprays were applied over the top of the plants. Numbers of egg circles, larvae and adults were counted on a number of occasions thereafter. In the first test, numbers of larvae and 2012 Agriculture and Horticulture Development Board 4

9 adults increased on untreated control plants over the course of the trial. Both Movento treatments and the Biscaya-Crown treatment reduced larval numbers on all three assessment occasions compared with the untreated control. The Biscaya-Outer treatment reduced larval numbers on the first assessment occasion only (11 DAT). There was no treatment effect on adult numbers 20 days after spraying, but a statistically significant effect 33 days after spraying when numbers on all but the Biscaya-Outer treatment were reduced compared with the control. There was no statistically-significant effect of treatment on egg numbers. On untreated control plants in Test 2, numbers of larvae and adults decreased over the course of the test. There were no statistically-significant effects of treatment on any development stage. Examine spray deposition patterns with different application systems in the wind tunnel on the Silsoe site Whitefly colonies are typically found on the undersides of crop leaves and therefore pose a difficult target for the application of spray chemicals with a contact mode of action. This preliminary study aimed at using the controlled conditions in a wind tunnel to examine the extent to which the undersides of crop leaves could be targeted in the crops of Brussels sprout and kale using boom mounted application systems that could be easily configured on conventional machines. The work addressed the application variables relating to nozzle designs, application volumes, forward speeds and wind speeds during application. Deposition patterns were recorded by spraying a fluorescent tracer dye, illuminating treated leaves with an ultra-violet light and recording levels of coverage photographically. Sample leaves were taken from three levels up the plant, (top, middle and bottom) and at each level two leaves were taken from the front of the plant (i.e. facing the direction of sprayer travel) and from the side. Boom mounted nozzle configurations did not give adequate under-leaf coverage of sprays regardless of nozzle type, application volume or forward speed. Dropleg spraying systems were able to achieve good coverage on the undersides of leaves in Brussels sprout particularly in the centre of the canopy. It is likely that the use of droplegs together with overhead nozzles could achieve the levels of coverage needed for contact acting pesticides providing that the crop canopy is reasonably open and that total application volumes in excess of 300 L/ha are used. The kale plants and kale plant canopies were shown in this work to give conditions that made under-leaf deposits difficult to achieve and no effective approach was identified for achieving such deposits/coverage as part of this study Agriculture and Horticulture Development Board 5

10 Financial Benefits It is difficult to quantify crop losses due to whitefly, but this pest undoubtedly has an adverse effect on the quality and therefore marketability of kale and Brussels sprout buttons. Action points for growers Field trials and laboratory tests indicated that Movento is the most effective product for whitefly control approved currently. However, because the insecticide products were applied as part of programmes in the field trials it is difficult to determine their relative efficacy and persistence of activity. The results indicate that the most effective programmes began with Movento and that the most effective strategy was to separate the two Movento applications rather than apply them consecutively. It is possible that Movento treatments could be separated by a longer interval than used in these trials without reducing efficacy. There appeared to be little extra benefit of including Plenum in a programme based on Movento and Biscaya. A programme based on Biscaya and Plenum alone was ineffective. Whilst the results from this trial consistently indicate a pattern of treatment applications that was most effective, these trials were undertaken at the same time in a single location and the most effective pattern of applications might be different at another time of year, depending on development of the whitefly infestation. Pyrethroid insecticides are unlikely to control whitefly and should only be applied to crops if there is a specific susceptible target such as caterpillars. The potential adverse impact of pyrethroid insecticides on beneficial insects should be considered before using them as part of an IPM strategy. When using boom mounted nozzle systems, some small improvement in under-leaf coverage could be achieved by operating in high wind conditions. However, this improvement does not result in adequate deposits/coverage and there is a substantial drift risk that makes such an approach impractical. The use of spray adjuvants and changes to formulation properties would not facilitate under-leaf deposits and coverage with boom mounted nozzle systems. Further work should examine the use of electrostatically charged sprays delivered in an air stream as the only possible approach to achieving under-leaf deposition in canopies such as those with the kale crop Agriculture and Horticulture Development Board 6

11 SCIENCE SECTION Introduction Whitefly (Aleyrodes proletella) is becoming increasingly difficult to control on kale and Brussels sprout in particular. It is not clear why this is the case, although outbreaks appear to be more severe in hot, dry years (2003, 2006 and 2010). Research on the basic biology and ecology of cabbage whitefly was undertaken in the late 1930s (Butler, 1938a, b) and this provides very useful background information. More recently, there has been research on the overwintering status of cabbage whitefly (females overwinter in a state of ovarian diapause e.g. Adams (1985)) and on development times on, and preferences for, different cultivars of susceptible Brassica crops (e.g. Ellis et al.,1996; Iheagwam, 1978; Nebreda et al., 2005; Ramsey & Ellis, 1996; Trdan & Papler, 2002). Most recently, research in the UK has focused on insecticidal control (data obtained in other HDC projects targeted at control of aphids on Brassica crops) and a PhD student at the University of Greenwich (Simon Springate supervised by Dr John Colvin) has been undertaking work on the increasing importance of cabbage whitefly as a pest, and potential methods for its control. They tested populations of whitefly for resistance to certain insecticides and showed that certain whitefly populations are resistant to pyrethroid insecticides (Springate & Colvin, 2011). They also investigated the potential for native predators, in particular a species of ladybird and parasitic wasps (Encarsia spp.), to control whitefly. There are a number of possible insecticide treatments to control whitefly. In HDC trials focused on Brassica aphids some of these insecticides suppressed whitefly infestations and a novel insecticide also looked interesting. However, we do not really understand how to put together a spray programme to suppress whitefly. There are also questions about the best ways to apply spray treatments to maximise control. Finally, we do not know the extent to which natural enemies will suppress whitefly infestations. Ladybirds and parasitic wasps have been listed as predators. Pyrethroid insecticides are applied to Brassica crops to control caterpillars and other pests and these will kill natural enemies. If whiteflies are resistant to pyrethroids then pyrethroid applications may exacerbate the whitefly problem. The aim of the project was to evaluate insecticide spray programmes and application strategies that might improve control of Brassica whitefly. This was addressed through 1) 2012 Agriculture and Horticulture Development Board 7

12 field trials, 2) pot trials and 3) spray application tests in a wind tunnel. Four organisations collaborated to undertake this programme of work: University of Warwick (Warwick Crop Centre), Allium & Brassica Agronomy Ltd, Silsoe Spray Applications Unit (TAG) and Elsoms Seeds. 1. Field Trials on Brussels sprout and kale to evaluate spray programmes (Elsoms, Allium and Brassica Centre, Warwick Crop Centre). The aim of two field trials at Elsoms Seeds trials ground in Spalding was to evaluate a number of spray programmes using approved insecticides together with the application of a novel, coded insecticide product that had looked promising in earlier HDC-funded trials on Brassica aphids (FV 375), where incidental control of whitefly was recorded. The programmes used on Brussels sprout and kale differed because Biscaya (thiacloprid) is not approved on kale. A recent study (Springate & Colvin, 2011) indicated that some populations of whitefly are resistant to pyrethroid insecticides and to investigate this further, Decis (deltamethrin) was applied in two of the programmes in each trial. Materials and methods The two trials were grown at and managed by Elsoms Seeds and treatments were applied by Carl Sharp, Allium & Brassica Agronomy Ltd. Both trials were planted on 16 June For the Brussels sprout trial (cv Doric) there were 4 replicates of 10 treatments. The trial was planted on 0.6m (24 ) rows with 0.55m between plants in the row. Each plot was 4 rows x 12 plants and assessments were undertaken on 20 plants in the two central rows. The whole trial was 10 plots wide (24m) by 4 plots long (26.4m). The treatment programmes and application details are shown in Tables 1.1 and 1.2. Decis was evaluated alone (T2). It was also included in one of the spray programmes to determine any secondary effects it might have on whitefly control through its impact on natural enemies if applied to control caterpillars (T3). Dipel DF was included in a similar programme as a control (T4). All treatments were applied in 300 l water/ha using an AZO compressed air plot sprayer Agriculture and Horticulture Development Board 8

13 Table 1.1. Treatments and application dates in the trial on Brussels sprout 12 Aug 25 Aug 9 Sep 22 Sep Code T1 Untreated Untreated Untreated Untreated Untreated T2 Decis Decis Decis Decis Decis T3 Movento + Decis Biscaya + Decis Movento + Decis Biscaya + Decis MBMB + Decis T4 Movento + Biscaya + Dipel Movento + Biscaya + Dipel MBMB + Dipel Dipel DF DF Dipel DF DF. T5 Plenum Movento Plenum Movento PMPM T6 Biscaya Plenum Biscaya Plenum BPBP T7 Movento Plenum + Movento Plenum + M(PB)M(PB) Biscaya Biscaya T8 Movento Movento Biscaya Biscaya MMBB T9 HDCI 013 Movento HDCI 013 Movento 13M13M T10 HDCI 013 HDCI Agriculture and Horticulture Development Board 9

14 Table 1.2. Products and application rates in the trial on Brussels sprout Product Active ingredient Application rate Water volume Biscaya Thiacloprid 0.4 l/ha 300 l/ha Decis Deltamethrin 0.3 l/ha 300 l/ha Dipel DF Bacillus thuringiensis 1 kg/ha 300 l/ha HDCI 013 Coded product 0.75 l/ha (with Codacide at l/ha l/ha) Movento Spirotetramat 0.5 l/ha 300 l/ha Plenum Pymetrozine 0.4 kg/ha (with Phase II at 1l/ha 300 l/ha For the kale trial (cv Reflex) there were 4 replicates of 8 treatments. The trial was planted on 0.6m (24 ) rows with 0.74m between plants in the row. Each plot was 4 rows x 12 plants and assessments were undertaken on 20 plants in the two central rows. The whole trial was 8 plots wide (19.2m) by 4 plots long (35.5m). The treatment programmes and application details are shown in Tables 1.3 and 1.4. Once again, Decis was evaluated alone (T2). It was also included in the spray programmes to determine any secondary effects it might have on whitefly control through its impact on natural enemies if applied to control caterpillars (T3). Dipel DF was included in a similar programme as a control (T4). All treatments were applied in 300 l water/ha using an AZO compressed air plot sprayer. Table 1.3. Treatments and application dates in the trial on Kale 12 Aug 25 Aug 9 Sep 22 Sep Code T1 Untreated Untreated Untreated Untreated Untreated T2 Decis Decis Decis Decis Decis T3 Movento + Plenum + Decis Plenum + Decis Decis Movento + Decis MPMP + Decis T4 Movento + Plenum + Dipel Movento +Dipel Plenum + Dipel Dipel DF DF DF DF MPMP + Dipel T5 Plenum Movento Plenum Movento PMPM T6 Movento Movento Plenum Plenum MMPP T7 HDCI 013 Movento HDCI 013 Movento 13M13M T8 HDCI 013 HDCI Agriculture and Horticulture Development Board 10

15 Table 1.4. Products and application rates in the trial on Kale Product Active ingredient Application rate Water volume Decis Deltamethrin 0.3 l/ha 300 l/ha Dipel DF Bacillus 1 kg/ha 300 l/ha thuringiensis HDCI 013 Coded product 0.75 l/ha (with 300 l/ha Codacide at 2.5 l/ha) Movento Spirotetramat 0.5 l/ha 300 l/ha Plenum Pymetrozine 0.4 kg/ha (with Phase II at 1l/ha 300 l/ha Assessments In both trials an initial assessment of whitefly numbers was made before treatments were applied and the plots were assessed following each treatment application. Assessments were made of: Number of egg-circles per plant Number of leaves with larvae per plant Number of adults per plant on a scale of 0-4 Assessments were made on 6 plants per plot on: 9 August 16 August 7 September 21 September 4 October Analysis Data were subjected to Analysis of Variance. The data on the number of egg circles and number of leaves with larvae were subjected to a square-root transformation prior to analysis. Results All of the plots were naturally infested with whitefly prior to treatment application (Figure 1.1). Figures 1.2 and 1.3 show the numbers of whitefly of each stage on untreated control plants throughout the Brussels sprout and kale trials respectively. In both trials the infestation increased steadily over time Agriculture and Horticulture Development Board 11

16 Figure 1.1. Whitefly infestation in an insecticide-free plot in the trial on kale Aug 16-Aug 23-Aug 30-Aug 6-Sep 13-Sep 20-Sep 27-Sep 4-Oct Egg circles Leaves with larvae Adults (score) Figure 1.2. The numbers of whitefly of each stage on untreated control plants throughout the Brussels sprout trial 2012 Agriculture and Horticulture Development Board 12

17 Aug 16-Aug 23-Aug 30-Aug 6-Sep 13-Sep 20-Sep 27-Sep 4-Oct Egg circles Leaves with larvae Adults (score) Figure 1.3. The numbers of whitefly of each stage on untreated control plants throughout the kale trial Tables show a summary of the analysis for the Brussels sprout trial and Figures show the data graphically. Egg circles There was a statistically significant effect of programme on the number of egg circles per plant from the second post-spraying assessment (7 September) onwards. All programmes with the exception of Decis, BPBP and reduced the numbers of egg circles compared with the untreated control on 7 and 21 September. All programmes with the exception of Decis and BPBP reduced the numbers of egg circles compared with the untreated control on 4 October. MBMB + Dipel was the most effective programme on 7 and 21 September and MBMB + Decis, M(PB)M(PB) and MMBB were equally effective. M(PB)M(PB) was the most effective programme on 4 October and MBMB + Dipel and MBMB + Decis were equally effective. In general, the most effective programmes started with Movento (M) and included Biscaya (B). The Biscaya/Plenum programme (BPBP) was ineffective throughout, and the programme was ineffective on two occasions Agriculture and Horticulture Development Board 13

18 Number of leaves with larvae In general, programmes that reduced the number of egg circles also reduced the numbers of leaves with larvae. Statistically-significant effects of programmes were seen from the first post-spraying assessment (16 August) when the MBMB + Decis and MBMB + Dipel treatments reduced the number of infested leaves compared with the untreated control. By 7 September, plants treated with programmes including Movento were less infested than the untreated control and the same was true on 4 October when the plants treated with the programme were also less infested than the control. The four most effective programmes all started with Movento and included Biscaya and there was no difference between the three most effective programmes (MBMB + Decis, M(PB)M(PB), MBMB + Dipel), which had reduced the infestation to zero or close to zero by 4 October. Adults Once again, programmes that reduced the number of egg circles and infested leaves also reduced adult numbers. Statistically-significant differences were apparent from 7 September onwards. From this date onwards plants treated with the programmes using Movento and Biscaya were less infested than the untreated control and on 4 October the 13M13M and PMPM programmes were also less infested than the untreated control. The four most effective programmes all started with Movento and included Biscaya and there was no difference between the three most effective programmes (MBMB + Decis, M(PB)M(PB), MBMB+Dipel) Agriculture and Horticulture Development Board 14

19 Table 1.5. Brussels sprout trial Analysis of Variance - mean numbers of egg circles per plant (treatments ranked by level of control on 4 October). Values highlighted in yellow indicate programmes which have reduced the whitefly infestation compared with the untreated control. Values highlighted in green indicate programmes that are also as effective as the most effective treatment. Trans Backtrans Trans Backtrans Trans Backtrans Trans Backtrans Trans Backtrans 09-Aug 16-Aug 07-Sep 21-Sep 04-Oct M(PB)M(PB) MBMB + Dipel MBMB + Decis MMBB M13M PMPM BPBP Untreated Decis Fpr <.001 <.001 <.001 rep d.f l.s.d Agriculture and Horticulture Development Board 15

20 Table 1.6. Brussels sprout trial Analysis of Variance - mean numbers of leaves with larvae (treatments ranked by level of control on 4 October). Values highlighted in yellow indicate programmes which have reduced the whitefly infestation compared with the untreated control. Values highlighted in green indicate programmes that are also as effective as the most effective treatment. Trans Backtrans Trans Backtrans Trans Backtrans Trans Backtrans Trans Backtrans 09-Aug 16-Aug 07-Sep 21-Sep 04-Oct MBMB + Decis M(PB)M(PB) MBMB + Dipel MMBB M13M PMPM BPBP Untreated Decis Fpr <.001 <.001 <.001 rep d.f l.s.d Agriculture and Horticulture Development Board 16

21 Table 1.7. Brussels sprout trial Analysis of Variance - mean numbers of adults (score) (treatments ranked by level of control on 4 October). Values highlighted in yellow indicate programmes which have reduced the whitefly infestation compared with the untreated control. Values highlighted in green indicate programmes that are also as effective as the most effective treatment. 09-Aug 16-Aug 07-Sep 21-Sep 04-Oct M(PB)M(PB) MBMB + Dipel MBMB + Decis MMBB M13M PMPM BPBP Untreated Decis Fpr <.001 <.001 rep d.f l.s.d Mean number of egg circles M(PB)M(PB) MBMB + Dipel MBMB + Decis MMBB 13M13M PMPM BPBP Untreated Decis 09-Aug 16-Aug 07-Sep 21-Sep 04-Oct Figure 1.4. Brussels sprout - number of egg circles per plant (treatments ranked by level of control on 4 October) Agriculture and Horticulture Development Board 17

22 30 Mean number of leaves with larvae M(PB)M(PB) MBMB + Dipel MBMB + Decis MMBB 13M13M PMPM BPBP Untreated Decis 09-Aug 16-Aug 07-Sep 21-Sep 04-Oct Figure 1.5. Brussels sprout - number of leaves with larvae per plant (treatments ranked by level of control on 4 October) Mean number of adults (score) M(PB)M(PB) MBMB + Dipel MBMB + Decis MMBB 13M13M PMPM BPBP Untreated Decis 09-Aug 16-Aug 07-Sep 21-Sep 04-Oct Figure 1.6. Brussels sprout - number of adults per plant (0-4 score) (treatments ranked by level of control on 4 October). Tables show a summary of the analysis for the kale trial and Figures show the data graphically Agriculture and Horticulture Development Board 18

23 Numbers of egg circles per plant There was a statistically-significant effect of programme from the first post-spray assessment (16 August) onwards. Programmes MPMP + Decis, MPMP + Dipel, MMPP and 13M13M all reduced the number of egg circles compared with the untreated control from 16 August onwards. PMPM reduced the number of egg circles on 3 occasions and on one occasion. Generally the most effective programmes included Movento and the two most effective programmes (MPMP + Decis, MPMP + Dipel) started with Movento and provided similar levels of control. Numbers of leaves with larvae There was a statistically-significant effect of programme from the second post-spray assessment (7 September) onwards. Programmes MPMP + Dipel, MPMP + Decis and MMPP all reduced the number of infested leaves compared with the untreated control from 7 September onwards. Programmes 13M13M reduced the number of infested leaves from 21 September onwards and on 4 October. MPMP + Dipel and MPMP + Decis were the two most effective programmes and were equally effective, reducing the infestation to almost zero on 4 October. Adults There was a statistically-significant effect of programme from the second post-spray assessment (7 September) onwards. Programmes MPMP + Dipel, MPMP + Decis and MMPP all reduced the number of adults compared with the untreated control from 7 September onwards. MPMP + Dipel and MPMP + Decis were the two most effective programmes and were equally effective Agriculture and Horticulture Development Board 19

24 Table 1.8. Kale trial Analysis of Variance - mean numbers of egg circles per plant (treatments ranked by level of control on 4 October). Values highlighted in yellow indicate programmes which have reduced the whitefly infestation compared with the untreated control. Values highlighted in green indicate programmes that are also as effective as the most effective treatment. Treatment Trans Backtrans Trans Backtrans Trans Backtrans Trans Backtrans Trans Backtrans 09-Aug 16-Aug 07-Sep 21-Sep 04-Oct MPMP + Decis MPMP + Dipel MMPP M13M PMPM Untreated Decis Fpr <.001 <.001 <.001 rep d.f l.s.d Agriculture and Horticulture Development Board 20

25 Table 1.9. Kale trial Analysis of Variance - mean numbers of leaves with larvae (treatments ranked by level of control on 4 October). Values highlighted in yellow indicate programmes which have reduced the whitefly infestation compared with the untreated control. Values highlighted in green indicate programmes that are also as effective as the most effective treatment. Treatment Trans Backtrans Trans Backtrans Trans Backtrans Trans Backtrans Trans Backtrans 09-Aug 16-Aug 07-Sep 21-Sep 04-Oct MPMP + Dipel MPMP + Decis MMPP M13M PMPM Decis Untreated Fpr <.001 <.001 <.001 rep d.f l.s.d Agriculture and Horticulture Development Board 21

26 Table Kale trial Analysis of Variance - mean numbers of adults (score) (treatments ranked by level of control on 4 October). Values highlighted in yellow indicate programmes which have reduced the whitefly infestation compared with the untreated control. Values highlighted in green indicate programmes that are also as effective as the most effective treatment. 09-Aug 16-Aug 07-Sep 21-Sep 04-Oct MPMP + Decis MPMP + Dipel MMPP M13M PMPM Untreated Decis Fpr <.001 <.001 <.001 rep d.f l.s.d Mean number of egg circles MPMP + Decis MPMP + Dipel MMPP 13M13M PMPM Untreated Decis 09-Aug 16-Aug 07-Sep 21-Sep 04-Oct Figure 1.7. Kale - number of egg circles per plant (treatments ranked by level of control on 4 October) Agriculture and Horticulture Development Board 22

27 30 Mean number of leaves with larvae MPMP + Dipel MPMP + Decis MMPP 13M13M PMPM Decis Untreated 09-Aug 16-Aug 07-Sep 21-Sep 04-Oct Figure 1.8. Kale - number of leaves with larvae per plant (treatments ranked by level of control on 4 October) Mean number of adults (score) MPMP + Decis MPMP + Dipel MMPP 13M13M PMPM Untreated Decis Aug 16-Aug 07-Sep 21-Sep 04-Oct Figure 1.9. Kale - number of adults per plant (0-4 score) (treatments ranked by level of control on 4 October) Agriculture and Horticulture Development Board 23

28 2. Potted plant tests (Warwick Crop Centre) A whitefly culture was established using field-collected insects. The insects were maintained on potted cauliflower plants (cv Skywalker) in a large cage in the Insect Rearing Unit (IRU) at Wellesbourne. Materials and methods Test plants were placed with culture plants and whitefly infestation was allowed to occur naturally. When plants were sufficiently infested they were removed and the numbers of egg circles, larvae and adults were counted. Plants were transferred to the Pesticide Handling Unit at Wellesbourne and sprayed using a hand sprayer with the treatments listed in Table 2.1. Two tests were conducted. Application volumes were calculated assuming a plant measured 10 x 10 cm (0.01 m 2 ) or 30 x 30 cm (= 0.09 m 2 ) in Tests 1 and 2 respectively. With an application volume of 300 l/ha this represents 0.9 or 2.7 ml treatment solution per plant. The hand sprayer was calibrated to deliver approximately 1 ml per squirt. One squirt was applied in Test 1 and 3 squirts were applied in Test 2. Sprays were applied over the top of the plants. For outer leaf treatments the crown of the plant was shielded with a glass beaker (100 ml) and for crown treatments the outer leaves were shielded with paper towels. The test plants were returned to the Insect Rearing Unit and placed in cages (1 plant per cage). Numbers of egg circles, larvae and adults were counted on a number of occasions thereafter. The data were subjected to Analysis of Variance with the pre-spray counts as a covariate Agriculture and Horticulture Development Board 24

29 Table 2.1 Insecticide treatments applied in pot tests at Wellesbourne Number Product a.i. Dose (l/ha) Target 1 Movento Spirotetramat 0.5 Crown 2 Movento Spirotetramat 0.5 Outer leaves 3 Biscaya Biscaya 0.4 Crown 4 Biscaya Biscaya 0.4 Outer leaves 5 Untreated Results On untreated control plants in Test 1, numbers of all stages increased over the course of the test. Both Movento treatments and the Biscaya-Crown treatment reduced larval numbers on all three assessment occasions compared with the untreated control (Table 2.2; Figure 2.1). The Biscaya-Outer treatment was less effective and reduced larval numbers on the first assessment occasion only (11 DAT). In terms of adult control, there was no treatment effect 20 days after spraying, but a statistically significant effect 33 days after spraying when numbers on all but the Biscaya-Outer treatment were reduced compared with the control (Table 2.3; Figure 2.2). There was no statistically-significant effect of treatment on egg numbers (Table 2.4). Table 2.2. Numbers of whitefly larvae in Test 1. Counts 11, 20 and 33 days after treatment (DAT) after analysis with pre-spray counts as a covariate. Numbers of larvae per plant Treatment 11 DAT 20 DAT 33 DAT Movento-Crown Movento-Outer Biscaya-Crown Biscaya-Outer Untreated Fpr s.e.d d.f l.s.d Agriculture and Horticulture Development Board 25

30 2500 Number of larvae/plant Movento-Crown Movento-Outer Biscaya-Crown Biscaya-Outer Untreated Days after spraying Figure 2.1 The change in numbers of whitefly larvae on cauliflower in Test 1 after spraying with Biscaya and Movento. Table 2.3. Numbers of whitefly adults in Test 1. Counts 20 and 33 days after treatment (DAT) after analysis with day 11 counts as a covariate. Numbers of adults per plant Treatment 20 DAT 33 DAT Movento-Crown Movento-Outer 25 1 Biscaya-Crown Biscaya-Outer Untreated Fpr s.e.d d.f. 9 9 l.s.d Agriculture and Horticulture Development Board 26

31 300 Number of adults/plant Movento-Crown Movento-Outer Biscaya-Crown Biscaya-Outer Untreated Days after spraying Figure 2.2. The change in numbers of whitefly adults on cauliflower in Test 1 after spraying with Biscaya and Movento. Table 2.4. Numbers of whitefly eggs in Test 1. Counts 11 and 20 days after treatment (DAT) after analysis with pre-spray counts as a covariate. Numbers of eggs per plant Treatment 12 DAT 20 DAT Movento-Crown Movento-Outer Biscaya-Crown Biscaya-Outer Untreated Fpr s.e.d d.f. 9 9 l.s.d On untreated control plants in Test 2, numbers of larvae and adults decreased over the course of the test. Egg numbers did not change much. There were no statistically-significant effects of treatment on any development stage (Tables ) Agriculture and Horticulture Development Board 27

32 Table 2.5. Numbers of whitefly larvae in Test 2. Counts 14 and 22 days after treatment (DAT) after analysis with pre-spray counts as a covariate. Numbers of larvae per plant Treatment 14 DAT 22 DAT Movento-Crown Movento-Outer Biscaya-Crown Biscaya-Outer Untreated Fpr s.e.d d.f. 9 9 l.s.d Table 2.6 Numbers of whitefly adults in Test 2. Counts 7, 14 and 22 days after treatment (DAT) after analysis with pre-spray counts as a covariate. Numbers of adults per plant Treatment 7 DAT 14 DAT 22 DAT Movento-Crown Movento-Outer Biscaya-Crown Biscaya-Outer Untreated Fpr s.e.d d.f l.s.d Table 2.7 Numbers of whitefly eggs in Test 2. Counts 14 and 22 days after treatment (DAT) after analysis with pre-spray counts as a covariate. Numbers of eggs per plant Treatment 14 DAT 22 DAT Movento-Crown Movento-Outer Biscaya-Crown Biscaya-Outer Untreated Fpr s.e.d d.f. 9 9 l.s.d Agriculture and Horticulture Development Board 28

33 3. Spray application tests Examine spray deposition patterns with different application systems in the wind tunnel on the Silsoe site (Silsoe Spray Applications Unit (TAG), Allium and Brassica Centre). Whitefly colonies are typically found on the undersides of crop leaves and therefore pose a difficult target for the application of spray chemicals with a contact mode of action. This preliminary study aimed at using the controlled conditions in a wind tunnel to examine the extent to which the undersides of crop leaves could be targeted in the crops of Brussels sprout and kale using boom mounted application systems that could be easily configured on conventional machines. The work addressed the application variables relating to: nozzle designs; application volumes; forward speeds; wind speeds during application. It was recognised that many growers would have access to conventional boom sprayers and would be keen to adopt technologies that could be readily implemented using such machines while maintaining relatively high work rates. Materials and Methods Experimental conditions used in the study The work was conducted using mature Brussels sprout and kale plants grown in pots by The Allium and Brassica Centre and transported to the wind tunnel on the Silsoe site operated by NIAB TAG. A three by three matrix of plants was set up in the working section of the tunnel simulating crop rows spaced at 61 cm and with plants spaced at 48 cm within the row (Figure 3.1). Outer plants within the matrix were positioned to act as guards such that the central plant could be treated and sampled in a way that was representative of the field condition. It was initially planned to mount 16 mm diameter circular plastic discs on both the upper and lower sides of sample leaves at three levels on this central plant using a contact adhesive in such a way that these could be removed after spraying and deposits of a tracer dye recovered and quantified by spectrophotometry. However, preliminary experiments conducted with cut, rather than pot grown, sprout plants showed that the distribution of spray deposits on the undersides of crop leaves was at a very low level and distributed unevenly such that quantifying such deposits in a meaningful way based on disc samples would be very difficult and require a very large number of samples. It was therefore 2012 Agriculture and Horticulture Development Board 29

34 decide to record deposition patterns by spraying a fluorescent tracer dye, illuminating treated leaves with an ultra-violet light and recording levels of coverage photographically. Sample leaves were taken from three levels up the plant, (top, middle and bottom) and at each level two leaves were taken from the front of the plant (i.e. facing the direction of sprayer travel) and from the side. Photographs were then taken of the upper and lower leaf surfaces in each case. Figure 3.1. Arrangements of kale plants in the working section of the wind tunnel. An electrically operated transporter mechanism was mounted from the roof of the working section in the tunnel that enabled a small boom arrangement fitted with three nozzles at 0.5 m spacing to be moved down the tunnel at controlled speeds of up to 12 km/h. Speed was measured electronically by micro-switches on the transporter and adjusted on the system control unit. Nozzle systems were selected to give a range of droplet sizes and delivery angles that might achieve under-leaf deposits and the nozzles used are summarised in Table Agriculture and Horticulture Development Board 30

35 Table 3.1. Nozzle conditions used in the study Nozzle type Pressure, Forward speed, Application bar km/h volume, L/ha Conventional flat fan Conventional flat fan Conventional flat fan Twin angled air-induction GAT Twin angled air-induction GAT Angled nozzle 05 potato Angled nozzle 05 potato Twin cap 2 of flat fan Twin cap 2 of flat fan Hollow cone (DC 04:CR25) Hollow cone (DC 04:CR25) Dropleg with flat fan Dropleg with Delavan Cone nozzle Dropleg with TX12 cone nozzle Dropleg with TX12 cone nozzle Dropleg with TX26 cone nozzle Changes to nozzle angle and the use of a small droplet size were considered to be the key potential variables in achieving under-leaf coverage and hence the nozzles listed in Table 3.1 varied these two parameters based on commercially available designs. Each nozzle design was operated at two nominal application volumes (200 and 400 L/ha) by using forward speeds of 6.0 and 12.0 km/h. Nozzles were positioned 400 mm above the top of the crop this being the lowest height at which a uniform volume distribution pattern could be maintained with nozzles having a spray fan angle of 110 o. Results from the initial nozzles used, spraying from above the crop, gave very low levels of under-leaf coverage (see also Results section). It was therefore decided to add treatments based on droplegs recognising that because they involved elements running within the crop, they would be mechanically more difficult to arrange and would risk damage to both the spraying units and the crop during typical operations. Typical arrangements of the dropleg systems as operated in the wind tunnel are shown in Figure 3.2. Nozzles for use in conjunction with the dropleg system aimed to create a small droplet size using cone nozzle designs or projecting the spray upwards using a narrow angle flat fan nozzle Agriculture and Horticulture Development Board 31

36 Figure 3.2. Dropleg system installed in the wind tunnel for use in simulated kale (left) and Brussels sprout (right) crops. Most experiments were conducted by spraying into a simulated wind speed of 2.0 m/s since in practice it is unlikely that most applications would be made in still air conditions. Some observations were also made in still air conditions and in a higher wind speed of 4.0 m/s. Experimental methodology All nozzles except those used with the dropleg system were installed in standard nozzle holders mounted on the small boom arrangement attached to the transporter. Nozzles were supplied with a spray liquid that comprised of a fluorescent tracer dye and 0.1% of a surfactant (Tween 20) from a pressurized stainless steel canister. Most of the work used a pink fluorescent tracer dye but some observations were also made with a yellow dye with the aim of increasing the contrast between the deposits and the background fluorescence of leaves. Because the tracer dyes were suspensions rather than solutions, agitation was important. The canisters were therefore shaken well before each spraying run so as to deliver a constant concentration of tracer dye to treated plants and enable direct comparisons of deposits from photographs. Spraying pressure was measured using an electronic transducer positioned close to the boom and was controlled and adjusted by varying the compressed air pressure in the canister using a diaphragm valve. At the start of a series of spray runs, the feed pipes to the nozzles were purged to ensure that there was no air in the system. Plants were then arranged in the working section of the tunnel as described above and sprayed with a given treatment. Once treated, the central plant in the matrix was carefully removed from the tunnel to avoid disturbing any of the deposit and placed in an undisturbed area of the laboratory so that deposits could dry Agriculture and Horticulture Development Board 32

37 Sample leaves were then removed from the top, middle and lower parts of the treated plant and taken to a dark room where they were illuminated by ultra-violet lights positioned above and to the side of the leaf. Photographs of the deposit were then taken with a fixed camera position and a long time exposure (10 to 30 seconds depending on conditions). Photographs were then filed electronically and catalogued for subsequent analysis. Results Observations of deposits achieved with nozzles that were fitted in standard nozzle holders Treatments applied with the 05 conventional flat fan nozzle operating at forward speeds of 6.0 and 12.0 km/h to apply volumes of 400 and 200 L/ha respectively were used as comparative references for the work. Coverage on upward facing surfaces was generally good both at the top of the crop in both Brussels sprout and kale (Figure 3), and in the case of the Brussels sprout crop, there was good evidence of penetration into the canopy and deposits on the upper facing surfaces of leaves, stems and buttons. However, there was very little coverage of the undersides of leaves except where there was some curling upwards at the edge of a leaf with the Brussels sprout plants (Figure 3.4) Agriculture and Horticulture Development Board 33

38 Figure 3.3. Deposits were achieved on upward facing leaves at the top of the crop (upper photograph) with penetration of spray down the plant in Brussels sprout giving deposits on the upper parts of buttons and leaf stalks (lower photographs) using an 05 conventional nozzle applying 300 L/ha in preliminary spraying runs at 8.0 km/h Agriculture and Horticulture Development Board 34

39 Figure 3.4. The upper and lower surfaces of a leaf from the upper part of a treated Brussels sprout plant showing the difference in deposit on these two surfaces plants treated with a conventional 05 flat fan nozzle applying 300 L/ha at 8.0 km/h. The photographs in Figures 3.3 and 3.4 show that the leaves of the Brussels sprout plant tended to fluoresce with a blue colour such that the contrast with the spray deposits was less than originally expected. Abrasions on the under-leaf surface due to the presence of whitefly colonies could be clearly seen under the ultra-violet light because of the different fluorescent characteristic. With both Brussels sprout and kale plants, deposits tended to be observed at all levels in the crop although those at the lowest levels were generally lower and more variable due to the shading effect of leaves higher up the plant. The tightly curled nature of the kale leaves meant that deposits on upper leaf surfaces were less easily visualised (Figure 3.5) and this, together with the larger downward leaves of the kale plants resulted in even lower under-leaf deposits than was the case with the Brussels sprout plants. Deposits on the upper leaf surfaces at the mid-plant height were often high in kale particularly where leaves protruded outwards beyond those at the top of the canopy. The use of twin caps provided sprays that were both finer (smaller droplet size associated with the use of two smaller conventional flat fan nozzles) and delivered at angles both forward and backwards in the direction of travel. Deposit distributions in both Brussels sprout and kale plants were similar to those obtained with the conventional 05 flat fan nozzle treatments with no evidence of a substantial increase in the under-leaf coverage obtained see example in Figure Agriculture and Horticulture Development Board 35

40 Figure 3.5. Upper and lower surfaces of a leaf taken from the mid-plant height in kale treated with the 05 conventional nozzle applying 400 L/ha. Figure 3.6. Upper and lower surfaces of a leaf taken from the mid-plant height in kale treated with the twin cap nozzles applying 400 L/ha. The Guardian Air Twin nozzle (Hypro EU Ltd) also delivered sprays angled forwards and backwards in the direction of travel but in this case the nozzles are of an air-induction design such that the droplets are larger than from conventional nozzles and have air inclusions within the droplets generated by the nozzle. As with the twin caps, deposit 2012 Agriculture and Horticulture Development Board 36

41 distributions were similar to those obtained with the 05 conventional flat fan nozzles with no evidence of a substantial increase in under-leaf deposits. The potato nozzle (Syngenta Crop Protection Ltd) uses a standard variable pressure nozzle tip that is mounted at an angle such that the spray is delivered at 30 o to the vertical. The angled spray is designed to give more mixing within the potato crop canopy and hence increased deposition including on the undersides of leaves. A common configuration is to mount nozzles alternately forwards and backwards to reduce the risk of drift while maintaining high levels of mixing within the canopy. For this work using three nozzles on the small boom, the centre nozzle was directed forwards and the outer two directed backwards. Observed deposits were again similar to those seen with the other nozzle systems with no evidence of substantial increases in under-leaf deposits using these nozzles. The cone nozzles were used as a way of delivering relatively small droplets that would have relatively low velocities when leaving the nozzle such that air movements may then carry droplets into the canopy. Results of the observations with treatments applied to both kale and Brussels sprout plants with cone nozzles again showed no substantial increase in the under-leaf deposits although there was some evidence of different spray behaviour with the Brussels sprout plants with higher deposits on upper leaf surfaces more exposed to air movements. The effect of air movement was further examined by conducting a run with the twin angled air induction nozzle in a wind speed of 4.0 m/s. While this showed some trends towards increased under-leaf deposits, these deposit levels were still very considerably below those that would be needed to give acceptable levels of control with contact acting insecticides and the risk of drift associated with operation in such wind speeds would be commercially unacceptable. There would also be issues relating to spraying windows if applications could only be made in high wind conditions. Observations of deposits achieved with nozzles that were fitted in drop leg nozzle holders Because very low levels of under-leaf coverage were observed with all of the application systems based on a conventional boom sprayer, it was decided to examine what might be achieved using droplegs fitted with different nozzle systems. Commercial designs of dropleg were mounted on the spray boom with one leg either side of the central plant in the matrix. Cone nozzles were used in most of the runs so that droplets would be deposited in the canopy. The results from runs with the dropleg configuration showed a substantial increase in under-leaf deposits although the level and distribution of such deposits did not 2012 Agriculture and Horticulture Development Board 37

42 consistently match those on upper leaf surfaces treated with nozzles operating above the crop. The shading effect of adjacent leaves within the canopy was evident in many situations particularly at levels away from the mid-plant level at which the nozzles were mounted. Examples of the coverage obtained with the dropleg systems operating in Brussels sprout are shown in Figures 3.7, 3.8, 3.9 and Figure 3.7. Upper (left) and lower (right) surface deposits for a leaf taken from the mid-plant height in Brussels sprout treated with the dropleg system fitted with a Delavan wide angled cone nozzle operating to apply 164 L/ha. Figure 3.8. Upper (left) and lower (right) surface deposits for a leaf taken from the mid-plant height in Brussels sprout treated with the dropleg system fitted with a TX26 cone nozzle operating to apply 360 L/ha Agriculture and Horticulture Development Board 38

43 Figure 3.9. Upper (left) and lower (right) surface deposits for a leaf taken from the top of the plant height in Brussels sprout treated with the dropleg system fitted with a TX26 cone nozzle operating to apply 360 L/ha. Figure Upper (left) and lower (right) surface deposits for a leaf taken from the midplant height in Brussels sprout treated with the dropleg system fitted with a TX26 cone nozzle operating to apply 360 L/ha as Figure 3.8 but with a yellow rather than pink dye. The results with Brussels sprout plants shown in Figures 3.7 to 3.10 indicate: that in the centre of the plant under-leaf coverage was generally good when operating with a system to apply more than 200 L/ha although deposits on upper leaf surfaces then tended to be lower as expected; deposits at the top of the plant were reasonably good on under-leaf surfaces but were low on upper leaf surfaces: this could (and has been) addressed in practical arrangements by using a combination of dropleg and overhead applications; at least 200 L/ha is required if good coverage on upper and lower leaf surfaces is to be achieved; 2012 Agriculture and Horticulture Development Board 39

44 the use of a different coloured tracer dye can alter the contrast between spray deposits and the background colour of leaves illuminated under ultra-violet light. In kale the droplegs were less effective and low levels of under-leaf coverage were achieved probably as a result of leaf shape, size and orientation see Figures 3.11 and Figure Upper (left) and lower (right) surface deposits for a leaf taken from the midplant height in kale treated with the dropleg system fitted with a TX26 cone nozzle operating to apply 360 L/ha. Figure 3.11 shows that at the mid-plant height spray was deposited on the upper sides of leaves probably due to spray movement between the plants but little of the spray has penetrated to be deposited on the undersides of the kale leaf. Similar effects are seen at the top of the canopy Figure Figure Upper (left) and lower (right) surface deposits for a leaf taken from the top of the plant height in kale treated with the dropleg system fitted with a TX26 cone nozzle operating to apply 360 L/ha Agriculture and Horticulture Development Board 40