Project title:€¦ · Web viewProject title: Lettuce: Further development of ‘Best Practice’...
Transcript of Project title:€¦ · Web viewProject title: Lettuce: Further development of ‘Best Practice’...
Project title: Lettuce: Further development of ‘Best
Practice’ for disease control in protected
and outdoor crops
Project number: FV/PE 410
Project leader: Dr G M McPherson, STC
Report: Final Report, January 2016
Previous report: Annual Report, July 2015
Key staff: Mr J Townsend, STC
Mr A Ormerod, STC
Dr E Wedgwood, ADAS
Ms A Huckle, ADAS
Mr T Boor, ADAS
Location of project: Stockbridge Technology Centre Research
Foundation, Cawood, North Yorkshire.
ADAS, Boxworth, Cambridge
Industry Representative: David Norman, Independent Consultant
Colin Bloomfield, Independent Consultant
Geoffrey Smith, Mapleton Growers
Date project commenced: 01 August 2012
Date project completed
(or expected completion date):
31 January 2016
Agriculture and Horticulture Development Board 2023. All rights reserved
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
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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.
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AUTHENTICATIONWe 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.
James Townsend
Project Manager
Stockbridge Technology Centre Research Foundation
Signature ............................................................ Date ............................................
Timothy Boor
Plant Pathologist
ADAS UK Ltd
Signature ............................................................ Date ............................................
Angela Huckle
Horticulture Consultant
ADAS UK Ltd
Signature ............................................................ Date ............................................
Report authorised by:Dr G M McPherson
Science Director
Stockbridge Technology Centre Research Foundation
Signature ............................................................ Date ............................................
Dr E Wedgwood
Plant Pathologist
ADAS UK Ltd
Signature ............................................................ Date ............................................
Agriculture and Horticulture Development Board 2023. All rights reserved
CONTENTS
Headline..................................................................................................................5
Background.............................................................................................................5
Summary.................................................................................................................5
Financial Benefits..................................................................................................11
Action Points.........................................................................................................12
Introduction...........................................................................................................14
Materials and methods..........................................................................................16
Results and Discussion.........................................................................................31
Conclusions...........................................................................................................58
Knowledge and Technology Transfer....................................................................59
References............................................................................................................59
Appendices..............................................................Error! Bookmark not defined.
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GROWER SUMMARY
Headlines
Outdoor lettuce Both Fubol Gold and Revus were consistently effective against downy mildew at the final
spray timings in different spray programmes.
Some biopesticide products were demonstrated to be as effective as conventional
fungicides at certain timings within a fungicide programme.
Products with activity against powdery mildew were as effective at half rate compared to full
rate (in a low disease situation).
Whilst none of the novel fungicide programmes evaluated were significantly better than the
current commercial programmes, the addition of novel mode of action products would help
with resistance management and protect existing active substances for the long-term.
Protected Lettuce A reduction in the application rate of active ingredients using tank mixes, allowed broader
disease control without compromising overall efficacy. This helped reduce the risk of
pesticide residues at harvest and minimises the risk of resistance development in pathogen
populations.
The inclusion of alternative Oomycete fungicides e.g. mandipropamid (Revus) helped
control metalaxyl resistant strains of Bremia lactucae.
Whilst downy mildew is a key target, broad spectrum fungicide programmes are needed to
provide effective control of other lettuce pathogens.
Products effective against Sclerotinia sclerotiorum also proved to be effective against
Sclerotinia minor.
Background
Downy mildew (Bremia lactucae) is responsible for most losses in outdoor and protected
lettuce. Soil-borne pathogens, such as Sclerotinia, Botrytis and Rhizoctonia are also
important and contribute to significant losses in some crops. Sclerotinia causes severe head
decay, especially near maturity whilst bottom rot (Rhizoctonia solani) tends to affect the
lower leaves (predominantly in protected crops) that can render affected plants
unmarketable. Grey mould (Botrytis cinerea) is often present on the older damaged leaves
(including those infected by Bremia) and is usually removed during trimming, though in wet
seasons severe infections can reduce head weight significantly.
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The primary purpose of this project was to identify and evaluate novel fungicides and
biopesticides with good activity against the primary lettuce pathogens and to see if there
was ‘incidental’ activity against the more minor pathogens that occur sporadically. Work
also aimed to determine if control could be maintained with reduced application rates to
minimise the risk of residues at harvest whilst ensuring minimal risk of resistance
development.
Summary
Initial Fungicide & Biopesticide ScreeningLaboratory screening tests with novel active ingredients, including new SDHI fungicides, for
activity against downy mildew, Botrytis, Rhizoctonia, Sclerotinia spp. identified a number of
novel active substances capable of inhibiting pathogen growth. Many of the SDHIs
provided good to excellent inhibition of Rhizoctonia and Sclerotinia though, perhaps
surprisingly, were less effective against Botrytis in vitro. Some well-established products
inhibited Botrytis growth as well as Rhizoctonia (iprodione e.g. Rovral), and Sclerotinia
(prochloraz e.g. Octave). HDC F158 inhibited all three pathogens, but was most effective
against Sclerotinia. Fungicides containing metalaxyl and dimethomorph provided good
inhibition of the Oomycete Phytophthora (used as a Bremia surrogate). Infinito (fluopicolide
+ propamocarb hydrochloride) also provided a good inhibition of Oomycetes. The
information gleaned from the laboratory screen helped to design a range of experimental
fungicide programmes in replicated field & glasshouse trials.
Field & Glasshouse trialsA range of outdoor (ADAS) and protected (STC) lettuce trials were completed; the details of
which are outlined in Table 1 below:-
Table 1 Trial schedule for outdoor & protected lettuce cropsTrial Type Site Crop
periodYear Main disease
presentReported
Field Crops(ADAS)
Grower site, Norfolk Aug - Oct 2012 Downy mildew July 2013Grower site, Staffs April - June 2013 Botrytis July 2013Grower site, Lincs Aug - Oct 2013 Downy mildew July 2014Grower site, Kent Aug - Oct 2014 Downy Mildew January 2016Grower site, Lincs July – Oct 2015 Botrytis January 2016
Glasshouse Crops(STC)
STC, Yorkshire Oct - Dec 2012 Downy mildew, Sclerotinia
July 2013
STC, Yorkshire May - June 2013 Botrytis July 2013Grower site, Yorks Mar - May 2014 Sclerotinia minor July 2014STC, Yorkshire Aug – Sept 2014 Rhizoctonia January 2016STC, Yorkshire Sept – Nov 2015 Botrytis January 2016
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Outdoor trialsFive replicated trials were conducted during 2012-2015. All the trials were conducted on
commercial farms so they relied on natural pathogen invasion rather than artificial
introduction.
Disease levels in crops varied between sites and seasons, as might be expected, but the
predominant disease was downy mildew with Sclerotinia and grey mould occurring in some
cases. Other pathogens, where present, were generally at low to trace levels only.
In autumn 2012 downy mildew was the prevalent disease with Botrytis affecting plants
secondarily. There were significant differences between treatments for the control of downy
mildew and four of the treatment programmes looked particularly promising. Unsurprisingly
perhaps, the most effective programmes for downy mildew control were based on products
already approved for use on lettuce and included Fubol Gold (mancozeb + metalaxyl M),
Revus (mandipropamid), Previcur Energy (fosetyl-aluminium + propamocarb hydrochloride)
and Paraat (dimethomorph). There were no significant differences between treatment
programmes for control of Botrytis or in terms of marketable yield.
In spring 2013 a site with a history of Sclerotinia was used, including crop covers, to
increase disease risk. There was a high incidence and moderate severity of Botrytis but
only low levels of Sclerotinia. No downy mildew or ringspot developed in the trial. There
was significantly more Botrytis in treatments that received Signum at the first application.
Whilst the exact reason for this is unclear, it may relate to a slight phytotoxic response thus
predisposing the treated plants to colonisation by this opportunist pathogen. As Sclerotinia
levels remained low there were no significant treatment effects. Treatment 10, which
contained products for downy mildew control at each application and HDC F151 in a tank
mix at the second application, had a significantly lower incidence of Botrytis and a lower
Botrytis severity than all the other treatments.
In autumn 2013 downy mildew was particularly severe with over 70% leaf area affected by
the disease in the untreated control at the harvest assessment. Botrytis was also present
colonising plants secondarily. The most effective programme overall was Revus applied at
all four application timings in combination with HDC F145 though unfortunately this is not a
viable commercial programme. Amistar + Karamate / Previcur Energy / Infinito / Revus in a
programme was almost as effective and provides a wider range of actives, beneficial for
resistance management. This programme also included broad spectrum products (Amistar
+ Karamate) to help control Botrytis and other incidental pathogens. There were no
significant differences between treatment programmes for control of Botrytis. There was
though a trend for Switch, Karamate and Amistar at the T1 and T2 timings to improve
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control. Some treatment programmes significantly improved marketable head weight and
average weight/head.
In autumn 2014 useful information was gained on product efficacy and spray programmes
for the control of downy mildew in a low disease situation. Downy mildew was the main
disease in the trial. Botrytis and Sclerotinia were present and identifiable on the lower
leaves; though no significant treatment effects were noted. The spray programme based on
the previous trial results [Amistar (azoxystrobin), Karamate (mancozeb), Signum (boscalid +
pyraclostrobin), Invader (dimethomorph + mancozeb), Infinito (fluopicolide + propamocarb
hydrochloride), Fubol Gold (mancozeb + metalaxyl-M) and Revus (mandipropamid)] was
one of the most effective treatments. The novel product F147 gave the overall best control
of downy mildew. The use of biofungicides was also evaluated and, in this low disease
situation, F145 gave equivalent control to the conventional fungicide Revus when applied as
the fifth spray in a programme. Where another biofungicide (F188) was used there were
25% more heads affected demonstrating that whilst such products may have potential
further understanding of their timing and placement is needed to inform their practical use in
commercial programmes.
In autumn 2015 the primary aim of the trial was to target downy mildew, but this pathogen
failed to develop. Instead, due to the dry conditions, powdery mildew occurred and useful
information on this target was collected. A total of eight products were investigated, each
applied at full and half rate to compare their relative efficacy. The main disease present at
harvest was Botrytis, with over 90% of plants affected in some treatments. As most
treatments selected for this trial targeted downy mildew, they failed to provide significant
control of Botrytis with no consistent treatment trends observed. With respect to powdery
mildew, there were significant treatment effects with Amistar (azoxystrobin), Fenomenal
(fenamidone + fosetyl-aluminium), F145 (experimental biological) and F145 + Revus
(mandipropamid). The performance of F145 on powdery mildew on lettuce was promising
within this project and this supports data collected in the SCEPTRE project (CP 077) on
other crops.
In most of the outdoor trials pesticide residues remained below the limit of detection though,
in the autumn 2015 trial residues were found two weeks after the final application timing for
certain actives, with the majority of residues being from the dithiocarbamate products.
None of the levels were above MRLs and most were detected at <5% MRL values, however
this result does highlight the importance of the positioning of certain products in the spray
programme.
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Protected TrialsFive replicated trials were conducted during 2012-2015. The majority of the trials were
conducted at STC though one trial specifically targeting Sclerotinia minor was conducted on
a commercial nursery. Where trials were conducted at STC efforts were made to use the
same glasshouse to build up soil inoculum levels and to manipulate pathogen occurrence
through artificial inoculation. Disease levels in crops varied between seasons, as might be
expected, but the predominant disease was downy mildew with Rhizoctonia, Sclerotinia and
Botrytis occurring in some cases. Other diseases, where present, were generally at low to
trace levels only.
The autumn 2012 downy mildew and Botrytis infected the crop early and Sclerotinia
developed at moderate to severe levels and artificial inoculation was not required. The level
of Rhizoctonia in the trial was surprisingly low and ultimately Sclerotinia was responsible for
most of the plant losses. There were significant differences between treatments for downy
mildew, Sclerotinia and the number of dead plants in the trial. The standard commercial
programme (Amistar/Fubol Gold/Teldor/Revus) provided the best control of downy mildew,
but it performed poorly against Botrytis and below average against Sclerotinia. One of the
commercial programmes (Fubol Gold/Signum/Switch/Serenade) provided the best overall
control of the three pathogens that predominated. Encouragingly, three of the experimental
programmes also performed well against these target pathogens. In terms of developing
effective fungicide programmes to control such a broad range of target pathogens this first
trial clearly demonstrated the challenges faced by growers.
In spring 2013 downy mildew didn’t develop in the trial crop though there were high levels of
Botrytis and moderate levels of Rhizoctonia and Sclerotinia. In assessments it proved
difficult to determine the primary cause of plant loss in some cases and, as such, the results
require cautious interpretation. Amistar was included early in some programmes (primarily
to control Rhizoctonia) for a comparative evaluation with Basilex pre-planting. There were
significant differences between treatments for Rhizoctonia and Sclerotinia control at all
assessments and these differences remained fairly consistent. Programmes that had
Amistar, Fubol Gold and Paraat in common had significantly fewer dead plants at the end of
the trial and a significantly greater number of marketable heads than the industry standard.
These results suggest that by using these products in tank mixes at the correct timings, it
should be possible to exclude the use of Basilex as a pre-planting treatment. Some low
levels of pesticide residues were recorded at the end of the trial, but these were below the
MRLs with the exception of HDC F152, which has an MRL in lettuce of 0.01 mg/kg (the limit
of detection).
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In spring 2014 a commercial nursery with soil-borne Sclerotinia minor was used to evaluate
a range of novel fungicides and biocontrol products and to determine whether products
active against S. sclerotiorum were also effective against S. Minor. The trial included
several straight fungicide treatments, both approved and experimental, as well as
programmes based on both commercially available and experimental products. Contans
(Coniothyrium minitans) was applied as a pre-planting treatment on its own and also before
all of the treatment programmes. The QoI fungicides Amistar and Signum as straight
applications provided most effective control of S. minor. However, when the same products
were applied as part of a programme disease control was compromised. Further work is
required to develop effective fungicide programmes where Sclerotinia minor occurs.
Contans reduced S. minor slightly, but this was not significantly different from the untreated.
A number of the experimental products also controlled S. minor well, though were less
effective than Amistar or Signum.
In autumn 2014 a lettuce crop at STC established well though disease symptoms were not
noted until three weeks after planting. The main pathogen was Rhizoctonia which
developed to severe levels and was responsible for extensive plant death. Sclerotinia
infection was also moderate-high though whilst infection didn’t arise until later (on the
necrotic leaf margin tissues) the combination of these two aggressive pathogens killed
many of the trial plants by the end of the study. Downy mildew ranged from 10% to 50%
plants infected depending on treatment but the overall infection severity was low. Botrytis
levels were very low, though may have been masked by the high levels of Rhizoctonia and
Sclerotinia. Phytotoxicity occurred with T11 (HDC F159) but plants soon recovered and it
wasn’t considered sufficiently damaging to halt work with the product.
Control of both Rhizoctonia and downy mildew was good in the first two assessments with
programmes containing a combination of Contans, Amistar, Fubol Gold, Paraat and an
SDHI product e.g. boscalid (in Signum) and significant differences were apparent.
However, by the later stages of the trial both Rhizoctonia and Sclerotinia levels were
exceptionally high and many of the trial plants died due to disease. As such, there were no
significant differences between treatments for any of the diseases assessed at crop
maturity.
The most effective control of Rhizoctonia was achieved with spray programmes that
included Amistar or an SDHI fungicide. This reflects the results seen in the spring 2013
trial.
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Autumn 2015
The Autumn 2015 trial focused on downy mildew though, ironically, the disease was
sporadic this season. A Bremia inoculated split plot trial used two (Cobham Green & Brian)
to increase the risk from the disease. Yet, even after repeated inoculation, unfavourable
weather prevented development of the disease until late in the trial period. In order to
salvage some data the crop was retained for approximately 2 weeks beyond maturity.
No downy mildew was recorded on the commercial variety, Brian, demonstrating the
importance of resistance genes incorporated into modern varieties. There was low to
medium incidence of downy mildew on Cobham Green in the untreated plots and all of the
treatment programmes provided effective control of the disease with very low incidence in
some treatments, including where half rates had been applied. This potentially represents
significant cost savings and should help reduce the risk of both residues and resistance risk.
The incidence of Botrytis in cv. Cobham Green was medium-high, primarily affecting the
outer leaves, but there were no significant differences between treatments. Incidence of
Botrytis in the variety Brian was low-medium, only affecting lower leaves of the crop; again
there were no significant differences between treatments. Rhizoctonia and Sclerotinia also
occurred in both varieties, but at insignificant levels. It is interesting to note that whilst there
were no significant differences in disease incidence or severity between treatments in the
cv. Brian, there were significant differences in mean head weights at harvest. This could
potentially relate to improvements in leaf greening or perhaps relates to the suppression of
incidental soft-rot pathogens on the basal leaves in the crop.
Financial Benefits (Outdoor & Protected Crops)
This project has demonstrated that reduced fungicide rates can potentially be used
effectively in low disease (especially downy mildew) situations and at early spray
timings for disease control and this not only helps in reducing spraying costs but can
potentially also minimise residues at harvest and reduce resistance development to
protect active substances for future use.
Lower residue risk products, including biopesticides, can potentially be integrated into
spray programmes in low disease situations but, in high disease risk situations it is
important to maintain an effective preventative fungicide programme using
manufacturer recommended dose rates. It is too early to determine if this would result
in cost-savings to the grower but there could be other indirect benefits in this approach
that could add value to the produce.
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Action Points (Outdoor & Protected Crops)
Make full use of cultivar resistance, where available, to reduce reliance on conventional
fungicide application, especially for disease like downy mildew and avoid increasing
selection pressure through use of monocultures where possible.
Monitor crops regularly and consider disease risk carefully relative to prevailing climate
locally and according to the weather forecast. Remember that for downy mildew
especially, it is important to apply products preventatively in advance of symptom
expression for effective control.
If weather conditions are conducive to disease i.e. cool & wet and there is known
disease, especially downy mildew, in the area use products at the manufacturers
recommended rates, choosing products particularly active against downy mildew. If
other pathogens are suspected, include alternative products in the spray programme to
broaden the spectrum of activity.
If the weather is not conducive to disease consider reducing rates of application and
using tank mixes to broaden the spectrum of activity of the spray programme.
Be aware of the different mode of action groups for fungicides and avoid over-use of
those regarded as moderate-high risk of resistance development. Either alternate or
tank mix products from different mode of action groups to minimise any risk. For
detailed information of fungicide groups and resistance risk see
http://www.frac.info/docs/default-source/publications/frac-code-list/frac-code-list-
2016.pdf?sfvrsn=2
There are significant restrictions on the timing of application of some products e.g.
dithiocarbamates so it is imperative these are used effectively early in crop
development to minimise any risk of pesticide residues at harvest.
Where there is a risk of other diseases consider using products with broad-spectrum
activity (noting that most downy mildew products are specific to Oomycete organisms)
and won’t provide effective control of pathogens like Botrytis, Sclerotinia & Rhizoctonia.
Whilst there is still much to learn about the use and effectiveness of biopesticides,
some biological or low residue risk products can potentially be integrated into
programmes to reduce residue risk and these are worth considering especially when
disease pressure is not particularly high.
In a low downy mildew disease year consider extending the spray interval between
applications to reduce the overall number of sprays that may need to be applied to the
crop. Conversely, during high disease pressure periods consider reducing the spray
interval to maintain effective protection against key pathogens like downy mildew.
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In high disease pressure situations it would be inappropriate to use reduced dose rates
or biological products; certainly without significant further research to better understand
their range of protectant and/or curative activity.
Finally, prior to use of any pesticides always ensure you have a copy of the relevant
approval documents and that you have read and understood the requirements and
restrictions relating to their use. This is essential to provide adequate protection of
spray operators, the crop, consumers and the environment more broadly.
Agriculture and Horticulture Development Board 2023. All rights reserved 13
SCIENCE SECTION
Introduction
Lettuce (Lactuca sativa) is the most widely grown outdoor salad crop in the UK with a
production area of 6,043 ha for all types of lettuce, with crisphead iceberg being the most
widely grown type. In 2014, 140,500 tonnes of lettuce were produced at an estimated value
of £140.3 million (Defra Horticultural Statistics).
Downy mildew (Bremia lactucae) is a major and potentially devastating disease in both
protected and outdoor lettuce, particularly so in iceberg varieties, especially when
favourable wet, cool, humid conditions prevail. If not prevented or controlled from spreading
then whole crops can become unmarketable if the disease reaches the head of the lettuce.
Where whole fields are lost or ploughed-in due to severe outbreaks of the disease then
losses can reach into hundreds of thousands of pounds. A hectare of outdoor lettuce can be
worth up to £65,000 (Defra Horticultural Statistics 2014).
Other diseases are also important and contribute to significant losses in some crops. Grey
mould (Botrytis cinerea) is very often present on the oldest leaves and is usually removed
during the normal harvest trimming. Occasionally Botrytis causes plant losses in young
plants or severe basal rots when there are problems at plant establishment. Sclerotinia
sclerotiorum and Sclerotinia minor cause severe head rots near maturity. Bottom rot
caused by Rhizoctonia solani is more prevalent on protected crops than in field lettuce.
Ring spot (Microdochium panattonianum) is easily overlooked and can affect patches in
field and protected crops given prolonged wet conditions as it is a splash-borne pathogen.
In glasshouse crops ring spot is occasionally found in wetter parts of the crop e.g. under
leaky gutters.
Even low levels of disease can reduce marketable yield as infected leaves will require extra
trimming, so reducing head weight and marketability. A small blemish on the head can still
result in rejection or reduce its value, as the product is marketed in its fresh state and
retailer protocols have stringent quality regulations to be met.
This project aimed to evaluate the activity of new disease control programmes involving
conventional chemical fungicide and biological fungicides for control of the broad spectrum
of pathogens that occur in lettuce crops. The best combinations of treatments for control of
the various pathogens were investigated, whilst diversifying programmes to reduce the risks
of unacceptable residues at harvest and to minimise the chance of selection of fungicide
resistant strains.
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Project aim(s)To carry out an evaluation of the broader efficacy of various approved and novel fungicides
and bio-pesticides on both protected and outdoor lettuce in order to formulate a series of
disease control programmes and strategies for the control of the most important pathogens
of lettuce e.g. Bremia lactucae, Botrytis cinerea, Rhizoctonia solani and Sclerotinia
sclerotiorum and any other incidental pathogens that occurred at the selected trial sites.
Project objective(s):1. To conduct in vitro & in vivo (in planta) studies to screen new experimental products for
the control of Sclerotinia, Botrytis, Rhizoctonia & Oomycetes. Select those most
effective for in vivo screening in replicated field & glasshouse trials.
2. To carry out replicated trials in both field and glasshouse lettuce to a) evaluate the
activity of the short-listed novel products against the primary pathogen targets and b) to
compare a range of integrated fungicide/bio-control programmes designed to investigate
and optimise their broader efficacy and crop safety.
3. To validate the integrated programmes not only in terms of efficacy and crop safety but
also with respect to residue levels through a series of multi-residue analyses at harvest
to ensure retailer and consumer acceptance of the optimised programmes.
4. Prepare Annual & Final Reports, including AHDB Horticulture articles and an updated
Factsheet to effectively communicate new knowledge to the industry
The Annual report in 2013 covered in vitro screening and four 2012-2013 outdoor and
protected trials. The Annual report in 2014 covered the outdoor trial carried out from August
to October 2013 and protected trial on Sclerotinia minor done in March 2014. This final
report provides an overview and summary of earlier trials but also details the outdoor trials
carried out in Kent from August to October 2014 and August to October 2015 and the
protected trials carried out from August to September 2014 and September to November
2015.
(Grower Summary) gives the type, location and dates of experiments conducted within this
project.
Agriculture and Horticulture Development Board 2023. All rights reserved 15
Materials and methods
Autumn 2014 Field Trial
Kent, August to October 2014
Programme design
Programmes were designed taking into account requirements for the maximum number of
permitted applications, harvest intervals, diversification of different active ingredients and
the spectrum of diseases expected given the crop timing. Typically fungicides are applied
every 7–10 days commercially to maintain protection against downy mildew. All the
fungicides are used as protectants. Some have known problems with pesticide residues in
produce if applied too late in the programme, e.g. dithiocarbamates such as mancozeb.
Although these are very effective, and as multisite inhibitors useful as part of an anti-
resistant strategy, they often have long harvest intervals to minimise the residue risk and
therefore they are best used early in the programme to give good early protection with lower
residue risk. In autumn 2014 early programme products were also tested at half rate to
potentially reduce residue risk further and allow efficacy to be compared with similar full rate
treatments to assess the viability of this approach. Later programme applications were
made using different actives with action against downy mildew to maintain protection. As
well as varying the chemical groups used within programmes to guard against fungicide
resistance (utilising the FRAC codes, given in Table 2), where single actives were used that
have a high resistance risk, e.g. strobilurins such as azoxystrobin, they were used in
combination as a tank mix ensuring that the conditions on each product label could still be
met e.g. rates of application, harvest intervals and conditions of application.
Fungicides with activity against Botrytis and Sclerotinia were inserted early in treatment
programmes because the highest risk of infection from these pathogens is from damage at
planting. Botrytis is an opportunist secondary pathogen which will quickly colonise any
damaged or wilting tissues. Young leaves need to be protected from the spread of
Sclerotinia rot resulting from either mycelial or ascospore infection of senescing older
leaves. The ascospores arise from apothecia of Sclerotinia sclerotiorum developing from
sclerotia in the soil either in the lettuce crop or other nearby susceptible crops e.g. oilseed
rape and as the lettuce matures it becomes more difficult to effectively target the older
leaves.
Programmes of five timings in outdoor lettuce in autumn 2013 which included various
alternations with Amistar (azoxystrobin), Fubol Gold (mancozeb + metalaxyl-M), Karamate
(mancozeb), Previcur Energy (fosetyl-aluminium + propamocarb hydrochloride), Revus
Agriculture and Horticulture Development Board 2023. All rights reserved 16
(mandipropamid), HDC 145, F150 and F151 were particularly effective against downy
mildew and gave moderate control of Botrytis. The programme with tank mixes of Revus
and HDC F147 gave good downy mildew control. In autumn 2014 further experimental
programmes were designed taking forward the products used in the best programmes from
2013. Some new experimental products (HDC F149, F151 and F189) were included based
on efficacy information including that from the HortLink SCEPTRE Project CP 77.
Treatment list
Details on the products selected for use are given in Table 2. Their integration into
programmes designed using the principles described above are shown in Table 3.
Table 2. Products used on outdoor lettuce in autumn 2014, Kent, with active ingredients and full dose rates of products with use permitted on the crop on or off label
Product Active ingredients Full dose rate FRAC Code
Amistar azoxystrobin 1.0 L/ha 11
Fubol Gold mancozeb + metalaxyl-M 1.9 L/ha M3 + 4
HortiPhyte phosphite 2.0 L/ha foliar fertiliser
Infinito fluopicolide + propamocarb hydrochloride 1.6 L/ha 43 + 28
Invader dimethomorph + mancozeb 2.0 L/ha 40 + M3
Karamate mancozeb 2.0 kg/ha M3
Paraat dimethomorph 0.36 kg/ha 40
Previcur Energy
fosetyl-aluminium + propamocarb hydrochloride 1.25 L/ha 33 + 28
Revus mandipropamid 0.6 L/ha 40
Signum boscalid + pyraclostrobin 1.5 kg/ha 7 + 11
Silwet L-77 trisiloxane organosilicone copolymers 0.05% adjuvant
SL567A metalaxyl-M 0.16 L/ha 4
Switch cyprodinil + fludioxonil 0.8 kg/ha 9 + 12
HDC F145 (experimental biological product) - -
HDC F146 (conventional chemical) - -
HDC F147 (experimental product) - -
HDC F149 (conventional chemical) - -
HDC F150 (conventional chemical) - -
HDC F151 (conventional chemical) - -
HDC F188 (experimental biological product) - -
HDC F189 (experimental product) - -
Agriculture and Horticulture Development Board 2023. All rights reserved 17
Table 3. Fungicide programmes and treatment timings (T1 to T5) applied in the autumn 2014 outdoor lettuce trial, Kent. Products were applied at full manufacturer recommended rate unless otherwise stated
Target treatment application timings
Treat-ment
number
T15-7 days
post-transplant
T27 days after
T1T3
7days after T2T4
7 days after T3
T57days after T4
1 Untreated Untreated Untreated Untreated Untreated
2 Amistar + Karamate
Signum +Invader Infinito Revus -
3 Amistar + Karamate
Signum +Invader Infinito Fubol Gold Revus
4 Amistar + Karamate
Signum +Invader Infinito Revus HDC F145
5 Amistar + Karamate
Signum +Invader Infinito Revus HDC F188 +
Silwet L-77
6 HDC F189 Signum +Invader
HDC F189 + HortiPhyte Infinito Revus
7 HDC F150Previcur
Energy + HDC F151
Infinito Revus -
8 Switch + Paraat
Amistar +HDC F147
SL567A + HDC F147
Revus + HDC F147 -
9 Switch + Karamate
Amistar +Invader Fubol Gold Revus -
10 Amistar + Karamate Signum Infinito Paraat -
11 HDC F146 Infinito HDC F146 Revus -
12 0.5N Signum + 0.5N Rovral
0.5N Signum +0.5N Rovral +
InvaderInfinito Fubol Gold Revus
13 0.5N Switch + Karamate
0.5N HDC F151 + Invader
Previcur Energy Infinito Revus
14 0.5N Switch + Karamate
0.5N Signum + Invader Infinito Fubol Gold Revus
15 HDC F149 HDC F149 HDC F149 HDC F149 -
Trial design
The 14 treatment programmes were set out in comparison with a double untreated control
in a randomised block design replicated four times to give a total of 64 plots. Each plot
consisted of a 5m length of bed to give at least 60 lettuces per plot. Each bed was 1.8
metres wide with four rows of lettuce. The trial was carried out within a commercial lettuce
crop belonging to L.J. Betts, Church Farm, Church Road, Offham, Kent, with a variety
susceptible to downy mildew (cv. Etude) (Figure 1). Pathogen infection was by natural
occurrence.
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Figure 1. Overview of lettuce trial area at L.J. Betts in Kent, 2014.
Treatment applications
Treatments at all timings were applied with an Oxford precision knapsack sprayer with a 2
m boom using a fine – medium spray using an 02F110 nozzle at 2.5 bar pressure.
Products were applied at 200 L/ha for the first two timings while the crop was small, except
for HDC F189 at the recommendation of the supplying company. This product and all
products at the subsequent two or three timings per treatment were applied at 400 L/ha.
Assessments
The plots were assessed at each spray timing and at harvest for incidence and severity of
any of the target pathogens under investigation, and for crop phytotoxicity. Downy mildew
was observed after the third treatment application (04/09/2014) and Botrytis and Sclerotinia
were observed at the harvest assessment. Details of assessment methodology by disease
is below:
Overview
In all assessments, 20 plants per plot were assessed
Downy mildew
Downy mildew was scored % severity per plant unless disease was low in which case a
whole plot score was record as percentage severity of the plot affected.
Botrytis cinerea
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Each plant was scored according to the category scale below:
0 = no attack;
1 = slight attack, infection of basal petioles only;
2 = moderate attack, stem lesion not girdling stem;
3 = heavy/severe attack, stem lesion girdling stem, or upper leaves infected, lettuce
unmarketable (including plants completely destroyed by Botrytis during the trial).
4 = total plant collapse/dead
Sclerotinia spp.
Each plant was scored according to the category scale below:
0 = no attack;
1 = slight attack, plant wilted, mycelium of Sclerotinia spp. present on lower leaves
2 = moderate attack, infection of upper leaves
3 = heavy/severe attack,
4 = total plant collapse/dead
Both the Botrytis and the Sclerotinia category scales were converted to a 0-100 index score
for severity using the following formula:
([CAT 1*] + [CAT 2* X 2] + [CAT 3* X 3] + [CAT 4* X 4] X 100
NO. HEADS ASSESSED 4 (no. of assessment categories)
* Number of heads in each of the four categories
A measure of yield was taken at harvest by using the marketable weight of 20 trimmed
heads of lettuce per plot. The heads which were used for the marketable yield calculation
were trimmed so all diseased leaves were removed. If disease symptoms were present on
the head or was too severe for trimming then they were removed and classed as
unmarketable.
Pesticide residue analysis
Samples were taken 13 days after Timing 5 sprays (13 days before the final harvest) for
residue testing. Three untrimmed heads were taken from each treatment replicate of each
treatment programme. The heads from replicates one and two were combined as one
sample and material from replicates three and four as another.
Not all treatments were sent for analysis; particularly where the last two application timings
used the same products. Samples from eight treatments, plus from untreated plots, were
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sent for residue analysis. Plots where dithiocarbamates or fosetyl-Al had been applied were
also specifically analysed for these materials in addition to the standard analyses.
The retail guideline is for no residues to be more than 25% of the MRL, but the goal of this
project was to record no more than 10% of MRL or less.
Statistical Analyses
The data for the outdoor trials were analysed by ANOVA using a Genstat statistical software
package.
As this trial contained a double untreated control (Treatment 1 had 8 replicates), the
ANOVA was unbalanced and required a separate least significant difference (LSD) value
when comparing different sets of treatments. For comparing the untreated (treatment 1)
with the fungicide treatments, the max-min figure should be used. For comparing between
the fungicide treatments (Treatments 2-15) the min.rep figure should be used.
Autumn 2015 Field Trial
Lincolnshire, July to September 2015
Treatment list design
Historically in this project the outdoor field trials have been focused on developing
programmes designed taking into account requirements on the maximum number of
permitted applications, harvest intervals, diversification of different active ingredients and
the spectrum of diseases expected. For the final outdoor lettuce trial in 2015 products were
not applied in programmes, instead repeat applications being made of the same treatment
at five spray intervals. In total eight products were investigated with each applied at full and
half rate at each spray timing to evaluate this practise for potentially reducing residue risk
and allow efficacy to be compared with similar full rate treatments to assess the viability of
this approach.
Treatment list
Details on the products selected for use are given in Table 4.
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Table 4. Products used on outdoor lettuce in autumn 2015, Lincolnshire, with active ingredients, full and half dose rates of products investigated and FRAC code.Treatmen
t no. Treatment Kg or L/Ha Active ingredient FRAC
Code1 Untreated -
- -2 Untreated -
3 Fubol Gold 1.9mancozeb + metalaxyl-M M3 + 4
4 Fubol Gold 0.95
5 Invader 2dimethomorph + mancozeb 40 + M3
6 Invader 1
7 Revus 0.6mandipropamid 40
8 Revus 0.3
9 Infinito 1.6 fluopicolide + propamocarb hydrochloride 43 + 28
10 Infinito 0.8
11 Previcur Energy 2.5 fosetyl-aluminium + propamocarb hydrochloride 33 + 28
12 Previcur Energy 1.25
13 Amistar 1azoxystrobin 11
14 Amistar 0.5
15 Fenomenal* 2.5 Fenamidone + fosetyl-aluminium 33 + 11
16 Fenomenal 1.25
17 F145 2.5 Experimental biological control stimulant
18 F145 + Revus 2.5 + 0.3 Experimental biological control + mandipropamid
stimulant + 40
* Fenomenal EAMU to be revoked at the end of July 2016, not approved for use after this date.
Fubol Gold was selected as the standard product to be used to compare the performance of
the other products and also allow for changes in product efficacy to be monitored compared
to previous years. Infinito was selected as it is a newer product currently favoured by
growers. Revus was selected as it has provided high levels of efficacy in previous years of
this project and is a product favoured by growers though its efficacy at half rate is unknown.
Amistar and Invader were selected as they have provided steady performance in all lettuce
trials but as they are usually at the start of fungicide programmes it has been difficult to
identify these products’ effect on late downy mildew epidemics.
Previcur Energy was selected as it was effective in protected trials but as it has previously
been tested at early stages in fungicide programmes little data has been generated on the
product’s efficacy outdoor on late epidemics.
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Fenomenal was selected, because it already has off-label authorisation against downy
mildew (in ornamental plants and wine grapes), and the company marketing it was willing
for it to be tested on the outdoor lettuce with the potential for Extension of Authorisation for
Minor Use to then be sought1. F145 is a biofungicide and was selected as it was used in a
tank mix during 2013 with Revus, so it was difficult to quantify how much additional efficacy
F145 was providing. Therefore it was included so that this product’s individual performance
could be quantified. This product produced some interesting results in SCEPTRE, and as
such it was also mixed with half rate Revus in Treatment 18.
Trial design
The 18 treatment programmes were set out in comparison with a double untreated control
in a randomised block design replicated four times to give a total of 72 plots. Each plot
consisted of a 5m length of bed to give at least 60 lettuces per plot. Each bed was 1.8
metres wide with five rows of lettuce (Figure 2).
The trial was carried out within a
commercial lettuce crop belonging to J E
Piccaver & Co, Norfolk House Farm,
Gedney Marsh, Spalding, Lincolnshire
PE12 9PB, with a variety susceptible to
downy mildew. Pathogen infection was by
natural occurrence.
Treatment applications
Treatments at all timings were applied with
an Oxford precision knapsack sprayer with
a 1.5 m boom using a medium spray at 2
bar pressure. Products were applied at 200
L/ha for the first two timings whilst the crop
was small and all products at the
subsequent three timings were applied at
400 L/ha.
Assessments
1 Fenomenal was granted an EAMU, however this was in error and has been revoked. It will not be approved for use after the end of July 2016.
Agriculture and Horticulture Development Board 2023. All rights reserved 23
Figure 2. Overview of lettuce trial area at Piccaver’s in Lincolnshire, 2015.
The plots were assessed at each spray timing and at harvest for incidence and severity of
the target pathogen downy mildew and also for any non-target disease as well as crop
phytotoxicity. Details of assessment methodology by disease is outlined below:
Overview
In all assessments, 20 plants per plot were assessed.
Downy mildew
Downy mildew would have been scored as % severity per plant unless disease was low in
which case a whole plot score would have been recorded as percentage severity of the plot
affected.
Botrytis cinerea
Each plant was scored according to the category scale below:
0 = no attack;
1 = slight attack, infection of basal petioles only;
2 = moderate attack, stem lesion not girdling stem;
3 = heavy/severe attack, stem lesion girdling stem, or upper leaves infected, lettuce
unmarketable (including plants completely destroyed by Botrytis during the trial).
4 = total plant collapse/dead
Sclerotinia spp.
Each plant was scored according to the category scale below:
0 = no attack;
1 = slight attack, plant wilted, mycelium of Sclerotinia spp. present on lower leaves
2 = moderate attack, infection of upper leaves
3 = heavy/severe attack,
4 = total plant collapse/dead
Both the Botrytis and the Sclerotinia category scales were then converted to a 0-100 index
score for severity using the following formula:
([CAT 1*] + [CAT 2* X 2] + [CAT 3* X 3] + [CAT 4* X 4] X 100
NO. HEADS ASSESSED 4
* Number of heads in each of the four categories
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A measure of yield was taken at harvest by using the marketable weight of 20 trimmed
heads of lettuce per plot. The heads which were used for the marketable yield calculation
were trimmed so all diseased leaves were removed. If disease symptoms were present on
the head or was too severe for trimming then they were removed and classed as
unmarketable (Figure 3).
Figure 3. Unmarketable head, showing necrosis caused by Botrytis.
Statistical Analyses
The data for the outdoor trials were analysed by ANOVA using a Genstat statistical software
package.
Autumn 2014 Protected Trial, STC
July-Sept 2014
Programme design
In this trial there were 12 treatment programmes at four application timings. The treatments
included an untreated, an industry standard, four commercial programmes, three
experimental commercial programmes (products applied at half rates and/or in tank mixes),
and three experimental programmes (novel products and products not yet approved on
lettuce) (Table 5). The programmes were focused on providing broad spectrum control of
the various pathogens with particular attention to downy mildew which is more prevalent in
the autumn.
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Table 5. Fungicide programmes in the autumn protected trial, Yorkshire 2014
Application Timing
Treatment T1 T2 T3 T4
Type Pre-planting 2-3 days post-planting
10-14 Days after T1
10-14 Days after T2
10-14 Days after T3
Date 07/08/2014 12/08/2014 22/08/2014 01/09/2014 10/09/2014
1 No application Untreated Untreated Untreated Untreated
Commercial programmes
2 No application Amistar Fubol Gold Switch Revus
3 Contans Amistar Fubol Gold Paraat Switch
4 Contans Revus Amistar Switch Revus
5 Contans Amistar Paraat HDC F145 Serenade
6 No application Fubol Gold Switch Signum Revus
Experimental commercial programmes
7 No application 0.5N Amistar + 0.5N Fubol Gold
0.5N Signum + 0.5N Switch
0.5N Paraat + 0.5N Octave
0.5N Revus + 1N Serenade
8 No application 0.5N Signum + 0.5N Fubol Gold
0.5N Paraat + 0.5N Octave
0.5N Amistar + 0.5N Revus
-
9 No application 0.5N Signum + 0.5N Fubol Gold
- 0.5N Switch + 0.5N Revus
-
Experimental programmes
10 No application 1N HDC F187 0.5N Amistar + 0.5N Fubol Gold
0.5N HDC F152 + 0.5N Revus
1N HDC F145
11 No application 0.5N HDC F153 + 0.5N Signum
1N HDC F159 0.5N HDC F153 + 0.5N Signum
1N Serenade
12 No application 1N HDC F151 0.5N Infinito + 0.5N HDC F150
0.5N HDC F151 + 0.5N HDC F150
1N Serenade
Trial design
The 12 treatment programmes above were set out in a randomised complete block design
replicated four times to give a total of 48 plots. Each plot was 1 metre wide and 1.2 metres
long and was planted with 42 lettuces, of which 20 were assessed. To increase the
chances of infection by the target pathogens, the trial was undertaken in a glasshouse
which had been used in the past for lettuce disease trials and it was known to have high
levels of fungal pathogens, especially Sclerotinia and Rhizoctonia, already present in the
soil. The likelihood of infection was increased by carrying out the trial in autumn when
conditions are usually favourable for downy mildew. No inoculation was necessary as
Bremia lactucae and Botrytis cinerea infected the crop naturally.
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Treatment applications
Treatments at all timings were applied with an Oxford precision knapsack sprayer with a 2
m boom using a fine – medium spray at 2 bar pressure with the number of nozzles reduced
to account for the plot width. All applications were applied at a water rate of 200 l/ha with
01F110 flat fan nozzles.
Assessments
The plots were assessed three times for incidence and severity of each disease and crop
safety. Severity was scored per plant on a 0-3 scale where 0 = no disease, 1 = low disease
level, 2 = moderate disease level and 3 = high disease level.
Table 6. Crop diary for autumn 2014 trial.
Date Action
16/07/2014 Lettuce cv Cobham Green sown
07/08/2014 Contans applied
08/08/2014 Crop planted & sclerotia introduced
12/08/2014 1st treatment application
22/08/2014 2nd treatment application. Phytotoxicity assessment: none
01/09/2014 3rd treatment application. Downy mildew and Rhizoctonia infection observed.
02/09/2014 1st detailed assessment. Phytotoxicity assessment: T11
10/09/2014 4th treatment application
12/09/2014 2nd detailed assessment. Phytotoxicity assessment: none
22/09/2014 3rd detailed assessment. Phytotoxicity assessment: none
22/09/2014 Harvest (there were insufficient heads at harvest for residues analyses due to high levels of Sclerotinia and Rhizoctonia).
Statistical Analyses
The data for the indoor trials were analysed by Analysis of Variance (ANOVA) using ARM 9
statistical software package (Gylling Data Management Inc.).
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Autumn 2015 Protected Trial, STC
Sept-November 2015
Programme design
In this trial there were 12 treatment programmes at four application timings. The treatments
included an untreated, an industry standard, a commercial programme, three experimental
commercial programmes (products applied at half rates and/or in tank mixes), three
experimental commercial 2 spray programmes, and four experimental programmes (novel
products and products not yet approved on lettuce) (Table 7). The programmes were
focused on providing control of downy mildew which is more prevalent in the autumn.
Table 7. Fungicide programmes in the autumn protected trial, Yorkshire 2015
Application Timing
Treatment T1 T2 T3 T4
Type 6 days post-planting
7 Days after T1 13 Days after T2 28 Days after T3
Date 10/09/2014 17/09/2015 30/09/2015 28/10/2015
1 Untreated Untreated Untreated Untreated
Commercial programme
2 1N Amistar 1N Fubol Gold 1N Paraat 1N Serenade
Experimental commercial programmes
3 0.5N Amistar 0.5N Fubol Gold 0.5N Paraat 1N Serenade
4 0.5N Amistar + 0.5N Fubol Gold
1N Paraat 1N Revus -
5 0.5N Amistar + 0.5N Fubol Gold
0.5N Paraat 0.5N Revus -
Experimental commercial 2 spray programmes
6 0.5N Amistar + 0.5N Fubol Gold
- 0.5N Paraat +0.5N Revus
-
7 1N Paraat - 1N Revus -
8 0.5N Paraat - 0.5N Revus -
Experimental programmes
9 1N F150 1N Previcur Energy 1N Infinito 1N Serenade
10 0.5N F150 0.5N Previcur Energy
0.5N Infinito 1N Serenade
11 1N F146 1N Invader 1N F153 1N Serenade
12 0.5N F146 0.5N Invader 0.5N F153 1N Serenade
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Trial design
The 12 treatment programmes above were set out in a randomised complete block design
replicated four times to give a total of 48 plots. Each plot was 1 metre wide and 1.2 metres
long and was planted with 21 lettuces of the variety Cobham Green, which is universally
susceptible to downy mildew, and 21 lettuces of the commercial variety Brian, making a
total of 42 lettuces, of which 20 were assessed (10 of Cobham Green and 10 of Brian). To
increase the chances of infection by the target pathogens, six plants per plot (three Cobham
Green and three Brian) were inoculated twice with a spore suspension of Bremia lactucae:
the first time following the second treatment application using a spore suspension prepared
from frozen infected leaf material; the second time following the third treatment application
using a spore suspension prepared from fresh infected leaf material. The likelihood of
infection was increased by carrying out the trial in autumn when conditions are usually
favourable for downy mildew.
Treatment applications
Treatments at all timings were applied with an Oxford precision knapsack sprayer with a 2
m boom using a fine – medium spray at 2 bar pressure with nozzle number reduced to
account for the plot width. Applications were applied at a water rate of 500 l/ha (first
application) decreasing to 200 l/ha (fourth application) with 01F110 flat fan nozzles.
Table 8. Crop diary for autumn 2015 trial.
Date Action
12/08/2015 Lettuce cv Cobham Green sown
14/08/2015 Lettuce cv Brian sown
03/09/2015 Lettuce cv Cobham Green planted
04/09/2015 Lettuce cv Brian planted
10/09/2015 1st treatment application
17/09/2015 2nd treatment application. Phytotoxicity assessment: none
20/09/2015 Trial inoculated with spore suspension of Bremia lactucae prepared from frozen infected plant material. Phytotoxicity assessment: none
30/09/2015 3rd treatment application.
05/10/2015 Trial inoculated with spore suspension of Bremia lactucae prepared from fresh infected plant material. Phytotoxicity assessment: none
27/10/2015 1st detailed assessment.
28/10/2015 4th treatment application
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04/11/2015 2nd detailed assessment. Phytotoxicity assessment: none
10/11/2015 3rd detailed assessment.
11/11/2015 Harvest
Assessments
The plots were assessed three times for incidence and severity of each disease and crop
safety. Severity was scored per plant on a 0-3 scale where 0 = no disease, 1 = low disease
level, 2 = moderate disease level and 3 = high disease level.
Statistical Analyses
The data for the indoor trials were analysed by Analysis of Variance (ANOVA) using ARM 9
statistical software package (Gylling Data Management Inc.).
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Results and Discussion
Outdoor Trials
Autumn 2014
Overview
The sprays and assessments were conducted according to the schedule included in Table 9
below. Downy mildew levels in this year’s outdoor lettuce trial were low. No diseases were
observed in the first assessment on 14 August 2014 at T1 and only trace levels were
observed in some plots during the assessments on the 21, 27 August and 4 September at
T2, T3 and T4. At the T5 disease assessment on 11 September disease levels were still
low. Downy mildew incidence was 2.5% in untreated plots with an average disease
severity of 0.1% leaf area affected, with no significant treatment effects observed (F pr
0.891).
Table 9. Timing of sprays and assessments on outdoor lettuce trial, autumn 2014, Kent.
DateSpray timing
sAssessment carried out
14/08/2014 T1 Disease
21/08/2014 T2 Disease and Phytotoxicity
27/08/2014 T3 Disease and Phytotoxicity
04/09/2014 T4 Disease and Phytotoxicity
11/09/2014 T5 Disease and Phytotoxicity
18/09/2014 - Disease and Phytotoxicity
24/09/2014 - Disease and Residue
06/10/2014 - Disease, Marketability and Yield
At the T5 + 7 days assessment on 18 September all treatments were found to have a
significantly lower incidence of downy mildew (0.00 – 1.25%) compared with the untreated
control (6.25%), although there were no significant differences between treatments. At the
24 September assessment (13 days post timing 5 application), downy mildew incidence had
increased to 16.3% of plants in the untreated control, significantly higher than the treated
plots (0.0 – 1.3% incidence) although there were no treatment differences. At harvest (24
days after T5), downy mildew incidence had increased to 90% (% of plants affected), with a
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downy mildew severity score of 7% severity (% leaf area affected) in the untreated plots.
No phytotoxicity was observed within this trial. Disease progress is shown in Figure 4.
8/29/2014 9/3/2014 9/8/2014 9/13/2014 9/18/2014 9/23/2014 9/28/2014 10/3/2014 10/8/20140
1
2
3
4
5
6
7
8
0.01 0.01 0.13 0.29
7.21
Date
Dow
ny m
ildew
seve
rity
(% le
af a
rea
af-
fect
ed)
Figure 4. Progress of downy mildew in untreated lettuce plots, autumn 2014, Kent.
Downy mildew
The final disease assessment was completed on 6 October 2014, 4 weeks after the Timing
5 fungicide applications. At this assessment downy mildew incidence and severity had
increased considerably from the 24 September assessment. Eleven fungicide treatment
programmes (18.8 – 56.2% incidence) provided significant control of downy mildew
compared with the untreated (90% incidence). The most effective treatment was Treatment
8 which comprised the alternating sequence of tank mixes of Switch (cyprodinil +
fludioxonil) + Paraat (dimethomorph)/Amistar (azoxystrobin) + HDC F147/SL567A
(metalaxyl-M) + HDC F147/Revus (mandipropamid) + HDC F147 with a disease incidence
of 18.8% (Figure 5, Table 10).
Treatment 9 and Treatment 8 were comparable treatments. Treatment 9 contained
mancozeb based treatments throughout much of the programme, whereas Treatment 8
utilised other actives in either Paraat or the experimental biological HDC F147 instead of
mancozeb. Results showed that the disease incidence for the treatment without the
mancozeb based products had lower downy mildew levels (18.8% incidence) than
Treatment 9 which contained mancozeb based treatments (56.2%). However differences
between the two programmes were not quite significant. It is important to also consider
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modes of action of actives and relative timings of application. Mancozeb is a multi-site
protectant product and needs to be applied every few days to protect new growth.
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Table 10. Lettuce downy mildew incidence and severity at the harvest assessment, Kent, 6 October 2014.
Treatment number
T1 5-7 days post transplanting
T2 7 days after T1 T3 -7days after T2 T4 7 days after T3
T5 7days after T4
Incidence (% of plants
affected)
Severity (% leaf
area affected)
1 Untreated Untreated Untreated Untreated Untreated 90.0 7.22 Amistar + Karamate Signum + Invader Infinito Revus - 27.5 0.33 Amistar + Karamate Signum + Invader Infinito Fubol Gold Revus 26.2 0.34 Amistar + Karamate Signum + Invader Infinito Revus HDC F145 27.5 0.25 Amistar + Karamate Signum + Invader Infinito Revus HDC F188
+ Silwet L-77
52.5 1.6
6 HDC F189 Signum + Invader HDC F189 + HortiPhyte
Infinito Revus 45.0 0.8
7 HDC F150 PrevicurEnergy + HDC F151
Infinito Revus - 65.0 1.8
8 Switch + Paraat Amistar + HDC F147 SL567A + HDC F147
Revus + HDC F147
- 18.8 0.2
9 Switch + Karamate Amistar + Invader Fubol Gold Revus - 56.2 1.410 Amistar + Karamate Signum Infinito Paraat - 67.5 3.011 HDC F146 Infinito HDC F146 Revus - 70.0 2.712 0.5N Signum + 0.5N
Rovral0.5N Signum + 0.5N
Rovral + InvaderInfinito Fubol Gold Revus 38.8 0.8
13 0.5N Switch + Karamate
0.5N HDC F151 + Invader PrevicurEnergy Infinito Revus 38.8 0.4
14 0.5N Switch + Karamate
0.5N Signum + Invader Infinito Fubol Gold Revus 35.0 0.7
15 HDC F149 HDC F149 HDC F149 HDC F149 - 67.5 0.9Fpr 0.002 <0.001SED min.rep 18.84 1.80
max-min 16.31 1.55LSD min.rep 37.92 3.61
max-min 32.84 3.13
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LSD
Treatments 2, 3, 4 and 5 demonstrate the effect of product positioning and timing at the end
of fungicide programmes (Timings 4 and 5) (Table 11). The standard programme,
Treatment 2, was found to have a downy mildew incidence of 27.5%. When an alternative
spray was added to this standard programme at spray Timing 4, and the Revus application
delayed until spray Timing 5, downy mildew incidence was not reduced. Similarly, when
comparing treatments 4 and 5 to the standard four-spray programme (Treatment 2), it was
found that the addition of the biofungicide HDC F145 did not improve control, and the
addition of the biofungicide HDC F188 and the adjuvant Silwet L-77 actually appeared to
decrease the level of control, with a disease incidence of 52.5%. It is important to note that
the difference in disease incidence between treatment 2 and treatment 5 was not
statistically significant.
Table 11. Products used in Treatments 2 to 5 before and after the third application timing.
Treatment Timing 1 Timing 2 Timing 3 Timing 4 Timing 5 Downy mildew
incidence %
2
Amistar + Karamate
Signum + Invader Infinito
Revus - 27.50
3 Fubol Gold Revus 26.20
4 Revus HDC F145 27.50
Agriculture and Horticulture Development Board 2023. All rights reserved 35
Unt
reat
ed -
Revu
s
HD
C F1
45
HD
C F1
88 +
Silw
et L
-77
Revu
s - - - - -
Revu
s
Revu
s
Revu
s -
Untreated Revus Fubol Gold
Revus Revus Infinito Revus Revus + HDC F147
Revus Paraat Revus Fubol Gold
Infinito Fubol Gold
HDC F149
Untreated Infinito Infinito Infinito Infinito HDC F189 + Horti-Phyte
Infinito SL567A + HDC F147
Fubol Gold
Infinito HDC F146 Infinito Previ-curEnergy
Infinito HDC F149
Untreated Signum + Invader
Signum + Invader
Signum + Invader
Signum + Invader
Signum + Invader
Previ-curEnergy
+ HDC F151
Amistar + HDC F147
Amistar + Invader
Signum Infinito 0.5N Signum +
0.5N Rovral + Invader
0.5N HDC F151 + Invader
0.5N Signum + Invader
HDC F149
Untreated Amistar + Karamate
Amistar + Karamate
Amistar + Karamate
Amistar + Karamate
HDC F189 HDC F150 Switch + Paraat
Switch + Karamate
Amistar + Karamate
HDC F146 0.5N Signum +
0.5N Rovral
0.5N Switch +
Karamate
0.5N Switch +
Karamate
HDC F149
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
0
10
20
30
40
50
60
70
80
90
100
Fungicide programme
Dow
ny m
ildew
incid
ence
(%)
5 Revus HDC F188 + Silwet L-77 52.50
Treatment 6 contained a programme which evaluated HDC F189 at Timing 1 and HDC
F189 + HortiPhyte at Timing 3 (with standard products applied at Timings 2, 4 and 5).
HDC F189 is a biofungicide which allowed the number of conventional fungicides to be
reduced and gave similar % cover to the conventional fungicide programmes.
Treatment 10 which contained Amistar + Karamate (mancozeb), Signum (boscalid +
pyraclostrobin), Infinito (fluopicolide + propamocarb hydrochloride) and Paraat was found to
have a significantly higher downy mildew incidence (67.5%) than the standard spray
programme (Treatment 2 with 27.5%). The main difference between Treatment 10 and the
standard programme was the use of Paraat rather than Revus as the final spray, with
disease incidence being significantly lower where Revus was applied at Timing 4.
Treatments 12, 13 and 14 used Signum, Rovral, HDC F151 and Switch at half rate at the T1
and T2 timings. Disease incidence for these treatments ranged from 35.0 – 38.8%,
therefore efficacy was not significantly reduced compared to the standard treatment
programme, treatment 2, where all products were applied at full label rate with a disease
incidence of 27.5%.
Treatment programmes 7, 11 and 15 tested a range of experimental fungicide products in
various programme positions. None of these programmes reduced downy mildew incidence
significantly compared with the untreated control, although all three programmes reduced
disease severity.
Botrytis and Sclerotinia
Botrytis was observed throughout the trial area however there were no significant treatment
effects on disease incidence (F pr 0.875) or severity (F pr 0.859). On average, 64% of
plants were affected by Botrytis, with an average severity index of 20 (based on a 0-100
range of increasing severity as the symptoms spread from basal to upper leaves) (Table
12).
Sclerotinia infection was also observed throughout the trial area at the harvest assessment
(Table13). Differences in Sclerotinia incidence between treatment programmes were near
significance (F pr 0.054), ranging from a mean 11% to 49% of plants affected, however
there were no consistent treatment trends. Sclerotinia severity was also assessed and
represented by the 0-100 index, with results ranging from 12.3 in the untreated to 4.1 in the
most effective treatment (treatment 10: Amistar + Karamate, Signum, Infinito, Paraat).
Agriculture and Horticulture Development Board 2023. All rights reserved 36
There was a trend for some treatments to have a higher Sclerotinia severity index score
than the untreated with treatments 9 and 11 having scores of 16.3 and 14.1 respectively. No
significant treatment effects were observed in regards to Sclerotinia severity scores (Fpr
0.081) (Table 13).
Yield
Marketable yield was assessed from 20 heads per plot sampled from a set area within the
central two rows. The total weight of marketable heads excluded any of the 20 heads that
were unmarketable. The percentage of the 20 heads per plot assessed which were
marketable was also assessed as well as the mean weight per marketable head. Head
weights were not significantly affected by treatments (Fpr 0.884), however there was a trend
for Treatment 10 to have the lowest mean weight per marketable head, with 570g per
marketable head on average compared to the range of weights per marketable head in the
trial which stretched from 570 to 670g/head. Percentage of marketable heads was also not
significantly affected by treatment (Fpr 0.227), with the percentage of heads making
marketable standard ranging from 95 to 100%. No phytotoxicity was seen (Table 14).
Residue data
Residue samples were collected 13 days after the Timing 5 treatments on 24 September
2014. Results from this analysis for the treatments sampled are shown in Table 15. No
active ingredient was found to exceed MRL in this experiment. The highest residue picked
up was dithiocarbamates in Treatment 3 where Fubol Gold was used at Timing 4, where
levels under 17% of MRL were detected, and under 7% in Treatment 9 where Fubol Gold
was last used at Timing 3. Timing 3 application was 28 days before residue samples were
taken. All other actives were detected at less than 5% MRL.
Agriculture and Horticulture Development Board 2023. All rights reserved 37
Table 12. Botrytis incidence and severity on lettuce at the harvest assessment, Kent, 6 October 2014.
Treatment number
T1 5-7 days post transplanting
T2 7 days after T1 T3 -7days after T2
T4 7 days after T3
T5 7days after T4 Incidence (% of plants
affected)
Severity (0-100 index)
1 Untreated Untreated Untreated Untreated Untreated 63.8 20.82 Amistar + Karamate Signum + Invader Infinito Revus - 65.0 19.73 Amistar + Karamate Signum + Invader Infinito Fubol Gold Revus 57.5 17.54 Amistar + Karamate Signum + Invader Infinito Revus HDC F145 68.8 20.65 Amistar + Karamate Signum + Invader Infinito Revus HDC F188 +
Silwet L-7758.8 16.3
6 HDC F189 Signum + Invader HDC F189 + HortiPhyte
Infinito Revus 58.8 18.4
7 HDC F150 Previcur Energy +HDC F151
Infinito Revus - 72.5 20.9
8 Switch + Paraat Amistar + HDC F147 SL567A + HDC F147
Revus + HDC F147
- 66.2 21.9
9 Switch + Karamate Amistar + Invader Fubol Gold Revus - 50.5 14.610 Amistar + Karamate Signum Infinito Paraat - 67.5 20.611 HDC F146 Infinito HDC F146 Revus - 66.2 20.912 0.5N Signum + 0.5N
Rovral0.5N Signum +
0.5N Rovral + InvaderInfinito Fubol Gold Revus 68.8 22.0
13 0.5N Switch + Karamate
0.5N HDC F151 + Invader Previcur Energy Infinito Revus 60.0 18.8
14 0.5N Switch + Karamate
0.5N Signum + Invader Infinito Fubol Gold Revus 75.0 24.1
15 HDC F149 HDC F149 HDC F149 HDC F149 - 66.2 20.6Fpr 0.875 (ns) 0.859 (ns)
SED min.rep 11.88 4.46max-min 10.29 3.86
LSD min.rep 23.92 8.98max-min 20.71 7.78
Agriculture and Horticulture Development Board 2023. All rights reserved 38
Table 13. Sclerotinia incidence and severity on lettuce at the harvest assessment for treatment programmes 1 to 5 showing products used, Kent, 6 October 2014.
Treatment number
T15-7 days post transplanting
T27 days after T1
T37days after T2
T47 days after T3
T57days after T4
Incidence (% of plants affected)
Severity (0-100 index)
1 Untreated Untreated Untreated Untreated Untreated 29.4 12.32 Amistar + Karamate Signum + Invader Infinito Revus - 36.2 12.23 Amistar + Karamate Signum + Invader Infinito Fubol Gold Revus 17.5 4.74 Amistar + Karamate Signum + Invader Infinito Revus HDC F145 20.0 6.95 Amistar + Karamate Signum + Invader Infinito Revus HDC F188 + Silwet
L-7722.5 7.8
6 HDC F189 Signum + Invader HDC F189 + HortiPhyte
Infinito Revus 25.0 6.9
7 HDC F150 Previcur Energy +HDC F151
Infinito Revus - 21.2 6.6
8 Switch + Paraat Amistar + HDC F147 SL567A + HDC F147
Revus + HDC F147
- 27.5 9.7
9 Switch + Karamate Amistar +Invader
Fubol Gold Revus - 48.8 16.3
10 Amistar + Karamate Signum Infinito Paraat - 11.2 4.111 HDC F146 Infinito HDC F146 Revus - 41.2 14.112 0.5N Signum +
0.5N Rovral0.5N Signum +
0.5N Rovral + InvaderInfinito Fubol Gold Revus 22.5 8.4
13 0.5N Switch + Karamate
0.5N HDC F151 +Invader
Previcur Energy Infinito Revus 21.2 8.1
14 0.5N Switch + Karamate
0.5N Signum +Invader
Infinito Fubol Gold Revus 15.0 4.4
15 HDC F149 HDC F149 HDC F149 HDC F149 - 18.8 5.9F pr 0.054 (ns) 0.081 (ns)
SED min.rep 4.08 4.46max-min 3.53 3.86
LSD min.rep 8.21 8.98max-min 7.11 7.78
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Table 14. Yield data at the harvest assessment, Kent, 6 October 2014 for the number of marketable heads out of 20 sampled per plot.Treatment
numberT1
5-7 days post transplanting
T27 days after T1
T37days after T2
T47 days after T3
T57days after T4
Total marketable head weight
(kg)
% market-
able heads
Mean market-
able head weight (g)
1 Untreated Untreated Untreated Untreated Untreated 13.16 98.8 6702 Amistar + Karamate Signum + Invader Infinito Revus - 12.08 96.3 630
3 Amistar + Karamate Signum + Invader Infinito Fubol Gold Revus 12.73 100.0 640
4 Amistar + Karamate Signum + Invader Infinito Revus HDC F145 12.28 98.8 620
5 Amistar + Karamate Signum + Invader Infinito Revus HDC F188 + Silwet L-77
12.03 98.8 610
6 HDC F189 Signum + Invader HDC F189 + HortiPhyte
Infinito Revus 12.83 97.5 660
7 HDC F150 Previcur Energy +HDC F151
Infinito Revus - 12.75 98.8 650
8 Switch + Paraat Amistar + HDC F147 SL567A + HDC F147 Revus + HDC F147 - 12.80 100.0 640
9 Switch + Karamate Amistar + Invader Fubol Gold Revus - 12.80 98.8 650
10 Amistar + Karamate Signum Infinito Paraat - 10.95 96.3 570
11 HDC F146 Infinito HDC F146 Revus - 12.80 100.0 640
12 0.5N Signum + 0.5N Rovral
0.5N Signum +0.5N Rovral +
Invader
Infinito Fubol Gold Revus 11.08 93.8 590
13 0.5N Switch + Karamate
0.5N HDC F151 + Invader
Previcur Energy Infinito Revus 12.88 97.5 660
14 0.5N Switch + Karamate
0.5N Signum +Invader
Infinito Fubol Gold Revus 13.18 100.0 660
15 HDC F149 HDC F149 HDC F149 HDC F149 - 12.13 95.0 630
Fpr 0.682 (ns) 0.227 (ns) 0.884 (ns)SED min.rep 1.128 2.39 54
max-min 0.976 2.07 46LSD min.rep 2.270 4.80 107
max-min 1.966 4.16 93
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Table 15. Residue data, expressed as percentage of MRL, Kent, from heads collected from selected treatments in 24 September 2014.
Residues - expressed as % of MRL
Trt no. BoscalidDimetho-
morph CyprodinilLambda
CyhalothrinMandi-
propamidPropamo-
carbDithio-
carbamatesAzoxy-strobin
Pyraclo-strobin Fluopicolide
1 0.0 0.0 0.0 1.0 0.0 0.0 0.0 0.0 0.0 0.02 0.2 0.0 0.0 2.0 0.7 0.2 0.7 0.0 0.0 0.03 0.1 0.0 0.0 2.0 1.9 0.2 16.8 0.0 0.0 0.07 0.0 0.0 0.0 3.0 0.5 0.2 3.2 0.0 0.0 0.08 0.1 0.0 0.0 2.0 0.3 0.1 0.0 0.0 0.0 0.09 0.0 0.1 0.0 2.0 0.5 0.0 6.9 0.1 0.0 0.0
10 0.1 0.2 0.0 3.0 0.2 0.2 0.0 0.0 0.0 0.011 0.0 0.0 0.0 3.0 0.7 0.1 1.6 0.0 1.5 0.013 0.0 0.0 0.0 2.0 1.1 1.2 0.0 0.0 0.0 0.3
2014 MRL
(mg/kg)30.0 15.0 15.0 0.5 25.0 50.0 5.0 15.0 2.0 9.0
*Fosetyl-aluminium: No residue detected above the limit of detection.
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Autumn 2015
Overview
The sprays and assessments were conducted according to the schedule included in Table
16 below. Downy mildew did not develop in the 2015 outdoor lettuce trial. No diseases
were observed in the first assessment on 30 July 2015 at T1, nor was any disease
observed on 6 August, 13 August, 20 August, and 27 August. Low levels of Botrytis and
Sclerotinia were observed at the 9 and 17 September assessments, with higher levels of
Botrytis and Sclerotinia as well as low levels of powdery mildew identified from 24
September with this continuing at the harvest assessment on 8 October. No phytotoxicity
was observed. The presence of powdery mildew is indicative of it being quite a dry year;
hence the absence of downy mildew ion the trial.
Table 16. Timing of sprays and assessments on outdoor lettuce trial, autumn 2015, Lincolnshire.
DateSpray timing
sAssessment carried out
22/07/2015 T1 Disease30/07/2015 Disease and Phytotoxicity06/08/2015 T2 Disease and Phytotoxicity13/08/2015 T3 Disease and Phytotoxicity20/08/2015 T4 Disease and Phytotoxicity27/08/2015 - Disease and Phytotoxicity09/09/2015 T5 Disease and Phytotoxicity17/09/2015 - Disease and Phytotoxicity24/09/2015 - Disease and Phytotoxicity30/09/2015 - Disease and Phytotoxicity08/10/2015 - Disease, Marketability and Yield
At the 30 September assessment, 3 weeks after the T5 application Botrytis was the main
pathogen present, with incidence ranging from 3.8% to 11.3%, and disease severity (0-100
index) ranging from 1.9 to 6.9. Significant but small treatment effects were observed in
Botrytis incidence (Fpr 0.028). None of the products applied in this trial have known activity
against Botrytis so these differences are unexpected but provide useful information on
product activity. Sclerotinia was present at low levels (0.0 – 2.5% incidence) (Table 17).
The destructive harvest disease assessment was completed on 8 October 2015 (Table 18).
Botrytis was still the main disease at this stage with disease incidence ranging from 73.8%
to 91.5%, and disease severity index (0-100) ranging from 47.5 – 66.1. No significant
treatment effects were observed, with a number of plots having category 3 symptoms with
lesions identified on the heads. Sclerotinia symptoms at this stage remained at relatively
low levels compared with Botrytis, and incidence ranged from 0 – 20%, with disease
Agriculture and Horticulture Development Board 2023. All rights reserved 42
severity index ranging from 0.0-4.4 with no significant treatment effects observed. At this
stage powdery mildew was also present at low levels within the trial, with powdery mildew
incidence ranging from 24-32% in the untreated control and least effective treatments to 0%
in the most effective treatment. Six treatments were found to be consistently and
significantly more effective than the untreated control; T13 & T14 (Amistar 1N & 0.5N rate
respectively), T15 & T16 (Fenomenal 1N & 0.5N rate respectively), T17 (F145) and T18
(F145 + Revus), with these treatments having a disease incidence of 5% or less and a
disease severity lower than 0.3%.
Yield and marketability was also assessed on 8 October, and included marketable weight
per 20 heads, average weight per marketable head and the percentage of heads which
were marketable per treatment (Table 19). Due to the number of Botrytis symptoms
present on the lettuce heads, marketability of the lettuce heads was low, with levels ranging
from 39% to 76% with no significant treatment trends observed. Yield per 20 heads ranged
from 6.5 – 12.3 kg, and the average weight per marketable head ranged from 0.58 – 0.79
kg/head. No significant yield effects were observed.
Agriculture and Horticulture Development Board 2023. All rights reserved 43
Table 17. Non-destructive Botrytis assessment, 30 September 2015.
Treatment no. Treatment Kg or
L/Ha
Sclerotinia BotrytisIncidence
(% of plants
affected)
Severity (Index 0-
100)
Incidence (% of plants
affected)
Severity (Index 0-
100)1 Untreated - 1.3 1.3 10.0 6.92 Untreated - 0.0 0.0 8.8 3.13 Fubol Gold 1.9 0.0 0.0 11.3 6.34 Fubol Gold 0.95 2.5 2.5 10.0 5.05 Invader 2 1.3 0.6 11.3 4.16 Invader 1 0.0 0.0 3.8 2.27 Revus 0.6 0.0 0.0 7.5 1.98 Revus 0.3 1.3 1.3 11.3 2.89 Infinito 1.6 0.0 0.0 6.3 2.2
10 Infinito 0.8 0.0 0.0 6.3 2.5
11 Previcur Energy 2.5 0.0 0.0 7.5 3.4
12 Previcur Energy 1.25 1.3 1.3 5.0 2.2
13 Amistar 1 0.0 0.0 7.5 3.414 Amistar 0.5 0.0 0.0 6.3 2.215 Fenomenal 2.5 2.5 2.5 10.0 4.116 Fenomenal 1.25 0.0 0.0 6.3 3.117 F145 2.5 0.0 0.0 5.0 2.5
18 F145 + Revus
2.5 + 0.3 1.3 1.3 7.5 4.4
Fpr 0.643 (ns) 0.605 (ns) 0.028 0.203 (ns)SED 1.37 1.32 2.33 1.75LSD 2.74 2.64 4.68 3.50
Agriculture and Horticulture Development Board 2023. All rights reserved 44
Table 18. Destructive disease assessment at harvest in 8 October 2015.
Treatment no. Treatment Kg or
L/Ha
Powdery mildew Sclerotinia BotrytisIncidence (% of plants
affected)
Severity (% leaf
area affected)
Incidence (% of plants
affected)
Severity (0-100 index)
Incidence (% of plants
affected)
Severity (0-100 index)
1 Untreated - 24 1.8 5 0.3 82.5 57.52 Untreated - 24 1.9 10 0.9 88.8 59.43 Fubol Gold 1.9 18 0.6 10 2.2 92.5 64.74 Fubol Gold 0.95 12 0.9 5 1.3 73.8 47.55 Invader 2 19 0.8 0 0.0 85.0 60.36 Invader 1 4 0.1 5 0.3 61.3 38.87 Revus 0.6 24 1.8 0 0.0 87.5 60.08 Revus 0.3 22 0.9 0 0.0 87.5 60.99 Infinito 1.6 32 2.2 5 0.9 77.5 54.4
10 Infinito 0.8 22 1.1 5 0.9 86.2 63.1
11 Previcur Energy 2.5 21 0.9 0 0.0 86.2 55.3
12 Previcur Energy 1.25 15 0.7 10 1.9 85.0 56.9
13 Amistar 1 0 0.0 0 0.0 90.0 63.414 Amistar 0.5 2 0.1 0 0.0 80.0 55.015 Fenomenal 2.5 4 0.1 5 0.3 90.0 62.516 Fenomenal 1.25 3 0.2 5 0.3 91.5 66.117 F145 2.5 2 0.1 20 4.4 83.8 62.8
18 F145 + Revus
2.5 + 0.3 5 0.1 0 0.0 90.0 61.9
Fpr 0.005 0.039 0.663 (ns) 0.331 (ns) 0.167 (ns) 0.674 (ns)SED 8.9 0.74 2.1 1.48 8.99 10.46LSD 18.0 1.48 4.1 2.97 18.06 21.01
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Table 19. Results of the yield assessment, 8 October 2015, Lincolnshire.
Treatment no. Treatment Kg or
L/HaYield Marketability
Marketable yield per plot (kg)
Mean marketable head weight (g)
% of heads marketable
1 Untreated - 9.3 700 532 Untreated - 10.6 680 623 Fubol Gold 1.9 8.9 640 564 Fubol Gold 0.95 11.1 770 575 Invader 2 8.8 760 486 Invader 1 10.7 630 727 Revus 0.6 12.2 690 718 Revus 0.3 9.5 750 509 Infinito 1.6 9.7 720 54
10 Infinito 0.8 9.9 690 58
11 Previcur Energy 2.5 8.9 710 50
12 Previcur Energy 1.25 10.3 680 60
13 Amistar 1 6.5 680 3914 Amistar 0.5 12.3 790 6215 Fenomenal 2.5 9.6 640 6016 Fenomenal 1.25 11.4 610 7617 F145 2.5 9.5 580 67
18 F145 + Revus
2.5 + 0.3 6.5 660 42
Fpr 0.335 (ns) 0.194 (ns) 0.302 (ns)SED 2.10 69 12.9LSD 4.21 139 25.9
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In the third year of this project information was produced on both fungicide programme
formation and product efficacy for the control of downy mildew in a low disease situation.
This provided a contrast to the outdoor lettuce experiment in Year 2 where products were
tested under severe disease pressure. September 2014 had above average temperatures
and below average rainfall. The crop was also small and low in density which would aid air
movement which combined with the weather was not ideal for downy mildew to readily
infect and reproduce. Products were being tested in a protectant situation, so no downy
mildew was present at the first spray timing and only trace levels at T2, T3 and T4. It was
shown that preventative control of downy mildew early on in an epidemic can result in
prolonged disease control, of up to four weeks, after the final spray. This is obviously
beneficial with regards to minimising residue levels.
The standard programme based on the most effective programme against downy mildew
from the 2013 trials was again one of the most effective either as four (Treatment 2) or five
(Treatment 3) sprays, containing the product combinations of Amistar, Karamate, Signum,
Invader, Infinito, Fubol Gold and Revus. All nine programmes with Invader (dimethomorph +
mancozeb) as a tank mix at Timing 2 had significantly fewer plants with downy mildew at
harvest. The other programme with a significantly lower incidence of downy mildew used a
tank mix of the experimental product F147 in place of Invader at Timing 2 (plus two further
successive applications) and this gave the overall best control with just 0.15% leaf area
affected and only 19% of heads with any disease when compared with the standard.
Experimental product F189 included in a programme and applied at the 1st and 3rd timing,
allowed the number of conventional fungicides to be reduced and gave similar efficacy with
regards to % leaf area affected. This was not significantly different from the conventional
fungicide programmes. Additionally, 45% of heads were affected and this was higher
(although not significantly so) than in the standard programmes.
Previous trials in this project have consistently demonstrated that Fubol Gold and Revus at
the last two treatment application timings (Timings 3 and 4), provide the strongest and most
effective treatment programme components. This combination of chemicals was utilised
again in the autumn 2014 trial and again maintained good control of downy mildew severity.
Reducing broad spectrum actives at the start of the programmes to half rates did not
significantly lessen the control against downy mildew in this low disease situation. It is
important to note that all the fungicides targeting downy mildew applied from the third timing
onwards were at full rates, and disease was not observed at more than trace levels until the
fifth application timing.
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Paraat does have label use in lettuce for the control of downy mildew and has good activity
against Oomycetes but, surprisingly, in this experiment the application of Paraat at Timing 4
did not result in significant disease control and this may mean that earlier application
timings need to be considered.
Residues were found two weeks after the last treatment timing for certain actives, with the
majority of residues being found from the application of dithiocarbamate treatments. None
of the levels were near MRLs, however this result does highlight the importance of the
positioning of certain products.
Protected Trials
Autumn 2014
The lettuce crop established well and infection was not noted until three weeks after
planting following two foliar spray applications. Usually at this time of year downy mildew
would be the prevalent foliar disease, but in this trial, perhaps influenced by the high soil-
borne inoculum pressure, the main disease was bottom rot (Rhizoctonia solani) which was
severe and caused significant crop damage and plant death. Significant differences in
Rhizoctonia control between treatments were found (Table 20, Figure 6). Sclerotinia
infection was moderate-high but there were no significant differences between treatments.
Sclerotinia did not primarily infect the lower senescing leaves of the plants as mycelium, but
instead infected the upper canopy probably via ascospore infection utilising the necrotic leaf
tissue of those plants which had tipburn (Figure 7). Downy mildew incidence ranged from
10% to 50% plants infected depending on treatment, but the overall severity of infection was
low. Botrytis levels were very low, but may have been masked by the high levels of
Rhizoctonia and Sclerotinia. Phytotoxicity was seen in treatment 11, following application of
experimental product HDC F159 (Figure 7), but the treated plants soon recovered.
The first detailed disease assessment on 02/09/14 was made after two treatment
applications had been made (Table 20). There was high incidence of Rhizoctonia in the
untreated control. There were significant treatment effects, with best control of Rhizoctonia
being achieved with spray programmes that included Amistar or an SDHI fungicide. This
reflects the results seen in the spring 2013 protected lettuce trial where treatments
containing early applications of Amistar performed well at controlling Rhizoctonia. T3
(Contans/Amistar/Fubol Gold) performed best (disease incidence 23%) and had
significantly lower disease severity than the other treatments. Treatments 5
(Contans/Amistar/Paraat), 7 (half rate tank mixes of Amistar + Fubol Gold/Signum + Switch)
and 10 (HDC F187/half rate tank mixes of Amistar + Fubol Gold) also controlled Rhizoctonia
Agriculture and Horticulture Development Board 2023. All rights reserved 48
well (disease incidences 41%, 33% and 35% respectively). By this stage in the trial downy
mildew had appeared but at relatively low levels too (Figure 8).
Agriculture and Horticulture Development Board 2023. All rights reserved 49
Table 20. Disease severities (0-3 scale) and percentage of dead plants at the first assessment (02/09/14) following a pre-planting application and two treatment applications.
Treatment Pre-planting
2-3 days post-planting
10-14 DAT Disease Severity 02/09/14* % dead
No. Programme 7/8/14 12/8/14 22/8/14 Bremia Botrytis Rhizoctonia Sclerotinia plants1 Control Untreated
(water)Untreated
(water)0.01a 0.01a 0.95a 0a 0a
2 Standard 1N Amistar 1N Fubol Gold 0.05a 0a 0.36bcd 0.03a 0a3 Commercial Contans 1N Amistar 1N Fubol Gold 0.02a 0.02a 0.10e 0a 0a4 Commercial Contans 1N Paraat 1N Amistar 0a 0.01a 0.45bc 0.01a 1.25a5 Commercial Contans 1N Amistar 1N Paraat 0.02a 0.01a 0.20cde 0a 0a6 Commercial 1N Fubol Gold 1N Switch 0.01a 0.01a 0.47b 0a 2.50a7 Experimental
Commercial0.5N Amistar +
0.5N Fubol Gold0.5N Signum +
0.5N Switch0a 0.01a 0.20de 0.01a 0a
8 Experimental Commercial
0.5N Signum +0.5N Fubol Gold
0.5N Paraat +0.5N Octave
0a 0a 0.36bcd 0a 0a
9 Experimental Commercial
0.5N Signum +0.5N Fubol Gold
- 0.01a 0.01a 0.41bcd 0a 0a
10 Experimental 1N HDC F187 0.5N Amistar + 0.5N Fubol Gold
0.03a 0a 0.20de 0.01a 1.25a
11 Experimental 0.5N HDC F153 + 0.5N Signum
1N HDC F159 0a 0a 0.34bcd 0a 0a
12 Experimental 1N HDC F151 0.5N Infinito +0.5N HDC F150
0a 0a 0.31b-e 0a 1.25a
*values followed by the same letter are not significantly different
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1 2 3 4 5 6 7 8 9 10 11 120
10
20
30
40
50
60
70
80
90
100
Disease Incidence
02/09/2014 12/09/2014 22/09/2014
dise
ase
incid
ence
(%)
1 2 3 4 5 6 7 8 9 10 11 120
0.25
0.5
0.75
1
1.25
1.5
1.75
2
2.25
2.5
Disease severity
02/09/2014 12/09/2014 22/09/2014di
seas
e se
verit
y (0
-3 sc
ale)
Figure 6. Rhizoctonia incidence (%) and severity (disease Index 0-3) recorded in the autumn 2014 protected trial.
Agriculture and Horticulture Development Board 2023. All rights reserved 51
Figure 7. Phytotoxicity symptoms, marginal leaf necrosis and examples of the untreated plots and plots treated with an effective fungicide programme.
Agriculture and Horticulture Development Board 2023. All rights reserved 52
1 2 3 4 5 6 7 8 9 10 11 120
10
20
30
40
50
60
70
80
90
100
Disease incidence
02/09/2014 12/09/2014 22/09/2014
dise
ase
incid
ence
(%)
1 2 3 4 5 6 7 8 9 10 11 120
0.25
0.5
0.75
1
1.25
1.5
1.75
2
2.25
2.5
Disease Severity
02/09/2014 12/09/2014 22/09/2014di
seas
e se
verit
y (0
-3 sc
ale)
Figure 8. Downy mildew incidence (%) and severity (disease Index 0-3) recorded in the autumn 2014 protected trial.
Agriculture and Horticulture Development Board 2023. All rights reserved 53
Table 21. Disease severities (0-3 scale) and percentage of dead plants at the second assessment (12/09/14) following a pre-planting application and three treatment applications (values followed by the same letter are not significantly different).
Treatment Pre-planting
2-3 days post-planting 10-14 DAT 10-14 DAT Disease Severity 12/09/14* % dead
No. Programme 7/8/14 12/8/14 22/8/14 1/9/14 Bremia Botrytis Rhizoctonia Sclerotinia plants
1 Control Untreated (water) Untreated (water) Untreated (water) 0.21ab 0a 1.76a 0.82a 27.32a
2 Standard 1N Amistar 1N Fubol Gold 1N Switch 0.10a-d 0a 1.21bcd 1.01a 9.25bc
3 Commercial Contans 1N Amistar 1N Fubol Gold 1N Paraat 0.01d 0a 0.86d 0.73a 2.41bcd
4 Commercial Contans 1N Paraat 1N Amistar 1N Switch 0.23ab 0a 1.24bc 1.12a 13.32ab
5 Commercial Contans 1N Amistar 1N Paraat 1N HDC F145 0.29a 0a 1.16bcd 0.64a 0.32d
6 Commercial 1N Fubol Gold 1N Switch 1N Signum 0.08bcd 0a 0.99bcd 0.71a 2.41bcd
7 Experimental Commercial
0.5N Amistar +0.5N Fubol Gold
0.5N Signum +0.5N Switch
0.5N Paraat +0.5N Octave 0.13abc 0a 1.02bcd 0.93a 6.49bcd
8 Experimental Commercial
0.5N Signum +0.5N Fubol Gold
0.5N Paraat +0.5N Octave
0.5N Amistar + 0.5N Revus 0.08a-d 0a 1.33b 0.66a 5.48bcd
9 Experimental Commercial
0.5N Signum +0.5N Fubol Gold - 0.5N Switch +
0.5N Revus 0.22ab 0a 1.33b 0.92a 7.47bcd
10 Experimental 1N HDC F187 0.5N Amistar +0.5N Fubol Gold
0.5N HDC F152 + 0.5N Revus 0.03cd 0a 0.87cd 0.88a 0.65cd
11 Experimental 0.5N HDC F153 + 0.5N Signum 1N HDC F159 0.5N HDC F153
+ 0.5N Signum 0.05bcd 0a 1.32b 0.61a 4.00bcd
12 Experimental 1N HDC F151 0.5N Infinito +0.5N HDC F150
0.5N HDC F151 + 0.5N HDC
F1500.04cd 0a 1.05bcd 0.55a 2.94bcd
*values followed by the same letter are not significantly different
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There were no significant differences between treatments. There were very low levels of
Botrytis and Sclerotinia recorded at the first assessment (<4% incidence).
The second disease assessment was made on 12/09/14 following the third treatment
application (Table 21). By this stage the incidence of Rhizoctonia had risen to 100% in the
untreated control. Control of the disease correlated well with the previous assessment:
treatments 3, 7 and 10 having the lowest disease severities (0.86, 1.02 and 0.87
respectively). Treatment 6 (Fubol Gold/Switch/Signum), following the application of
Signum, improved control of Rhizoctonia in relation to the other treatments. There were
significant treatment effects for downy mildew (disease incidence ranged from 12% to 60%)
and good control of this disease was also achieved by some of the same treatment
programmes that provided good control of Rhizoctonia: notably treatments 3 and 10 having
disease incidences of 12.5% and 20% respectively. The exception was treatment 5 which
had the highest incidence of downy mildew (60%) following the application of an
experimental biological product, HDC F145. No Botrytis was recorded and Sclerotinia
levels were medium (40%-70% incidence) but not significantly different between treatments.
Rhizoctonia was responsible for most of the plant deaths, but generally there were fewer
plant deaths in treatments where the third application had been an SDHI at either half or full
rate. Significantly fewer plants had died in treatments 5 and 10 (0.32% and 0.65%
respectively) than in many of the other treatments (percentage of dead plants ranged from
2% to 13%). A significantly higher number of plants died in the untreated (27%).
Control of both Rhizoctonia and downy mildew was good in the first two assessments with
programmes containing a combination of Contans, Amistar, Fubol Gold, Paraat and an
SDHI active ingredient e.g. boscalid (in Signum). This was also noted in the previous
glasshouse trial in Spring 2013.
By the third assessment on 22/09/14 levels of Rhizoctonia and Sclerotinia were high in all
plots (93%-100% and 55%-85% incidences respectively) and many of the remaining plants
died from Sclerotinia infection. Sclerotinia infected marginal necrosis of leaves via
ascospores. There were no significant differences between treatments for any of the
diseases assessed.
At harvest there were no significant differences between treatments for disease control or
head weight, but sample sizes were low due to the number of plants that had died.
Autumn 2015
The Autumn 2015 protected trial focused on control of downy mildew using a split plot
arrangement of two cultivars to increase the risk of downy mildew. However, occurrence of
this usually common disease was sporadic due to unfavourable environmental conditions.
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It wasn’t until four weeks after the third post-planting treatment application that downy
mildew was observed in the untreated plots. By this time the crop would normally have
been harvested but in order to collect data on the longevity of the treatments the trial was
extended by a further two weeks.
No downy mildew was recorded on the commercial variety, Brian, demonstrating the
importance of resistance genes incorporated into modern varieties. There was low to
medium incidence of downy mildew on Cobham Green (an older cultivar with fewer downy
mildew resistance genes) in the untreated plots and very low incidence of downy mildew on
this variety in some of the treatments, including those where half rates had been applied
and in some treatments these differences were significant (Table 22). All treatments had a
significantly lower incidence of downy mildew than the untreated. No downy mildew was
recorded in treatments 7 & 8 (Paraat/ Revus at 1N & 0.5N rates respectively). No downy
mildew was recorded in treatment 2 (1N rates of Amistar/ Fubol Gold/ Paraat/ Serenade);
very low, but not significant, incidence (0.82%) was recorded in treatment 3 (0.5N rates of
Amistar/ Fubol Gold/ Paraat/ Serenade) at all three assessments. In treatments 5 & 6
(Amistar + Fubol Gold/ Paraat/ Revus at 1N & 0.5N rates respectively) downy mildew was
only recorded (incidence 0.82%) in the final assessment of the 1N rate although this was
not significant. In treatment 7 (Amistar + Fubol Gold/ Paraat + Revus at 0.5N rates) no
downy mildew was recorded in the first two assessments but significantly higher incidence
of downy mildew (5.04%) was recorded at the final assessment. In treatments 9 & 10
(F150/ Previcur Energy/ Infinito/ Serenade at 1N & 0.5N rates respectively) downy mildew
was only recorded in the final assessment of the 0.5N rate (incidence 0.82%) although this
was not significant. Downy mildew was recorded in treatments 11 & 12 (F146/ Invader/
F150/ Serenade at 1N & 0.5N rates respectively) and this was significant at the 1N rate at
the first assessment (incidence 2.32%).
Although there were no significant differences in disease incidence or severity between
treatments for the lettuce variety Brian, there were significant differences in mean head
weights at harvest (Table 23). The highest head weights were recorded in treatments 2 & 3
(Amistar/ Fubol Gold/ Paraat/ Serenade at 1N & 0.5N rates respectively) (0.163 kg & 0.159
kg marketable weights respectively) and these were significantly heavier than those
recorded in 7 & 8 (Paraat/ Revus at 1N & 0.5N rates respectively) (0.121 kg & 0.116 kg
marketable weights respectively) which were not significantly different from the untreated
control (0.110 kg marketable weight). Some fungicide products also have additional
benefits e.g. turning on of host defences, leaf greening and strengthening of plant cell walls
which could result in increased head weight at harvest (in the absence of disease) and it
may be that these were playing a part here.
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Table 22. Incidence of downy mildew in variety Cobham Green at three assessments in autumn 2015 protected trial.
Application timings Downy Mildew Incidence (%)
Trt. 6 days after planting 7 days after T1 13 days after
T228 days after
T327 days after T3
7 days after T4
13 days after T4
1 Untreated Untreated Untreated Untreated 25.7a 15.61a 51.1a2 Amistar 1N Fubol Gold 1N Paraat 1N Serenade 1N 0c 0b 0c
3 Amistar 0.5N Fubol Gold 0.5N Paraat 0.5N Serenade 1N 0.82bc 0.82b 0.82c
4 Amistar 0.5N + Fubol Gold 0.5N Paraat 1N Revus 1N - 0c 0b 0.82c
5 Amistar 0.5N + Fubol Gold 0.5N Paraat 0.5N Revus 0.5N - 0c 0b 0c
6 Amistar 0.5N + Fubol Gold 0.5N - Paraat 0.5N +
Revus 0.5N - 0c 0b 5.04b
7 Paraat 1N - Revus 1N - 0c 0b 0c8 Paraat 0.5N - Revus 0.5N - 0c 0b 0c
9 F150 1N Previcur Energy 1N Infinito 1N Serenade 1N 0c 0b 0c
10 F150 0.5N Previcur Energy 0.5N Infinito 0.5N Serenade 1N 0c 0b 0.82c
11 F146 1N Invader 1N F153 1N Serenade 1N 2.32b 1.14b 0.82c12 F146 0.5N Invader 0.5N F153 0.5N Serenade 1N 0.82bc 0.82b 0c
LSD (P=.05) 0.422t 0.537t 0.500tSt. Dev. 0.292t 0.372t 0.346t
Grand Mean 0.21t 0.17t 0.29tProb(F) 0.0001 0.002 0.0001
Numbers followed by the same letter are not significantly different.
Table 23. Mean head weights of lettuce variety Brian at harvest.Application timings Mean head weight (g)
Trt. 6 days after planting 7 days after T1 13 days after
T228 days after
T3 Untrimmed Trimmed
1 Untreated Untreated Untreated Untreated 194d 110d2 Amistar 1N Fubol Gold 1N Paraat 1N Serenade 1N 238a 163a3 Amistar 0.5N Fubol Gold 0.5N Paraat 0.5N Serenade 1N 227ab 159ab
4 Amistar 0.5N + Fubol Gold 0.5N Paraat 1N Revus 1N - 215a-d 139a-d
5 Amistar 0.5N + Fubol Gold 0.5N Paraat 0.5N Revus 0.5N - 208bcd 131a-d
6 Amistar 0.5N + Fubol Gold 0.5N - Paraat 0.5N +
Revus 0.5N - 214bcd 134a-d
7 Paraat 1N - Revus 1N - 203cd 121cd8 Paraat 0.5N - Revus 0.5N - 196d 116d9 F150 1N Previcur Energy 1N Infinito 1N Serenade 1N 206bcd 134a-d
10 F150 0.5N Previcur Energy 0.5N Infinito 0.5N Serenade 1N 204bcd 130bcd11 F146 1N Invader 1N F153 1N Serenade 1N 220abc 153abc12 F146 0.5N Invader 0.5N F153 0.5N Serenade 1N 204bcd 127bcd
LSD (P=.05) 23.6 32.3St. Dev. 16.3 22.4
Grand Mean 210 130Prob(F) 0.0217 0.0415
Numbers followed by the same letter are not significantly different.
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Although Paraat and Revus appear to be the most effective products at controlling downy
mildew from the results in the Cobham Green plants, the lowest head weights, not
significantly different from the untreated, were recorded in the lettuce cultivar Brian in these
treatments at harvest.
Incidence of Botrytis in the variety Cobham Green was medium to high, affecting both lower
leaves and outer leaves, but there were no significant differences between treatments.
Incidence of Botrytis in the variety Brian was low to medium, only affecting lower leaves of
the crop, but there were no significant differences between treatments. Rhizoctonia and
Sclerotinia also occurred in both varieties, but at low, insignificant levels.
Conclusions
Outdoor Lettuce
No new integrated spray programmes were significantly more effective than the
commercial standard programmes
Sequential experimental product F147 used instead of mancozeb (in Invader and Fubol
Gold) in tank mixes within a programme gave good downy mildew control
Fubol Gold and Revus were consistently strong against downy mildew at the end of
programmes
The benefit of certain biological fungicide products were shown as alternative to
conventional fungicides at certain timings in the programme
Reducing broad spectrum actives at the start of the programmes to half rates did not
significantly impact on the control of downy mildew in this low disease situation.
Residues were not found to exceed any of the MRLs, although the results did highlight
the importance of the positioning of certain products in spray programmes.
Protected Lettuce
A number of programmes utilising approved products controlled Rhizoctonia and downy
mildew reasonably well under low to medium disease pressure. These could make an
effective replacement for the organophosphate Basilex.
Programmes containing a combination of Contans, Amistar, Fubol Gold, Paraat and
Signum were effective at controlling downy mildew, Rhizoctonia and Sclerotinia.
Programmes containing Paraat and/or Revus as alternatives to Fubol Gold can provide
a good downy mildew control enabling shorter harvest intervals and reduce the risk of
resistance to metalaxyl developing in Bremia lactucae populations.
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There is some evidence to suggest that reduced (0.5N) rates of active ingredients
(applied as various tank mixes) remained largely effective thus potentially providing an
opportunity for broader disease control with a reduced risk of resistance development
and/or pesticide residues at harvest, though some caution will be required under high
disease pressure situations.
Data on Botrytis in these trials were limited, but by controlling other diseases, principally
downy mildew, Botrytis problems should be reduced as the opportunistic nature of this
fungus means it will have more limited opportunity to infect damaged tissues caused by
other disease pathogens.
Knowledge and Technology Transfer
February 2015 project review meeting
Two articles for AHDB Grower magazine:
‘Cut fungicides and keep control’ (protected lettuce) written by James Townsend published
in July/August 2015
‘Programmes for the autumn schedule’ (outdoor lettuce) written by Angela Huckle published
in September 2015.
References
Gladders, P., Green, K., Huckle, A. and Kirkpatrick, L. (2010). Outdoor lettuce: evaluation
of novel fungicides for downy mildew control. Horticultural Development Company Final
report for project FV 357.
Horticultural Statistics (2014). Published by the Department for Environment, Food and
Rural Affairs.
Agriculture and Horticulture Development Board 2023. All rights reserved 59