Project title:€¦ · Web viewProject title: Lettuce: Further development of ‘Best Practice’ for disease control in protected and outdoor crops Project number: FV/PE 410 Project

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

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Development Board accepts no liability for loss, damage or injury howsoever caused

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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 ............................................


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.


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.

Agriculture and Horticulture Development Board 2023. All rights reserved 5

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


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


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.


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).


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.


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.


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.


http://www.frac.info/docs/default-source/publications/frac-code-list/frac-code-list-2016.pdf?sfvrsn=2

http://www.frac.info/docs/default-source/publications/frac-code-list/frac-code-list-2016.pdf?sfvrsn=2

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.


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.


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.


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


(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 F188 (experimental biological product) - -

HDC F189 (experimental product) - -


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 -


Signum +Invader Infinito Fubol Gold Revus


Signum +Invader Infinito Revus HDC F145


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


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.


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


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.


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,


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


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.


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.


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.


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.


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


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).


Sclerotinia spp.


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,


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


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.


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.


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.




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).


The data for the indoor trials were analysed by Analysis of Variance (ANOVA) using ARM 9

statistical software package (Gylling Data Management Inc.).


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 -


0.5N Paraat 0.5N Revus -

Experimental commercial 2 spray programmes


- 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


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.



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


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.


The data for the indoor trials were analysed by Analysis of Variance (ANOVA) using ARM 9

statistical software package (Gylling Data Management Inc.).


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




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


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


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.


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


0.5N HDC F151 + Invader PrevicurEnergy Infinito Revus 38.8 0.4


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


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


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 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).


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.


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



7 HDC F150 Previcur Energy +HDC F151



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


0.5N HDC F151 + Invader Previcur Energy Infinito Revus 60.0 18.8


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


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)


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






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


0.5N HDC F151 +Invader

Previcur Energy Infinito Revus 21.2 8.1


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


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


Infinito Revus 12.83 97.5 660


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



Previcur Energy Infinito Revus 12.88 97.5 660


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


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.


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


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.


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)


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


Table 18. Destructive disease assessment at harvest in 8 October 2015.


L/Ha

Powdery mildew Sclerotinia BotrytisIncidence (% of plants

affected)

Severity (% leaf

area affected)


affected)



affected)


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


Table 19. Results of the yield assessment, 8 October 2015, Lincolnshire.


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


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.


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


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).


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



- 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


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.


Figure 7. Phytotoxicity symptoms, marginal leaf necrosis and examples of the untreated plots and plots treated with an effective fungicide programme.


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.


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


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



0.5N Paraat +0.5N Octave

0.5N Amistar + 0.5N Revus 0.08a-d 0a 1.33b 0.66a 5.48bcd


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


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.


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.


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.


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.


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.


Documents

Project title:€¦ · Web viewProject title: Lettuce: Further development of ‘Best Practice’ for disease control in protected and outdoor crops Project number: FV/PE 410 Project