Blackleg and light leaf spot research and management update from the UK

Dr Faye Ritchie, ADAS Boxworth, Cambridgeshire, UK

ADAS: an independent crop research and consultancy business and part of RSK group plc

faye.ritchie@adas.co.uk

Outline

• Overview of vegetable (focus on cruciferous crops) production in the UK

• Phoma and light leaf spot epidemics

• Risk factors (area wide and residue management, rotation, burial, seed infection)

• Fungicide efficacy (FP and product list) and resistance.

Brassica production in Europe and the UK

• Europe – 15 million acres canola

• 1.1 million acres brassica vegetables

• UK Horticultural industry worth $3.8 billion (ornamentals, fruit and vegetables)

• Home production of vegetables = 57% UK supply (Import from Spain and Netherlands)

• Brassica vegetables = 440,000 tonnes produced ($215 million)

Horticultural statistics, 2015

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Brassica vegetable area in the UK

Brassica vegetable area (acres) in 2015 in the UK – by crop

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Cauliflower Broccoli Cabbage, Winter Brussels Sprouts Rutabaga and

turnips

Cabbage, Spring Cabbage, Summer

and Autumn

Horticultural statistics, 2015

Brassica cropping area (acres) in the UK including canola in 2015

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Oilseed rape Cauliflower Broccoli Cabbage,

Winter

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Cabbage,

Summer and

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Horticultural statistics, 2015

Area wide management - increasing canola area

https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/183108/defra-

stats-foodfarm-landuselivestock-june-detailedresults-cropmaps111125.pdf

Main areas of brassica

vegetable production

Other diseases affecting brassica vegetables in the UK

Targeting a range of diseases with fungicides on vegetable brassicas in the UK in 2015

63%10%

10%

4%

4%4% 2% 2% 1%

General disease control Alternaria/ringspot Alternaria/light leaf spot

Light leaf spot Botrytis White blister

Ringspot Leaf spot/phoma Downy mildew

Pesticide usage survey, 2015

97% crops receive chemical seed treatment

97% crops receive at least 3 fungicide

applications

Blackleg and light leaf spot management in the UK on brassica vegetables

• Occurs along with controlling other diseases: products can be selected to control a range of diseases

• Local knowledge and crop monitoring key to guiding decisions

• Risk periods differ for phoma and light leaf spot – different requirements for spore release, infection and spread

Phoma leaf spot and stem canker (blackleg)

Phoma A = Leptosphaeria maculans Phoma B = Leptosphaeria biglobosa Stem canker

(blackleg)

Phoma leaf spot epidemics on canola (England and Wales since 2008) – fungicide treated crops

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60

November March

Pe

rce

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ge o

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ts a

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cte

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ati

on

ally

2008 2009 2010 2011 2012 2013 2014 2015

Source: DEFRA canola disease survey

Phoma leaf spot and stem canker (blackleg) on vegetable brassicas

• Two species – Leptosphaeria maculans and L. biglobosa

• Severe losses in cauliflower (rare) and rutabaga – leaf blemish in other crops

• Leaf symptoms from cotyledon stage onwards – can require early management

Phoma leaf spot produces air-borne spores under UK conditions

Sep

Jan

Mar

Nov

May

Jul

Phoma leaf spot

Air-borne spores only

Determining risk - Phoma forecast in the UK (canola but not vegetable brassicas)

• Time to 10% leaf spotting in canola (October onwards)

• Provides date to determine risk and map turns green, amber then red once date is reached/has passed

• Potential to develop risk assessment for vegetable brassicas

http://www.rothamsted.ac.uk/phoma-leaf-spot-forecast/phoma-forecast

[1] Time of 10 %

leaf spotting

[3] Increase in

canker severity

[4] Yield loss vs

canker severity

[2] Time between leaf

spotting and canker

Air-borne

spores

produced

(faster with

continuous

wetness of

debris)

No spore

release at sub

zero

temperatures

130 to 160 degree C

days (e.g. 15 days at

50˚F or 10 days at

59˚F)

e.g. 100 days at 54˚F

20 days with

rain from 1

August

The earlier canker is first seen, longer it

has to develop until harvest

Earlier epidemics have potential

to cause largest yield losses

Production and release of ascospores (airborne spores) on crop debris

• Sources of phoma include infected seed, infected seed crop and canola stems (winter and spring)

• Ascospores (air-borne spores) produced where canker has formed (blackleg) – some crops only affected by leaf spots e.g. harvested prior to canker development.

Rotation and crop residue management – phoma (blackleg)

• Longer burial decreases spore production on crop debris

Data from Huang et al 2003 Annals of Applied Biology 143: 359-369

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2 months 12 months

Duration of burial

Percentage of debris with pseudothecia

Number of pseudothecia per m2

Rotation and crop residue management (phoma)

• Proximity to crop debris increases risk of phoma leaf spot and blackleg

Data from Gladders and Musa, 1980 Plant Pathology 29:28 - 37

>1500m

400 to 800m

<40m

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UnploughedPloughed Site 1

Ploughed site 2Ploughed site 3

Ploughed site 4

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(m)

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of

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ea

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ot

Site ploughed or unploughed

Proximity to crop debris and development of leaf spot in canola (mid-November)

Seed health important to prevent spread of pathogen and races

• Variety resistance breakdown observed

• Control of seed borne phoma – seed treatment

• Seed borne light leaf spot – not as well understood as phoma and no control measures at present

• Future – develop molecular seed tests for a range of plant pathogens (e.g. light leaf spot, verticillium stem stripe)

Understanding development of phoma dry rot in rutabaga – AHDB Horticulture Project FV 431 (2014/2015)

• Dry rot caused by same pathogen causing stem canker in canola (Leptosphaeria maculans) –pathogenicity of L. biglobosaunknown

• Root infection in the absence of leaf infection reported

• Disease cycle not fully understood on rutabaga

Understanding development of phoma dry rot in rutabaga - key findings

• L. maculans and L. biglobosa cause dry rot on rutabaga

• Leaf symptoms occur in crops earlier than in canola – first root symptoms after 6 months (January).

• Root wounding increased the proportion of crop affected and the severity of internal symptoms

• Ascospores initiate epidemics but pynidiospores also infective and are produced on infected roots – role in infection?

•White spore droplets: acervuli

• Yellowing; bleached and

brittle lesions

• Leaf distortion & stunting

• Stem, petiole and pod

infections

• Dark pigmentation

(vegetable brassicas)

On canola (stunting) On Brussels sprouts

On cabbage

Light leaf spot on vegetable brassicas

Courtesy of Coretta Kloppel, University of Hertfordshire

Light leaf spot – canola leaves and stems

Light leaf spot is capable of continued cycling under UK conditions

Sep

Jan

Mar

Nov

May

Jul

Cycles in the crop – switches spore typeAir-borne spores

Light leaf spot

Phoma leaf spot

Air-borne spores only

Light leaf spot epidemics on canola (levels in the spring in England and Wales since 2008)

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% crops % plants

2006 2007 2008 2009 2010 2011 2012 2013 2014 2015

Source: DEFRA canola disease survey

Light leaf spot on Brussels sprouts 1983-1985 – more disease in Brussels sprouts grown adjacent to canola fields

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1983 1984 1985

% p

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s a

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cte

d

Leaves adjacent Buttons adjacent Leaves distant Buttons distant

Air-borne spore development and release – key criteria

• Air-borne spores produced on petioles, pods and stems

• Temperature and moisture affect apothecia maturation

• 6 to 7 weeks to form on canola petioles

• Dry conditions delay spore maturation and release but don’t prevent it From: Gilies, 2000 PhD Thesis, Waginengen

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43 49 55 63 65 72

Temperature (˚F)

Maximum no. apothecia per petiole length

Peak production of ascospores (days after inoculation)

Duration of ascospore production (total days)

In-crop spore development – key criteria

• Switches to different spore type: allows further spread via rainsplashwithin the crop and disease can appear patchy

• Optimum temperature for infection = 61˚F but active from 40˚F to 68˚F

(note: not tested but likely to be active <4˚F )

• High humidity = infection possible at lower temperatures

• Similar disease levels at 61˚F with 6h leaf wetness and 46˚F with 16h leaf wetness

• Disease severity declines above 68˚F, no disease at 75˚F

From: Gilies, 2000 PhD Thesis, Wageningen

Determining risk – weather based risk for assessing light leaf spot risk in the UK on canola

Percentage of canola crops with >25% affected plants at stem extension

http://www.rothamsted.ac.uk/light-leaf-spot-forecast/historical-trends-light-leaf-spot

Current research: Investigating components of the canola light leaf spot epidemic responsible for increased yield loss to the UK

• To develop novel decision support tool to predict

epidemic onset

• Verify model output through qPCR of spore samples

• Model disease cycling to improve understanding of

epidemic

• Update current light leaf spot forecast in canola

(potential for use on vegetable brassicas)

AHDB Project: RD-2012-3814

When are air-borne spores produced and released during the season? (spore trap data from 2015)

Massive dispersal of ascospores by

harvesting infected crops and

stubble cultivation

Crop emergence (canola)

Following initial infection by

ascospores, LLS cycles in the

crop by rain-splashed conidia

which will not be picked up by

spore trapping

Pb = Pyrenopeziza brassicae

AHDB project RD3814 – data from Rothamsted in 2015

Fungicide active ingredients used on vegetable brassicas in the UK in 2015

16.7

15.2

12.5

12.5

12.3

8.9

8.1

5.1

4.1

3.01.1 0.6 0.1 0.1

Horticultural statistics, 2015

16.7

15.2

12.5

12.5

12.3

8.9

8.1

5.1

4.1 3.0

1.10.60.10.1

Difenoconazole

Azoxystrobin/difenoconazole

Tebuconazole/trifloxystrobin

Prothioconazole

Boscalid/pyraclostrobin

Copper oxychloride

Azoxystrobin

Mancozeb/metalaxyl-M

Chlorothalonil/Metalaxyl-M

Metalaxyl-M

Fluopicolide/Propamocarb-hydrochloride

Tebuconazole

Dimethomorph/mancozeb

Others

Determining the effectiveness of fungicides against phoma leaf spot/stem canker and light leaf spot on canola (information also used by vegetable crop advisors)

Target Disease Site (Variety) Organisation

Phoma

(2-spray*)

Boxworth, Cambs (2015-16 cv. Catana) ADAS

Terrington, Norfolk (2015-16 cv. Catana) ADAS

Light Leaf Spot

(2-spray**)

Malton, North Yorks (2015-16 cv. PR46W21) ADAS

Dorset (2015-16 cv. Harper) NIABTAG

Edinburgh (2015-16 cv. Fencer) SRUC

Sclerotinia Stem Rot

(single spray***)

Herefordshire (2015-16 moderate disease) ADAS

*10-20% plants affected followed by 4-10 weeks when similar level of re-infection evident

** Autumn (November/December) followed by pre or early stem extension ((February / March)

***early to mid-flowering application timing

Phoma leaf spot/stem canker and Light Leaf Spot Treatments since 2014

(not all approved for use on vegetables in the UK)

Product Active(s)Full Dose

(l/ha)Phoma

Light Leaf

Spot

Untreated - - + +

Proline 275 prothioconazole 0.63 + +

Prosaro prothioconazole + tebuconazole 1.0 - +

Oriusa tebuconazole 1.25 - +

Refinzarb penthiopyrad + picoxystrobin 1.0 + +

Orius P prochloraz + tebuconazole 1.5 - +

Pictorc dimoxystrobin + boscalid 0.5 + +

Cirkon prochloraz + propiconazole 1.125 + +

Filan boscalid 0.5 (kg/ha) + -

aTested as a 2-spray programme but now one application per season, after GS20/in the spring.bTested as a 2-spray programme but the label restricts use to maximum one application per season

(at full dose) before GS30 (stem extension).cCan only be used after 1st February and GS20.

Phoma fungicides effective during severe epidemics in Cambridgeshire, UK in 2016

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Percentage of full label dose

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Yie

ld (

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Percentage of full label dose

Proline Orius 20EW

Cirkon Pictor

Refinzar

Orius

Orius – no longer

has

autumn/phoma

recommendation

in the UK

The importance of application timing in decreasing light leaf spot severity (80 to 90% control) and protecting yield – Yorkshire, 2015

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Lig

ht

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ot

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eri

ty (

% l

ea

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aff

ect

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)

Percentage of full label rate

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Yie

ld (

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a)

Percentage of full label rate

Prosaro Proline

Orius 20 EW Refinzar

Orius P Pictor

Orius

2.4

2.5

2.6

2.7

2.8

2.9

3.0

3.1

3.2

0% 25% 50% 75% 100%

Yie

ld (

t/h

a)

Percentage of full label dose

Proline Orius 20EW

Pictor Refinzar

Cirkon

Orius

Suboptimal fungicide application timing results in more disease (40 to 60% control) but still yield benefits from controlling this later phase of the disease – Yorkshire, 2016

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Lig

ht

lea

f sp

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eri

ty (

% l

ea

f a

rea

aff

ect

ed

)

Percentage of full label dose

Future challenge in the UK across canola and vegetable crops – light leaf spot resistance to fungicides

• Now no longer reliant on azoles

• Reports of reduced sensitivity to azoles in laboratory tests for light leaf spot in the UK – from vegetables and canola

• Equivalent mutations to those conferring resistance to azoles in Z. tritici (+ novel mutations)

• Determine distribution of these strains and how to manage resistance development

Carter et al., 2014 (Molecular Plant Pathology 15: 513-322)

Variance accounted for = 62.4%0

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1996 1999 2002 2005 2008 2011 2014

Eradicant

Variance accounted for = 43.2%

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1996 1999 2002 2005 2008 2011 2014

% c

on

tro

l Z

.tri

tici

full

lab

el r

ate

Protectant

AHDB Fungicide Performance winter wheat trials – Z. tritici data

Similar mutations causing resistance in light leaf spot (P. brassicae)as Septoria leaf blotch (Z. tritici) of wheat – Z. tritici data below

Integrated control – blackleg and light leaf spot

• Clean seed/seed testing/seed treatment

• Plough crop residues (keep buried)

• Forecasts/risk assessment

• Disease thresholds/crop monitoring

• Fungicides (diversify products and understand efficacy)

• Resistance breeding (long term)

Comprehensive management for seed crops

Blackleg and light leaf spot management in the UK – summary

• Increase in the severity of these two diseases over the last 10 years in the UK

• Cross-infection of both diseases between canola and vegetable crops

• Distance of crops in relation to susceptible crops, crop debris and residue management (keep stubbles buried to prevent air-borne spore production) and seed testing.

• Combination of fungicides, timing and varieties with better resistance to manage diseases effectively and maintain control long term

Thank you