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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
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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.
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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
0
10000
20000
30000
40000
50000
60000
70000
80000
90000
20
00
20
01
20
02
20
03
20
04
20
05
20
06
20
07
20
08
20
09
20
10
20
11
20
12
20
13
20
14
20
15
20
16
Are
a g
row
n (
acr
es)
Brassica vegetable area in the UK
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Brassica vegetable area (acres) in 2015 in the UK – by crop
0
5000
10000
15000
20000
25000
Cauliflower Broccoli Cabbage, Winter Brussels Sprouts Rutabaga and
turnips
Cabbage, Spring Cabbage, Summer
and Autumn
Horticultural statistics, 2015
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Brassica cropping area (acres) in the UK including canola in 2015
-100000
100000
300000
500000
700000
900000
1100000
1300000
1500000
Oilseed rape Cauliflower Broccoli Cabbage,
Winter
Brussels
Sprouts
Swede and
turnips
Cabbage,
Spring
Cabbage,
Summer and
Autumn
Are
a g
row
n (
acr
es)
Horticultural statistics, 2015
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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
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Other diseases affecting brassica vegetables in the UK
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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
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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
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Phoma leaf spot and stem canker (blackleg)
Phoma A = Leptosphaeria maculans Phoma B = Leptosphaeria biglobosa Stem canker
(blackleg)
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Phoma leaf spot epidemics on canola (England and Wales since 2008) – fungicide treated crops
0
10
20
30
40
50
60
November March
Pe
rce
nta
ge o
f p
lan
ts a
ffe
cte
d n
ati
on
ally
2008 2009 2010 2011 2012 2013 2014 2015
Source: DEFRA canola disease survey
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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
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Phoma leaf spot produces air-borne spores under UK conditions
Sep
Jan
Mar
Nov
May
Jul
Phoma leaf spot
Air-borne spores only
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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
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[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
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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.
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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
0
10
20
30
40
50
60
70
80
90
100
2 months 12 months
Duration of burial
Percentage of debris with pseudothecia
Number of pseudothecia per m2
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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
0
20
40
60
80
100
UnploughedPloughed Site 1
Ploughed site 2Ploughed site 3
Ploughed site 4
Dis
tan
ce f
rom
ca
no
la d
eb
ris
(m)
Pe
rce
nta
ge
of
pla
nts
wit
h l
ea
f sp
ot
Site ploughed or unploughed
Proximity to crop debris and development of leaf spot in canola (mid-November)
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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)
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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
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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?
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•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
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Light leaf spot – canola leaves and stems
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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
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Light leaf spot epidemics on canola (levels in the spring in England and Wales since 2008)
0
10
20
30
40
50
60
70
80
90
100
% crops % plants
2006 2007 2008 2009 2010 2011 2012 2013 2014 2015
Source: DEFRA canola disease survey
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Light leaf spot on Brussels sprouts 1983-1985 – more disease in Brussels sprouts grown adjacent to canola fields
0
5
10
15
20
25
30
1983 1984 1985
% p
lan
ts o
r b
utt
on
s a
ffe
cte
d
Leaves adjacent Buttons adjacent Leaves distant Buttons distant
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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
0
10
20
30
40
50
60
70
80
90
100
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)
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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
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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
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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
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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
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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
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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
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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.
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Phoma fungicides effective during severe epidemics in Cambridgeshire, UK in 2016
0
10
20
30
40
50
60
0% 25% 50% 75% 100%
Ca
nk
er
ind
ex
(0
-10
0)
Percentage of full label dose
3.4
3.5
3.6
3.7
3.8
3.9
4.0
4.1
4.2
4.3
4.4
0% 25% 50% 75% 100%
Yie
ld (
t/h
a)
Percentage of full label dose
Proline Orius 20EW
Cirkon Pictor
Refinzar
Orius
Orius – no longer
has
autumn/phoma
recommendation
in the UK
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The importance of application timing in decreasing light leaf spot severity (80 to 90% control) and protecting yield – Yorkshire, 2015
0
2
4
6
8
10
0% 25% 50% 75% 100%
Lig
ht
lea
f sp
ot
sev
eri
ty (
% l
ea
f a
rea
aff
ect
ed
)
Percentage of full label rate
3.2
3.4
3.6
3.8
4.0
4.2
4.4
4.6
4.8
5.0
0% 25% 50% 75% 100%
Yie
ld (
t/h
a)
Percentage of full label rate
Prosaro Proline
Orius 20 EW Refinzar
Orius P Pictor
Orius
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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
2
3
4
5
6
7
8
9
10
11
12
0% 25% 50% 75% 100%
Lig
ht
lea
f sp
ot
sev
eri
ty (
% l
ea
f a
rea
aff
ect
ed
)
Percentage of full label dose
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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)
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Variance accounted for = 62.4%0
10
20
30
40
50
60
70
80
90
100
1996 1999 2002 2005 2008 2011 2014
Eradicant
Variance accounted for = 43.2%
0
10
20
30
40
50
60
70
80
90
100
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
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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
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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
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Thank you