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DEPARTMENT for ENVIRONMENT, FOOD and RURAL AFFAIRS
Research and Development
CSG 15
Final Project Report
(Not to be used for LINK projects)
Two hard copies of this form should be returned to:
Research Policy and International Division, Final Reports Unit
DEFRA, Area 301
Cromwell House, Dean Stanley Street, London, SW1P 3JH.
An electronic version should be e-mailed to [email protected]
Project title
Improved management strategies for diseases of oilseed rape
DEFRA project code
AR0212
Contractor organisation
and location
ADAS Consulting Ltd
Woodthorne
Wergs Road
Wolverhampton
WV6 8TQ
Total DEFRA project costs
Project start date
£ 320991
01/04/99
Project end date
31/03/03
Executive summary (maximum 2 sides A4)
INTRODUCTION AND POLICY RATIONALE
Winter oilseed rape is the most widely-grown break crop in UK arable systems. Despite widespread use of
fungicides, yield losses have been valued at up to £80 million/annum in recent years. Fungicide treatments are
often ineffective because they are either not well-timed or unnecessary. Therefore, improved targeting of
fungicide inputs in oilseed rape addresses both environmental and sustainability aspects of Defra policy. Disease
incidence and severity show marked seasonal and regional variation, which makes decision making complex and
difficult to optimise. Disease resistant cultivars are available but not fully exploited. In addition, the benefits of
disease resistance and agronomic factors for integrated control strategies and the resulting opportunities to reduce
pesticide inputs are poorly quantified. This project (in collaboration with AR0211) focuses on understanding the
interaction between the oilseed plant, fungal pathogens and environmental factors. Two pathosystems have been
investigated :
 stem rot (Sclerotinia sclerotiorum) for which crops are often treated unnecessarily;
 phoma leaf spot and canker (Leptosphaeria maculans) for which fungicide timing is not generally
optimised.
Factors contributing to the management of epidemics of stem canker, light leaf spot and sclerotinia stem rot have
been investigated under field conditions using natural epidemics and by collaborative statistical analyses of
epidemiological data. Observations under field conditions complement laboratory studies in AR0211 and allow
CSG 15 (9/01)
1
Project
title
Improved management strategies for diseases of oilseed rape DEFRA
project code
AR0212
disease epidemics to be modelled as a basis for developing strategic guidance for industry. The exploitatiom of
new fundamental understanding in epidemiology has been taken forward with industry support.
Objective 1. To investigate field and crop factors which favour sticking of petals and host infection by
Sclerotinia sclerotiorum
For sclerotinia, new relationships linking stem rot incidence with weather data and petal inoculum were obtained,
though these differed between years. Studies of petal biology provided understanding of flower development and
petal loss on the primary and secondary racemes. Adjusting seed rates and using apetalous or reduced petal types of
oilseed rape had a small effect on the environment within the crop during flowering. There were few occasions
each year when large numbers of petals stuck to the foliage, but such events are considered an important factor in
epidemic development. Field and laboratory studies indicated that periods of light rain provided good conditions
for petal sticking, whilst heavy rain washed petals off the leaves. Most petal fall occurs after the mid-flowering
stage and collect or stick to leaves at the mid-plant level. Fungicide treatments are likely to be most effective when
applied just prior to the mid-flowering stage. Temperature and rainfall are usually limiting for sclerotinia activity
in the UK, so that air-borne spore inoculum concentrations are low and not well-synchronised with flowering.
Objective 2. To investigate the effects of host plant types and genetic resistance on canker development
Strategies to manage epidemics of stem canker and light leaf spot have been progressed using sites in the east
and north to produce plants of different sizes (from two sowing dates) and evaluate integration of cultivar
resistance with fungicides. Disease progress was monitored on large and small plants to establish if it was
appropriate to have plants which became a large ‘target’ with many phoma leaf spots or a small ‘target’ which
had potential to avoid phoma spotting. Small or late-sown plants produced fewer leaves and retained them
longer than early sown plants and this resulted in a more severe foliar epidemic of phoma leaf spot on small
plants. Leaf production was slightly slower on the later sown plants than on early sown plants and these
relationships have been quantified in thermal time. Fungicides provided better control of epidemics on larger
plants, which also provided greater flexibility for spray application. Moderate and severe cankers were well
controlled with two autumn fungicides though benefits were still apparent from programmes which included
January sprays. There were benefits from cultivar resistance which resulted in more effective control of canker,
but smaller yield responses than on susceptible cultivars. Fungicides gave more effective control of phoma
canker than an increase in canker resistance rating from 5 to 7 (on a 1-9 scale). Yield loss was related to canker
everity and occurred when cankers girdled more than half the stem circumference pre-harvest. Early epidemics
of phoma leaf spot were the most damaging and, conversely, late phoma epidemics had little effect on yield.
Protection of yield can be achieved using resistant cultivars, fungicides and sowing in late August to produce
large plants. The production of plants with 6-7 leaves at the onset of phoma epidemics by early sowing should
provide a valuable component of improved disease management. Datasets have been used in the PASSWORD
project which aims to produce models capable of predicting canker development and yield loss. This computerbased Decision support system will allow management decisions on the use of fungicides to be adjusted in the
light of a cost-benefit analysis. The project has been integrated with HGCA and other industry-funded projects
with synthesis and potential for delivery to users in future through the PASSWORD project.
Technology transfer
Technology transfer has taken place using refereed scientific publications, a book chapter, conferences and
press briefings and has been supported by various sectors of industry.
Conclusions and relevance to policy
This project addresses Defra policy objectives of sustainable production and pesticide minimisation. The impact
of different disease epidemics has been quantified and situations where fungicide treatments are not required
have been identified. There are opportunities to exploit cultivar and crop agronomy so that the risks of diseaseinduced yield losses are reduced. Reduced pesticide applications will improve protection of the public and the
environment. Contributions from this project to the development of forecasting systems for light leaf spot and
CSG 15 (9/01)
2
Project
title
Improved management strategies for diseases of oilseed rape DEFRA
project code
AR0212
phoma canker, now enable farmers and advisers to take a strategic view of disease risks over the whole season.
This will allow more rationale integration of cultivar resistance, crop management and agrochemical usage.
There is a need to improve decision making at the individual crop level and this would be require the
development of rapid diagnostic techniques to quantify primary air-borne spore inoculum. Improved
exploitation of genetic disease resistance also merits further study and this will necessitate investigation of
pathogen variation. Plant size can be considered a disease escape mechanism for phoma canker but other
characteristics should be investigated for light leaf spot and other diseases in oilseed rape.
CSG 15 (9/01)
3
Project
title
Improved management strategies for diseases of oilseed rape DEFRA
project code
AR0212
Scientific report (maximum 20 sides A4)
Scientific objectives
This project had the overall objective of improving risk assessment and integrated control for sclerotinia stem rot and
canker using different ‘model’ plant types. There were two main areas of investigation:
1. To investigate field and crop factors which favour sticking of petals and host infection by Sclerotinia sclerotiorum
1.1 Assess the performance of two oilseed rape types with different risks, e.g. Apex (standard) and a breeding line with
fewer petals (seed to be supplied by The John Innes Centre) grown at two plant densities at two high risk sclerotinia
sites in harvest years 1999, 2000, 2001and 2002.
1.2. Determine the relationship between plant type, and proportion of petals that adhere or fall, and the incidence of stem
rot.
1.3 Relate weather conditions to petal loss, petal adhesion and stem rot disease.
1. To investigate the effects of host plant types and genetic resistance on canker development
2.1 Quantification the effects of leaf size and leaf retention on the development of phoma leaf spot and canker.
2.2 Appraisal of the contribution and value of genetic resistance for the control of phoma leaf spot and canker.
2.3 Examination of disease development in relation to weather factors.
Progress against objectives.
1. Factors affecting Sclerotinia
Different crop densities produced by varying seed rates did not show significant differences in sclerotinia infection. Small
differences in temperature and surface wetness were detected between extreme plant types prior to flowering but
compensatory crop growth resulted in few treatment effects during flowering. In most years, a low incidence of
sclerotinia stem rot occurred on apetalous and reduced petal types and sclerotinia was confirmed on sepals of the
apetalous cultivar. Flower opening and petal fall were quantified on a range of sites and cultivars and relationships were
defined in time and in thermal time. The main period of petal fall occurred after the mid-flowering stage and most petals
were retained on the leaves at the mid-plant level. Lower leaves only persisted for the early stages of flowering and
therefore provided a short-term infection court for sclerotinia. In general, petal loss can be predicted using thermal time.
There were few occasions each season when large numbers of petals adhered strongly to the foliage. This was associated
with rainfall rather than dew and periods of leaf wetness lasting 12-24 hours. Laboratory experiments with detached
leaves and freshly collected petals also indicated that lightly wetted petals and lightly wetted leaves provided the most
favourable conditions for petal sticking. Progress on these objectives now allows flowering and petal fall to be predicted
and provisional criteria for crop infection in relation to rain and surface wetness are available
2. Development of phoma leaf spot and stem canker
Different epidemics of phoma leaf spot and stem canker have been produced and this enabled the effects of cultivar
resistance and plant development to be quantified. Early sown plants showed earlier and more numerous phoma leaf
spotting, but late sown plants eventually showed more severe infection (% leaf area affected) as leaves were smaller and
were retained longer. Early sowing resulted in higher yields and improved disease and weed management. Early phoma
epidemics which start in late September or early October are the most damaging, whilst late epidemics starting in late
November on large plants have little effect on yield. On moderately susceptible cultivars (canker resistance rating 5), the
yield response to fungicides was up to 0.7 t/ha whilst resistant cultivars (canker resistance rating >5) showed responses
up to 0.5 t/ha. There was some evidence of resistance to phoma leaf spot in the foliage, particularly cv. Escort. In
addition, resistance to the canker phase appears to delay the appearance of the stem cankers and this can be quantified in
thermal time. The contribution of cultivar resistance to canker control over the resistance ratings 5 to 7 was smaller than
that obtained from fungicides. Data from the project are being used in the development of models to predict the
development of phoma epidemics and the impact of cultivar resistance and fungicide sprays. The onset of phoma leaf
spotting can be predicted using temperature and rainfall records from mid-July to end of September. The appearance of
stem canker and its effect on yield can now be predicted using thermal time.
CSG 15 (9/01)
4
Project
title
Improved management strategies for diseases of oilseed rape MAFF
project code
AR0212
Methods
1. Sclerotinia
Oilseed rape crops were monitored at different sites from 1999 to 2002 (8 crops in total), primarily to investigate the
effect of environmental conditions on petal sticking (Table 1). From 1999 – 2001, two cvs were used at each site: a
conventional cv. and a reduced-petal cv., drilled at three seed rates to produce different plant densities (range was 30 - 94
plants/m2). In 2002, assessments were carried out in commercial crops close to ADAS Terrington and ADAS
Wolverhampton. The JIC Reduced Petal cv. was obtained originally from Dr. E. Arthur, John Innes Institute in 1999.
Seed from the Reduced Petal crop harvested in 1999 was used for the 1999/2000 and the 2000/2001 trials. Each trial was
set up as a two-way factorial (cultivar x seed rate), in a randomised block design with four replicate plots of each
treatment. Both cultivars were sown at three densities (seed rates 60, 90 and 120 /m2, referred to as low, mid and high,
respectively); cvs. Apex or Hyola had fungicide treated and untreated plots but cv. Reduced Petal had only untreated
plots. A standard fungicide treatment (iprodione + thiophanate methyl/carbendazim) was applied at early flowering to
the appropriate Apex or Hyola plots.
Table 1. Sites and oilseed rape cultivars in sclerotinia experiments, 1999 – 2002.
Harvest year
Site
cv. 1
cv. 2
Crowland, Lincs
Winter/
spring
Spring
1999
Hyola 401
ZNA
(apetalous)
1999
Syerscote, Staffs
Winter
Apex
Pronto
2000
Syerscote, Staffs
Winter
Apex
JIC reduced
petal
2001
Terrington, Norfolk
Winter
Apex
JIC reduced
petal
2001
Syerscote, Staffs
Winter
*Apex
JIC reduced
petal
2001
Boningale, Wolves
Winter
**Contact
-
2002
Boningale, Wolves
Winter
**Fortress
-
2002
Terrington, Norfolk
Winter
**Escort
-
*Reduced assessments due to restricted access to site during Foot & Mouth epidemic.
**Commercial crop, one cv. only.
Plant counts were recorded in five 50 cm x 50 cm (0.25 m2) quadrats in all untreated plots in March or immediately after
harvest. At mid- to late flowering, counts were made of the number of flowering racemes on 5 randomly selected plants
in all untreated plots. The number of newly-opened flowers, total flowers open on the day and the number of flowers lost
since the last assessment were counted on the main raceme of 5 - 10 plants per plot. Counts were made frequently, daily
if possible, from the start to finish of flowering on the main racemes. A record of flowering progress on secondary
racemes was made over the same period. Growth stages were recorded using the key produced by Sylvester-Bradley and
Makepeace (1984) on 5 plants/monitored plot throughout flowering.
The extent of petal fall was assessed throughout flowering. Crops were usually monitored three times each week and daily
where possible, to establish when petals had stuck to the foliage. Five plants per plot were randomly selected from each
of three replicates from across untreated, medium seed rate plots of cvs Apex or Hyola. One leaf from each of the
bottom, middle and top regions of the stem (measured from the ground to the base of the main raceme) was selected and
tagged so that the same leaf could be assessed on all assessments. Petals were also counted in trays (550 cm2) placed on
5
Project
title
Improved management strategies for diseases of oilseed rape MAFF
project code
AR0212
the ground, to monitor the pattern of total petal fall during flowering. Petal stick was tested by up-turning leaves with
petals on them and counting those that remained on the leaf. A ‘stick event’ was defined as a mean of >2 petals sticking
per leaf. On each leaf, the following assessments were done: the total number of petals (one plant per plot only), the
number of new and old sticking petals present, the % leaf area covered by the new and old sticking petals. In the axils,
the number of new and old sticking petals present were counted.
On at least three occasions, early, mid- and late flowering of main racemes, petals were cultured on agar. Ten racemes
were collected in total from each of the two varieties from the middle seed rate untreated plots. There were sufficient
petals to sample from the Reduced Petal cv. One petal was selected from each of four flowers per raceme. Petals were
collected in a spiral pattern from the newest fully open petals near the top of the raceme down to the oldest intact petals
near the bottom of the raceme. The four petals from each raceme were placed onto a plate containing PDA amended with
streptomycin. The plates were incubated at 20ºC and assessed after 7-10 days for the presence of S. sclerotiorum.
Immediately prior to harvest, sclerotinia stem rot lesions were recorded on a whole plot basis, i.e. all plants showing stem
rot lesions were recorded from each plot. The location of lesions was recorded as low, middle or high. Yield was assessed
at harvest. All replicated data were subjected to analysis of variance. Treatment means were separated using SEDs where
the variance ratio was significant (P 0.05).
Meteorological data were collected on a weekly basis from early March until early July using a Delta-T Logger. Where
possible, air temperature and relative humidity at two positions in a medium seed rate plot of each variety, rainfall, wind
speed, leaf wetness at three positions (bottom, middle and top) in a medium seed rate plot of each variety and soil temperature
at 2 cm were recorded every 10 minutes.
In 2002, a laboratory experiment was carried out to investigate the factors which affected petal sticking to leaves. Leaves
and petals were collected from a field crop and two petals were placed on each of five detached leaves in each replicate of
a randomised block design. Dry, lightly misted or wet petals were placed on dry leaves, dry or misted petals on misted
leaves and dry or wet petals on wet leaves. Treatments were carried out with both the inner surface and the outer surface
of the petals in contact with the upper surface of the leaves. After drying under ambient conditions for 24 h, petal sticking
was assessed by recording the percentage contact with the leaf surface and how firmly the petal adhered to the leaf (0-4
index).
2. Host plant types and genetic resistance for canker control
2.1 Sow date, seed rate and fungicide interactions
Table 2 Sow dates, fungicide timing and onset of phoma leaf spotting in Time of Sowing experiments, 1999-2001.
Site
Year
Sow date
Early
Late
Fungicide
Autumn 1
Autumn 2
Spring 1
Spring 2
Epidemic
onset
GS at
Phoma
onset
1999
Boxworth
2000
2001
1999
High Mowthorpe
2000
2001
3 Sep
22 Sep
31 Aug
22 Sep
21 Aug
11 Sep
7 Sep
17 Sep
27 Aug
10 Sep
30 Aug
24 Sep
20 Oct
2 Dec
21 Jan
9 Mar
28 Oct
29 Nov
14 Jan
22 Feb
6 Nov
18 Dec
16 Jan
5 Mar
6 Nov
9 Dec
18 Feb
21 Apr
9 Nov
17 Jan
22 Feb
31 Mar
14 Nov
5 Jan
9 Feb
14 Mar
14 Oct /
26 Oct
1,04 /
1,03
22 Oct /
26 Oct
1,03 /
1,03
25 Sep /
17 Oct
1,05 /
1,04
26 Oct
26 Oct / 9
Nov
1,04 /
1,03
2 Oct / 30
Oct
1,04 / 1,02
1,03
6
Project
title
Improved management strategies for diseases of oilseed rape MAFF
project code
AR0212
Six experiments to investigate the interaction of plant size and canker were carried out using the hybrid cv. Pronto at two
sowing dates and two seed rates at ADAS Boxworth and ADAS High Mowthorpe during 1999-2001 (Table 2). The aim
was to produce large plants, which were likely to be affected by many lesions, and contrasting small plants, which
provided a small target. Early-sown plots were drilled in late August or early September and late sown plots were drilled
2-3 weeks later. Target plant populations of 20-25 and 80-100 plants/m2 were used to establish if competition between
plants affected progress of disease epidemics. The seed rate x sow date factors where combined in a factorial design with
fungicide treatments (nil, autumn only, winter only and autumn + winter fungicide programmes of flusilazole +
carbendazim) to improve understanding of disease management in relation to epidemic development. Disease assessments
were carried out from disease onset in autumn at 4-6 week intevals up to harvest, and recorded the incidence and severity
of leaf, stem and pod diseases. Detailed observations on the development of phoma leaf spot were carried out on tagged
untreated plants during the autumn and winter to monitor the incidence and severity of phoma spotting on individual leaf
layers. These records enabled the production and loss of leaves to be quantified. The plots were combine harvested and
yields adjusted to 90% dry matter.
2.2 Cultivar resistance and fungicide effects
Cultivar x fungicide interactions were investigated in a total of eight replicated small plot field experiments during 19992002 using natural epidemics of disease at ADAS Boxworth (high canker risk) and ADAS High Mowthorpe (moderate
canker risk and moderate to high light leaf spot risk). Cvs Pronto (canker resistance rating 5) and Apex (canker resistance
rating 6) were used as standards in all experiments, whilst more resistant cvs Licrown, Escort and Lutin were included
according to availability (canker resistance rating 7) (Table 3). Fungicide regimes based on flusilazole + carbendazim
were applied in autumn/early winter or winter/spring as two-spray programmes or on all dates to test the hypothesis that
only early canker infection has a significant effect on yield. Disease assessments were carried out from disease onset in
autumn at 4-6 week intervals up to harvest and recorded the incidence and severity of leaf, stem and pod diseases. The
plots were combine harvested and yields adjusted to 90% dry matter.
Table 3. Date of sowing, onset of phoma leaf spotting and cultivars in Cultivar x Fungicide experiments, 1999-2002.
Site
Year
1999
Boxworth
2000
2001
2002
1999
High Mowthorpe
2000
2001
2002
7 Sep
31 Aug
1 Sep
30 Aug
7 Sep
27 Aug
30 Aug
31 Aug
Alpine
Apex
Licrown
Pronto
Alpine
Apex
Licrown
Pronto
Contact
Pronto
Apex
Escort
Lutin
Pronto
Apex
Escort
Alpine
Apex
Licrown
Pronto
Alpine
Apex
Licrown
Pronto
Contact
Pronto
Apex
Escort
Lutin
Pronto
Apex
Escort
20 Oct
1 Dec
21 Jan
9 Mar
27 Oct
29 Nov
17 Jan
22 Feb
14 Nov
13 Dec
17 Jan
5 Mar
17 Oct
30 Nov
9 Jan
15 Mar
6 Nov
9 Dec
18 Feb
21 Apr
9 Nov
17 Jan
22 Feb
31 Mar
14 Nov
5 Jan
9 Feb
14 Mar
1 Nov
10 Dec
8 Feb
19 Mar
Epidemic
onset
20 Oct
27 Oct
14 Nov
13 Oct
26 Oct
26 Oct
12 Oct
1 Nov
GS at
phoma
onset
1,07
1,03
1,12
1,04
1,03
1,04
1,04
1,07
Sowing
date
Cultivars
Fungicide
Autumn 1
Autumn 2
Spring 1
Spring 2
7
Project
title
Improved management strategies for diseases of oilseed rape MAFF
project code
AR0212
Results
1. Sclerotinia
1.1 Assess the performance of two oilseed rape types with different risks and a breeding line with fewer petals, grown at
two plant densities at two high risk sclerotinia sites in harvest years 1999, 2000 & 2001.
Varying seed rate had little effect on yield in winter oilseed rape, but there was a response to increasing seed rate on spring
oilseed rape in 1999 (Table 2). However, there were small but significant differences in yield between cultivars in four out
of five experiments. Overall, stem rot incidence was low except in 1999 at Syerscote and had little effect on yield.
Table 4. Yield in untreated plots of oilseed rape in relation to seed rate, 1999 – 2001.
Seed rate
Year
Site
cv. 1
Low
Mid
Seed rate
High
cv. 2
Low
Mid
High
SED
SED
SED
Seed
Cv.
SR.x Cv
rate
1999
Lincs
Hyola
1.2
1.8
2.1
401
ZNA
0.7
1.2
1.1
0.16*
0.13*
0.23
(Apet.)
1999
Staffs
Apex
3.6
3.8
3.7
Pronto
4.0
4.1
4.1
0.13
0.10*
0.18
2000
Staffs
Apex
4.5
4.1
4.2
JIC
3.2
2.6
2.4
0.28
0.23*
0.40
2001
Norfolk
Apex
4.3
4.2
4.3
JIC
3.8
4.1
3.8
0.18
0.14*
0.25
2001
Staffs
Apex
2.4
2.1
2.3
JIC
2.1
2.2
2.1
0.10
0.08
0.15
* = Significant difference (P<0.05). Apet. = apetalous
Sclerotinia stem rot and petal infection
Petal infection as determined by agar plate tests was low at most sample times, and did not correlate well to final stem rot
levels (Table 5). The highest recorded petal infection values were 47.5% at mid-flower on cv. Apex, Staffordshire 2001
(2% stem rot), and 43% at mid-flower on cv. Hyola 401, Lincolnshire 1999 (<1% stem rot). In most years, stem rot was
low, with 6% or less plant infection. The exception was Staffordshire, 1999, with 27% and 32% stem rot in Apex and
Pronto, respectively, but petal infection was not detected in any of the samples at this site. This 1999 experiment gave the
clearest indication that seed rate had no significant effect on stem rot development. The apetalous cv. ZNA drilled in
Lincolnshire in 1999, had very few petals, but sepals were recorded sticking on the leaves. The sepals were found to have
up to 39% infection with sclerotinia, but no stem rot developed in that year on either ZNA or conventional petal type cv.
Hyola 401. The reduced-petal cultivar gave some crinkled petals and slight reductions in petal number, but provided a
limited contrast with conventional cultivars, especially in the second and third year of the project. When leaves of cv.
Apex were artificially inoculated with sclerotinia mycelium during flowering at experimental sites, stem lesions usually
appeared 14 to 16 days later. This confirmed that environmental conditions were not limiting disease development if
appropriate inoculum was present.
8
Project
title
Improved management strategies for diseases of oilseed rape MAFF
project code
AR0212
Table 5. Sclerotinia stem rot incidence and % petals at early, mid- and late flowering with sclerotinia infection on main
raceme, 1999-2002.
Year
cv. 1
Stem
rot %
Early
%
petal
inf.
Mid
%
petal
inf.
Late
%
petal
inf.
cv. 2
Stem
rot %
Early
%
petal
inf.
Mid
%
petal
inf.
Late
%
petal
inf.
1999
Hyola 401
<1
-
43.0
34.0
ZNA
(apet.)
<1
-
39.0*
23.0*
1999
Apex
26.9
0
0
0
Pronto
31.8
0
0
0
2000
Apex
3.0
0
7.5
10
JIC
6.0
0
5.0
7.5
2001
Apex
<1
2.5
2.5
0
JIC
<1
15
2.5
2.5
2001
Apex
2.0
22.5
47.5
32.5
JIC
2.0
**
**
**
2001
Contact
0
0
5
10
-
-
-
-
-
2002
Fortress
8.0
18.0
21.0
5.0
-
-
-
-
-
2002 Escort
0
1.9
0.6
1.9
*Sepals tested (instead of petals) on apetalous cv. Inf. = infection. Apet. = apetalous.
**Not done; resources diverted to cv. Contact site 2001 due to Foot & Mouth problems.
-
Within crop environments in different cultivars
The truly apetalous spring cv. ZNA showed no differences in temperature at mid-canopy height when compared to full
petal Hyola at the same seed rate. However, there was up to 30% less leaf wetness duration on cv. ZNA than on cv.
Hyola at ground level and at mid-canopy height throughout flowering. Small differences in temperature were recorded
between different seed rates prior to early flowering using sensors positioned at different heights in the crop canopy. At
Syerscote in 2000, for example, temperatures at mid-plant height in the low seed rate Reduced Petal cultivar were up to
2oC higher than at the same plant height in the high seed rate of cv. Apex. (Fig. 1). However, after GS 4.7, air
temperatures were similar at each seed rate and leaf height. There were no consistent differences in leaf wetness duration
at different heights in the canopy, but some evidence that, during periods of low or no rainfall, the leaves at the bottom of
the canopy stayed wet for longer than the upper leaves. The lower numbers of petals on the reduced-petal cultivar had
little effect on temperature and surface wetness. In all years, where three seed rates were used, there were significant
differences between the numbers of plants established, which gave a 2-3 fold variation in plant populations (Table 4).
However, compensatory growth in the spring resulted in similar numbers of racemes during flowering in all seed rates,
except for 2000 where there were significantly more racemes in the low seed rate treatments.
1.2. Determine the relationship between plant type, and proportion of petals that adhere or fall, and the incidence of stem
rot.
Progress of flower opening and petal fall
On all cultivars, except the apetalous ZNA, flowers opened and accumulated on the main raceme until about half the
buds were open (GS 4,5) and then petal fall commenced. At Terrington in 2001, for example, petal fall began 7-11 days
after the start of flower opening, 50% of flowers were open 9 - 13 days after the onset of flowering and flowers lasted 4-6
days. The main petal fall occurred from the mid-flowering stage onwards. In all years and with all cvs, the overall rate of
flower opening was often faster than the rate of flower loss (as shown by linear regressions fitted to data with time
9
Project
title
Improved management strategies for diseases of oilseed rape MAFF
project code
AR0212
variable in days (Table 6). Plotting flower progress on thermal time (day degrees accumulated above 0oC) gave the same
relationship as for time between flower opening and flower loss (Table 7). There were slight differences between sites for
flower development which were greater than cultivar differences.
Fig. 1. Effect of seed rate and plants with reduced petals on the air temperature within the crop canopy.
20
15
o
C
10
Reduced Petal
Max
Apex
Mean
Reduced petal
Apex
Apex
5
Min
Reduced petal
0
22-Apr 23-Apr 24-Apr 25-Apr 26-Apr 27-Apr 28-Apr 29-Apr 30-Apr
01May
02May
03May
04May
05May
Table 6. Regression equations for winter oilseed rape flower opening and flower loss in real time.
Year
Site
2000
2001
2001
2001
Wolverhampton
Wolverhampton
Terrington
Terrington
Cv.
Flower opening
Y
= % flowers open,
x =time in days
Y=2.27x+7.95
Y=3.98x+9.61
Y=3.62x+8.85
Y=3.70x+3.80
Apex
Contact
Apex
JIC Red.
Petal
2002 Wolverhampton
Fortress
Y=2.09+27.94
2002 Terrington
Escort
Y=2.65x+11.42
*R2 = Percentage variance accounted for.
*R2
*R2
0.96
0.91
0.93
0.94
Flower loss
Y = % flowers with
fallen petals,
x =time in days
Y=2.49x-18.7
Y=4.46x-11.97
Y=3.93x-15.80
Y=3.72x-16.50
0.78
0.87
Y=2.78x-2.91
Y=3.09x-12.45
0.88
0.93
0.90
0.95
0.93
0.93
Table 7. Regression equations for winter oilseeD rape flower opening and flower loss in thermal time (degree days).
Year
Site
2000
2001
2001
2001
Wolverhampton
Wolverhampton
Terrington
Terrington
Cv.
Flower opening
Y = % flowers
open,
x = thermal time
in dgree days
Y=0.24x+12.30
Y=0.32x+4.11
Y=0.31x+13.14
Y=0.31x+8.14
Apex
Contact
Apex
JIC Red.
Petal
2002 Wolverhampton
Fortress
Y=0.21x+35.75
2002 Terrington
Escort
Y=0.26x+18.57
2
*R = Percentage variance accounted for.
10
*R2
*R2
0.94
0.89
0.91
0.93
Flower loss
Y = % flowers with
fallen petals,
x = thermal time in
dgree days
Y=0.27x-15.35
Y=0.36x-18.3
Y=0.34x-12.13
Y=0.32x-13.15
0.70
0.83
Y=0.28x+6.29
Y=0.31x-4.66
0.84
0.90
0.91
0.93
0.95
0.95
Improved management strategies for diseases of oilseed rape MAFF
Project
title
project code
AR0212
Petals were caught by leaves or leaf axils at all positions in the crop canopy (typically 0-8 petals/leaf and 0-2 petals/axil),
but the highest numbers were trapped at the upper and mid-leaf level (e.g., Wolverhampton 2002, Fig. 2), with most
petals caught by the larger leaves at the mid-canopy level. Lower leaves senesced and were lost as flowering progressed
so that the middle and upper leaves provided the main sites for petal retention and for stem infection. In a few of the
Assessments, increased petal retention on leaves was associated with higher seed rates, but this was not consistent across
sites and years. There were insufficient differences between flower and petal numbers on the JIC Reduced Petal cv. and
Apex to show differences in the number of petals caught on leaves between the two cvs. Petal fall as recorded in trays
generally preceded or coincided with peaks of petals fallen or stuck onto leaves and axils (Fig. 2). The main peak of
petal fall occurred after 100% of main racemes were flowering (Fig. 2), which indicated that petals from later flowering
secondary racemes could also be important infection routes for sclerotinia. Petal stick was never observed on leaves
before GS 4,5. As with petal fall, the greatest number of total petals caught on leaves, and also the number of newly stuck
petals, were observed during and after the time at which 100% of racemes (main and secondary) were flowering.
1.3 Relate weather conditions to petal loss, petal adhesion and stem rot disease.
Fig. 2. Number of petals caughton leaves of winter oilseed rape, % of racemes in flower and number of petals caught in
ground trays, Boningale, Wolverhampton, 2002.
120
6
Petals on
leaves
5
% of racemes
flowering
100
80
Petals in trays
4
60
3
40
% racemes flowering;
no. of petals in trays
Number of petals
caught on leaves
7
2
20
0
0
0 6-A
pr
0 8-A
pr
1 0-A
pr
1 2-A
pr
1 4-A
pr
1 6-A
pr
1 8-A
pr
2 0-A
pr
2 2-A
pr
2 4-A
pr
2 6-A
pr
2 8-A
pr
3 0-A
pr
0 2-M
ay
0 4-M
ay
0 6-M
ay
0 8-M
ay
1 0-M
ay
1 2-M
ay
1 4-M
ay
1 6-M
ay
1 8-M
ay
2 0-M
ay
2 2-M
ay
2 4-M
ay
1
Environmental effects and petal stick in the field
Falling petals failed to stick to leaves when there was no rainfall in the 24 hours before assessment. During these periods,
leaf wetness was usually due to dew (see 24-25 April data in Fig. 3) and confined to late night and early morning. When
petals did stick to leaves, leaf wetness had generally been observed during the previous day. The change from ‘no stick’
to ‘petal stick’ between two consecutive daily assessments was almost always associated with a rainfall event, even if
small, and also with periods of continuous (c. 12-24 h.) leaf wetness (see rain and petal sticking data for 26 April in Fig.
3). Short periods of leaf wetness did not appear to result in petals sticking to the leaves. Heavy rain did, however, wash
stuck petals off leaves, e.g. at Terrington in 2002, when it was noted that 8.3 mm rain over 9 hours immediately prior to
assessment, had washed off at least 50% of the ‘old’ stuck petals.
The number of major petal sticking ‘events’, when 5 or more petals were found stuck on tagged leaves, only occurred on
two or three occasions each season. From 1999 to 2001, at both the east and Midlands sites, there were two or three
periods when petal stick events occurred, all at GS 4.6 or later. In 2002, at both the east and Midlands sites, there were
rather more periods of wet weather when petals were either continuously stuck or new petal sticking took place, e.g., at
11
Project
title
Improved management strategies for diseases of oilseed rape MAFF
project code
AR0212
Boningale, sticking was recorded on 15, 18, 19, 26-30 April, 1, 13-15 and 20-24 May. A similar pattern occurred at
Terrington in 2002.
6
5
4
3
2
1
26-A
pr 24
00
26-A
pr 12
00
25-A
pr 24
00
25-A
pr 12
00
0
% of hour leaf wet
Hourly rainfall (mm)
Total petals caught
O ld stuck petals
N ew stuck petals
W ind speed (m/s)
Rain (mm), wind (m s -1 ), no of pe tals
100
90
80
70
60
50
40
30
20
10
0
24-A
pr 24
00
% of hour with le af we t
Fig. 3. Petal sticking and environmental conditions, Wolverhampton 2002.
Laboratory studies on petal sticking
Experiments with detached leaves and freshly collected petals showed that the combination of lightly misted petals on
lightly misted leaves gave the highest petal contact (64%) and the strongest petal sticking. Other treatments gave 19-38%
petal contact with leaves and few significant differences, a notable exception being misted petals on dry leaves (38%
contact) which gave better petal contact than wet petals on dry leaves (19% contact). There were some significant
differences between the inner and outer petal surfaces with petals sticking more firmly when the inner surface was in
contact with the leaf surface. Water-soaked petals lost their structure and became folded, reducing the area in contact with
leaf surfaces. The results suggest that light rain, sufficient to moisten both petals and leaves, favoured petal sticking.
However, petals are readily washed off leaves whilst surfaces are wet, and drying conditions at the end of light rain are
important to enable petals to stick. The presence of dew overnight does not generally lead to petal sticking, though this
may be linked to low wind speed and hence low petal fall when dew is present.
Use of petal testing and weather to improve decision making for sclerotinia control
Data from agar petal tests carried out at early, mid- and late flowering in 300 winter oilseed rape crops sampled during
1993-1998 have been examined to establish factors which could be used to improve spray decisions. The initial regression
analysis was confined to the relationship between stem rot and % petals infected by sclerotinia (at early, mid- and late
flower) only. The regression equation for all data, all years combined was: % stem rot = 0.15 early petal infection +
0.086 late petal infection + ai year, where ai = values for 1993, 1994, 1995, 1996, 1997 and 1998, which were 0, 1.11,
4.48, -0.34, 3.73 and 1.74, respectively. The percentage fit was 25.9%. Incorporating farm risk into this analysis did not
improve the relationship. Local weekly weather data, stem rot incidence data for an untreated area in each sampled crop
and previous stem rot history on the farm were then used in a canonical variate analysis. The percentage variance
accounted for each year ranged from 33 to 67%. The best fit models were achieved in the two years in which the highest
stem rot levels were observed: 1995, R2=67%, stem rot 5.1%, and 1997, R2=61%, stem rot 2.9%. Petal infection was still
the most important factor relating to stem rot in 5 out of the 6 years. The relative importance of each weather factor was
different in each year. The mean stem rot levels in each year (SE in brackets) were: 1993, 3.43 (1.33); 1994, 4.42 (1.5);
1995, 5.14 (SE 1.8); 1996, 0.50 (0.25); 1997, 2.9 (0.87); and 1998, 0.97 (0.26). An overall model fitted across all six
years accounted for only 26% of the variance.
12
Project
title
Improved management strategies for diseases of oilseed rape MAFF
project code
AR0212
2. Host plant types and genetic resistance for canker control
2.1 Sow date, seed rate and fungicide interactions
There were significant yield benefits from early sowing in five of the six experiments (Table 8) and the mean advantage
of early sowing was 0.71 t/ha. Seed rate effects were also significant at five out of six sites, with the higher yield being
produced by the high seed rate at four sites. The mean response to the high seed rate was 0.49 t/ha. Fungicides only gave
significant yield responses at High Mowthorpe in 2000 and 2001 and this was to the full programme in 2000 and all
treatments in 2001. There was an overall response to fungicides of 0.18 t/ha from both autumn and spring programmes
and 0.32 t/ha from the full programme. There was also a seed rate x sow date interaction as there was a larger response to
seed rate at the late sowing date (0.64 t/ha compared with 0.32 t/ha at early sowing)
Table 8. Effects of sowing date and seed rate on yield 1999-2001.
Site
Year
1999
Boxworth
2000
2001
High Mowthorpe
2000
2001
1999
Mean
Sow date
Early
Late
SED
CV%
F pr
2.83
1.79
0.120
20.8
<0.001
3.42
3.21
0.058
7.0
0.001
1.79
1.79
0.141
31.6
0.993
3.34
2.49
0.081
11.1
<0.001
4.63
3.22
0.117
11.9
<0.001
3.48
2.82
0.141
17.9
<0.001
3.26
2.55
0.059
Seedrate
Low
High
SED
CV%
F pr
2.15
2.48
0.120
20.8
0.101
3.39
3.25
0.058
7.0
0.020
1.58
1.99
0.141
31.6
0.006
2.41
3.42
0.081
11.1
<0.001
3.45
4.40
0.117
11.9
<0.001
2.99
3.30
0.141
17.9
0.033
2.66
3.15
0.059
3.23
3.30
3.34
3.38
0.083
7.0
0.320
0.738
45
1.83
1.82
1.72
1.78
0.200
31.6
0.956
0.490
44
2.85
2.79
3.08
2.94
0.114
11.1
0.088
0.267
44
3.72
3.98
3.82
4.18
0.165
11.9
0.039
0.709
45
2.62
3.20
3.21
3.56
0.200
17.9
<0.001
0.102
42
2.73
2.91
2.91
3.05
0.083
Fungicide
Nil
2.08
Autumn
2.39
Spring
2.31
Full
2.47
SED
0.1702
CV%
20.8
F pr
0.127
Interaction F
0.630
DF
45
* Seed rate x sow date.
<0.001
<0.001
0.001
0.007*
340
The largest differences in plant size and in treament effects were obtained at Boxworth in 1998/99 and High Mowthorpe
in 1999/2000. Dry conditions in subsequent years delayed germination and resulted in small differences in plant
development between sow dates particularly at Boxworth. Later sown plants produced fewer leaves and these were
retained longer by the plant than on early sown plants (Fig. 4 ). New leaves were produced at aproximately 100 degree
day intervals and the rate of leaf production was slightly lower in late sown plots. The number of phoma leaf spots per
plant was higher on early sown plants, but the percentage leaf area affected was eventually greater on late sown plants.
There were some effects of seed rate on disease, but these were smaller than the sow date effects. In 1998/99 at
Boxworth, many tagged plants in the late sowing developed severe canker and 74% and had disappeared (cf. only 2%
early sown) before harvest. The final canker indices of 79 for untreated early sown plants, therefore, reflected the full
impact of canker on the early sown plants, whereas an index of 59 for late sown plants did not provide an accurate
measurement of disease because severely affected plants had died well before harvest. Untreated yield data identified the
benefits of early sowing with 3.24 t/ha from early sown treatments and 2.04 t/ha from the late sowing. Seed rate and
fungicide did not produce significant benefits despite significant effects of fungicides on canker severity. Plots with early
13
Project
title
Improved management strategies for diseases of oilseed rape MAFF
project code
AR0212
sowing and higher plant populations were less prone to competitive weed problems and this is a further practical
advantage for crop management.
Table 9. Canker Indices pre-harvest in Time of Sowing experiments 1999-2001.
Site
Year
1999
Boxworth
2000
2001
1999
High Mowthorpe
2000
2001
Mean
Sow date
Early
Late
SED
F prob
50.0
37.9
8.01
0.136
14.6
13.8
1.182
0.529
24.4
18.2
1.473
<0.001
15.1
19.7
2.96
0.126
2.6
3.1
0.787
0.581
9.7
17.7
2.02
<0.001
19.40
18.39
Seed rate
Low
High
SED
F prob
37.9
50.0
8.01
0.136
13.0
15.4
1.182
0.051
18.1
24.6
1.473
<0.001
17.8
17.0
2.96
0.773
3.1
2.6
0.787
0.581
14.5
12.9
2.02
0.443
17.39
20.42
Fungicide
Nil
Autumn
Spring
Full
SED
F prob
Inter F
DF
74.8
40.6
39.8
20.6
11.33
<0.001
0.935
45
28.6
17.1
9.0
2.2
1.672
<0.001
0.480
45
37.0
17.8
23.2
7.3
2.083
<0.001
0.038
43
21.4
20.6
16.6
10.9
4.18
0.062
0.671
45
5.6
0.3
4.3
1.3
1.114
<0.001
0.424
45
28.6
4.7
19.6
2.1
2.86
<0.001
0.797
45
32.66
16.84
18.75
7.39
At High Mowthorpe, early sowings produced consistently higher yields (0.66-1.41 t/ha) than late sown treatments and
there were large benefits from the higher seed rate (c. 1 t/ha) in two years out of three (Table 8). Early sowing increased
light leaf spot and alternaria; however, the severity of these diseases was generally low and unlikely to have had a
significant effect on yield. Late sown plots established poorly at High Mowthorpe and yield effects were explained
through the low seed rate treatment giving sub-optimal plant populations rather than disease interactions.
The severity of canker at Boxworth was only significantly higher in early sown plants in 2001, the only year to show a
significant effect of seed rate (canker more severe at the higher seed rate). There was significant control of canker from all
three fungicide treatments in all three years (Table 9). The full fungicide programme gave the best control of canker and
this was significantly better control than the two-spray treatments in 2000 and 2001. The two-spray programmes did not
control canker very effectively in 1999 and treated plots in that year had more severe canker than the untreated plots in
2000 and 2001. The limited control in 1999 and the relatively low canker indices in 2000 and 2001 accounted for the
absence of significant yield responses to fungicides at Boxworth.
Cultivar resistance and fungicide interacrions
There were no significant differences in yield between treatments in 1999, but cultivar differences were significant during
2000-2002. Fungicide treatments gave significant responses in 2001and 2002 at Boxworth and in 2000-2002 at High
Mowthorpe (Table 10 ). There was no consistent yield benefit from using canker resistant cultivars such as Escort or
Licrown compared with susceptible Pronto and there were no significant cultivar x fungicide interactions. At sites with
significant fungicide responses, there were higher yields from autumn sprays than winter sprays at Boxworth (mean 0.20
t/ha) and High Mowthorpe (0.13 t/ha), but no additional advantage from using a four -spray programme. Mean yield
responses to fungicides across all sites and years were 0.32 t/ha in autumn, 0.28 t/ha in winter and 0.36 t/ha from autumn
and winter programmes. The rather more consistent yield responses at High Mowthorpe (0.46- 0.79 t/ha) compared with
Boxworth reflect a higher incidence (and control ) of light leaf spot.
14
Project
title
Improved management strategies for diseases of oilseed rape MAFF
project code
AR0212
Fig. 4. Leaf production and leaf loss in early and late sown plants, Boxworth 1998/99.
20
18
16
Leaf number
14
12
Early gain
Early lo s s
10
Late gain
8
Late lo s s
6
4
2
0
0
200
400
600
800
1000
1200
1400
The rm a l tim e fro m drilling
At Boxworth, moderate or severe canker developed each year and most of this was controlled by the autumn fungicide
regime with limited effects from winter sprays. In 2001, there was 30% moderate/severe canker at Boxworth, which was
reduced to 3% by the autumn sprays, 17% by the winter sprays and 2% by the full programme. Only the autumn sprays
gave a significant yield response at Boxworth (0.33 t/ha), but all treatments increased yield at High Mowthorpe from 2.56
t/ha to 3.35 (aut.), 3.32 (full) and 3.11 t/ha (spring). Light leaf spot was present on leaves of 71% plants at the end of
flowering at High Mowthorpe and was well controlled (>90%) by all the fungicide regimes. Results in 2002 further
assisted the identification of appropriate fungicide strategies. At High Mowthorpe, the first fungicide spray was applied
on 1 November at GS 1,07 when phoma leaf spot started to develop. Little canker developed by harvest and light leaf spot
was controlled by all the fungicide regimes, which gave similar yield responses (0.42 t/ha autumn, 0.46 t/ha winter and
0.33 t/ha full). Phoma developed rapidly in mid-October at Boxworth when plants were smaller (GS 1,05) although they
subsequently grew rapidly. Autumn sprays reduced the proportion of moderate and severe canker more effectively than
spring sprays. Cultivar resistance provided only partial control of canker as untreated canker indices on cvs Pronto, Apex
and Escort were 73, 55 and 58 respectively. Autumn fungicides gave indices of 40, 25 and 21 on cvs Pronto, Apex and
Escort demonstrating that good disease resistance combined with fungicides provided the lowest disease severity. These
results provided further evidence that plant size at epidemic onset should be a key factor in deciding the crop management
strategy. Where plants have reached the 6-7 leaf stage when phoma spotting develops, there is some fexibility in spray
timing and effective disease control can be achieved with fungicides. Yield responses and the efficacy of disease control
is affected by cultivar resistance and, using cv. Escort as an example, this equated to 0.1 t/ha per point on the resistance
rating scales for stem canker and light leaf spot. There are differences in yield response between the east and north for
phoma control, which relate to the timing and severity of epidemics. On large plants in the north, phoma may cause little
loss of yield after November.
2.3 Disease development and weather factors
New and historic data have been examined to quantify the erffects of rainfall and temperature on the development of
phoma leaf spot and canker. New model relationships have been defined using datasets from other projects and these will
be available through the PASSWORD project (LK0917). Models will predict when 10% plants have phoma leaf spot
from post-harvest rainfall and maximum temperature data and then predict canker development in relation to cultivar
resistance using accumulated mean temperature. This will enable potential yield loss to be defined at disease onset,
providing signifiacnt new guidance on targeting fungicides.
15
Project
title
Improved management strategies for diseases of oilseed rape MAFF
project code
Table 10. Yield in cultivar x fungicide experiments 1999-2002.
Site
Year
1999
Boxworth
2000
2001
2002
High Mowthorpe
2000
2001
1999
2002
Mean
Variety
Pronto
Apex
Alpine
Contact
Escort
Licrown
Lutin
SED
CV%
F pr
2.81
2.88
2.63
3.95
4.09
3.82
3.76
3.48
3.28
3.99
3.88
2.47
1.98
2.25
3.77
3.63
3.73
4.32
2.97
3.77
3.45
3.60
0.1280
0.2559
0.075
0.06
4.4
<0.001
3.01
0.099
8.4
<0.001
2.73
2.67
2.92
2.96
0.1280
0.2559
0.076
0.118
3.83
3.85
3.88
3.95
0.053
4.4
0.128
0.636
30
57
3.38
3.14
3.28
3.28
2.84
4.07
2.60
3.83
0.078
7.1
<0.001
0.1319
15.6
0.787
0.1541
11.2
<0.001
3.23
0.1453
13.3
<0.001
0.0847
8.5
<0.001
3.14
3.47
3.29
3.32
0.099
4.4
0.018
0.384
3.28
4.02
3.80
4.19
0.096
7.1
<0.001
0.919
2.40
2.31
2.44
2.40
0.1319
15.6
0.787
0.079
3.58
4.04
3.86
4.12
0.1379
11.2
0.001
0.474
2.56
3.35
3.11
3.32
0.1453
13.3
<0.001
0.331
3.16
3.58
3.62
3.49
0.0978
8.5
<0.001
0.187
45
58
45
56
45
58
3.39
3.27
3.11
4.04
3.37
3.41
3.12
Fungicide
Nil
Autumn
Spring
Full
SED
CV%
F prob
Interaction F
prob
DF
3.085
3.41
3.365
3.47
Table 11. Canker indices in cultivar x fungicide experiments, 1999-2002.
Site
Year
1999
Boxworth
2000
2001
2002
High Mowthorpe
2000
2001
1999
2002
Mean
Variety
Pronto
Apex
Alpine
Contact
Escort
Licrown
Lutin
SED
CV%
F prob
Fungicide
Nil
Autumn
Spring
Full
SED
CV%
F prob
Inter F
DF
31.5
25.9
32.9
23.8
15.0
19.9
12.6
24.4
16.2
46.9
31.8
23.2
23.0
13.1
35.1
3.70
31.9
0.043
2.629
39.4
<0.001
15.8
1.746
28.4
<0.001
42.7
33.1
24.7
13.1
3.70
31.9
<0.001
0.827
27
34.6
23.0
14.1
3.7
2.351
39.4
<0.001
<0.001
57
29.9
12.3
20.2
7.2
1.746
28.4
<0.001
0.041
45
(angles)
10.50
3.25
1.33
0.46
7.44
0.79
15.0
17.3
9.2
0.31
1.81
1.81
1.25
20.2
1.62
3.27
29.8
<0.001
4.22
77.4
0.078
0.920
191.0
0.4481
2.87
2.040
48.8
<0.0011*
0.536
215.6
0.2651
61.9
28.6
47.2
14.0
3.77
29.8
<.001
0.375
58
19.2
15.9
15.8
10.8
4.22
77.4
0.268
0.675
45
4.10
0.20
0.90
0.25
0.823
191.0
<0.001
0.615
57
12.75
3.94
4.62
2.75
2.040
48.8
<0.001
0.378
45
1.28
0.50
1.28
0.39
0.619
215.6
0.311
0.405
58
1 = data had a skewed distribution. * = Angular transformed data presented.
16
19.18
13.96
15.95
6.92
14.11
17.00
9.34
25.80
14.69
16.10
6.52
AR0212
Project
title
Improved management strategies for diseases of oilseed rape MAFF
project code
AR0212
Discussion
Sclerotinia stem rot
The project has provided new data on various aspects of petal biology. The sequence of flowers opening and petal fall
have been quantified for a range of sites and cultivars and could be used to predict when petal fall is likely to occur. The
distribution of petals caught within the crop canopy has also been established and links the greatest petal retention at the
mid-plant level where stem rot symptoms are frequently located. Some stem rot lesions occur at the base of the stem and
these are most likely to occur at early to mid-flowering when the lower leaves are still present.
The importance of petal infection in the assessment of risk of sclerotinia has been confirmed through regression analyses
of data collected during 1993-1998. Individual site data from this project identified mainly low levels of petal infection
and low stem rot infection. There was one anomaly in 1999, when crop infection reached 27-32% plants affected, but no petal
infection was recorded on any of the three sampling dates. Further work is required to develop rapid diagnostic tests
for sclerotinia which would allow farmers to identify fields with high levels of sclerotinia ascospores. Weather factors,
as well as inoculum, are also important for sclerotinia infection. Regression models for each year during 1993-1998
identified different combinations of temperature and rainfall variables which were important. It would appear that
conditions favouring infection are lax, occurring at various times during flowering and with different combinations of
rainfall and temperature. During this project, artificial inoculation of leaves with mycelial disks resulted in stem rot
lesions and suggested that primary inoculum and conditions leading to initial leaf infection are the most important
limiting factors.
Phoma leaf spot and canker
There was considerable variation in the timing and severity of phoma leaf spot and canker epidemics between sites and
seasons. Sow date effects were also marked in some years. This has provided contrasting datasets which have been used
to develop improved guidance on disease management in autumn. The project showed than later sown plants had more
severe infection (% leaf area affected) but fewer spots per plants than earlier sown plants. This explains previous disease
survey observations which indicated that September sown crops tend to have more severe phoma leaf spot than August
sowings. Sowing in late August offers a practical opportunity to produce a strong plant on which most phoma epidemics
can be managed. If crops establish late, very prompt action with fungicides will be required as phoma spotting starts to
appear. Early sown plants may not justify a fungicide treatment if phoma leaf spot only develops from late November
onwards.
Boxworth is in a high risk area for phoma canker yet the untreated index was only >50 in one year out of four in this
project. All the untreated canker indices were >20 at High Mowthorpe. Yield loss from phoma canker occurred when
canker indices were >25 and was most marked (0.7 t/ha) in 2002 when the untreated index was 61.9. Identification of
similar high risk situations is essential if fungicides are going to be used cost-effectively. Cultivar resistance had a
significant effect on canker development, but the degree of canker control achieved by increasing disease resistance from
5 to 7 (on a 1-9 scale) was smaller than could be achieved with two fungicide sprays.
Conclusions and relevance to policy
This project addresses the Defra policy objective of reducing pesticide use by identifying opportunities to improve targeting
of treatments, which provides benefits for protection of the public and the environment. In addition, better use of inputs
contributes to the objective of sustainable agriculture. The work provides new insights into epidemiology and management
of the major pathogens in oilseed rape. The principles established allow development of commercial strategies with support
from HGCA and other industry funding. Defra- and HGCA-funded work has been transferred to industry through meetings,
conferences and press publications and this has contributed to changes in fungicide timing in autumn. Improved
understanding of disease management and the data are being exploited through the SAPPIO LINK–funded PASSWORD
project. Further reductions in fungicide use are possible if reliable and quantitative measures of inoculum can be obtained at
the individual crop level. Rapid diagnostic tests are available and would be beneficial for sclerotinia and light leaf spot in
particular. Disease resistance could be more widely exploited but will require understanding of pathogen variation and also
crop traits that confer durable resistance. There is opportunity to explore such traits within the Defra oilseed rape Crop
Genetic Improvement Centre.
17
Project
title
Improved management strategies for diseases of oilseed rape MAFF
project code
AR0212
Main implications of findings
Sclerotinia stem rot infection was not influenced by seed rate as crop growth compensated for low seed rates by
producing more flowering shoots. Only small effects on crop microclimate were detected at the early flowering stage in
relation to varying seed rate and use of cultivars with reduced petals. There appear to be limited opportunities to modify
crop agronomy to significantly reduce the risk of sclerotinia infection. Truly apetalous types offer some prospect of
modifying the within-crop environment, but greater benefits are expected because petals are no longer available to
stimulate plant infection.
The incidence of sclerotinia on petals was selected as an important factor along with weather factors for predicting stem
rot incidence. The field monitoring and experimental sites during 1993-2002 have shown that severe attacks of sclerotinia
(>20% plants affected) are uncommon. The challenge is therefore to identify about 5% of crops where sclerotinia is
likely to cause significant yield loss and, more importantly, to guide decisions not to apply fungicides in low risk
situations. In practice, however, some farmers are unlikely to accept sclerotinia infection in their crops because of the
threat to future cropping.
Rapid detection methods to detect ascospores or petal infection levels are still required to improve decision making.
The rate of flowers opening and petal fall were quantified for the whole flowering period. Flowers persisted longer at
early flowering than at mid- to late flowering when flowers survived for less than three days. The rates of flower opening
and petal loss were very similar when calculated on a thermal time basis. Petal fall occurred mainly from mid-flower
onwards, after 50% of the main raceme had flowered and this could now be predicted to assist risk assessment of
sclerotinia.
The conditions leading to petal sticking are quite variable in relation to the type and duration of rainfall. Light rain is most
conducive to petal sticking, but some sticking will occur after heavy rain. Petals stick ‘events’ (when several petals stuck
to an individual leaf) were not common, occurring on only 2-3 occasions per crop. These ‘events’ were associated with
petal fall, periods of rain , and leaf wetness duration of about 12-24 hrs. These criteria could be combined with detailed
weather forecasts and used to develop a warning scheme for farmers.
The relationships between phoma leaf spot and canker have been quantified in collaboration with Rothamsted Research
(in AR0211) and new guidance on the effects of differently timed epidemics developed. Early phoma leaf spot epidemics
which occur in September or October are the most important for yield loss. In contrast, there is little risk to yield from
phoma leaf spotting which develops from late November onwards on well-grown plants.
Sowing in late August or early September resulted in higher yields than later sowings. This was attributed to better
establishment and more effective disease management despite earlier and more frequent phoma leaf spotting in earlier
sowings. Phoma canker can be managed if plants have reached at least the 6-leaf stage when phoma leaf spot starts to
develop. Improved control of phoma canker can be achieved by the integration of cultivar resistance, plant size and
fungicides. Previous research suggested that the first fungicide spray must be applied at the onset of phoma leaf spotting,
but it has now been shown that there is greater flexibility in spray timing (demonstrated in HGCA-funded experiments) if
plants have reached GS1,6-1,7. Early establishment is now regarded as a valuable component of disease management
strategies which industry can now implement.
References
Davies J M Ll, Gladders P, Young C, Dyer C, Hiron L, Locke T, Lockley D, Ottway C, Smith J, Thorpe G & Watling M,
1999. Petal culturing to forecast sclerotinia stem rot in winter oilseed rape: 1993-1998. Aspects of Applied Biology
56,129-134.
Sylvester-Bradley R & Makepeace RJ, 1984. A code for stages in development in oilseed rape (Brassica napus L.).
Aspects of Applied Biology 6, Agronomy, physiology, plant breeding and crop protection of oilseed rape, pp. 399-419.
18
Project
title
Improved management strategies for diseases of oilseed rape MAFF
project code
AR0212
Action resulting from the research
Data from the project have been used in modelling of phoma development in the PASSWORD Decision Support System,
which is subject to an IP agreement. Contributions are also being made to the SECURE project (EU-funded) on
sustainable disease resistance using Leptosphaeria maculans on oilseed rape as a model system. Industry funding has
supported work on developing commercial fungicide treatments and in the rapid dissemination of disease information via the
Internet.
Technology transfer
Work from this project has been published in refereed scientific papers (7), two book chapters, conference proceedings (7)
and reported in agricultural press articles. It has been presented to scientists as talks and posters at international conferences
(5), including BCPC Brighton conferences, and to farmers, advisers and agrochemical company training events (4) and the
press as talks and poster/field plot demonstrations. National Cereals, Sprays and Sprayers and HGCA events (5) have been
attended and regular crop advisory information published through ADAS Crop Action notes and via telephone contact.
Support for technology transfer has been forthcoming from HGCA and the agrochemical industry. Web-based disease
forecasts have been produced and modelling of epidemiological and fungicide data is now in progress as part of the SAPPIO
LINK PASSWORD project.
Possible future work
Projects will be allied with priorities within the Oilseed Rape Crop Genetic Improvement Centre (OREGIN)
1. To investigate the variation in pathogenicity and changes in pathogen populations in relation
to selection pressure from different cultivars for L. maculans and P. brassicae.
2. To identify virulence factors present in the L. maculans population in England and identify strategies for exploitation
of genetic disease resistance.
3. To determine and evaluate factors which contribute to disease escape and disease tolerance.
4. To establish the benefits of apetalous oilseed rape for management of sclerotinia in oilseed rape.
5. To develop and test novel methods to monitor airborne primary inoculum of S. sclerotiorum, L. maculans and P.
brassicae in the field, based on DNA detection or antibody detection.
6. To evaluate and incorporate inoculum and improved weather parameters into decision guidelines for control of S.
sclerotiorum.
7. To improve and validate forecasting models for primary inoculum for use in different geographic regions and in
relation to changing agronomic practice.
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