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Abstract

In 1998, a survey of the incidence and severity of diseases was carried out on 30 crops of winter linseed at early flowering and again at crop maturity. Five crops each were selected in south west, east, east Midlands, west Midlands and north of England and from Scotland. Crops were predominantly cv. Oliver (90% crops), grown from certified seed (83%) and sown in September (97%). Pasmo (Mycosphaerella) was the most important disease, affecting leaves of 73% crops at early flowering and 90% crops at maturity. Powdery mildew (70% crops), Alternaria (30% crops) on leaves and Botrytis on capsules (70% crops) were also common. Regional differences were apparent for powdery mildew, which was present in all regions except the southwest, whilst Alternaria predominated in the Midlands. Half of the crops surveyed had received fungicide sprays, but this appeared to have made limited impact on disease severity. Pasmo is a new threat to UK linseed crops and this raises concerns about the threat it poses to spring linseed.

In 1999, a survey of the incidence and severity of diseases was carried out on 30 crops of winter linseed at early flowering and again at crop maturity. Five crops each were selected in south west, east, east Midlands, west Midlands and north of England and from Scotland. Crops were predominantly cv. Oliver (93% crops), grown from certified seed (70%) and sown from mid September to mid October. Pasmo (Mycosphaerella) was the most important disease, affecting leaves of 83% crops at early flowering and 80% crops at maturity. Powdery mildew (24% crops), Alternaria (13% crops) on leaves and Botrytis on capsules (83% crops) were also common. Regional differences were apparent for powdery mildew, which was present mainly in the west Midlands and Scotland and much less common in the east than in 1998. Alternaria predominated in the south west. There was an increase of 30% in the use of fungicide sprays and 73% of crops surveyed had been treated. Tebuconazole plus MBC during flowering was the most widely used fungicide treatment. This appeared to have made some impact on disease severity. Pasmowas less severe in 1999 than in 1998 and this contributed to higher yields. This disease became established more slowly in the autumn and winter than in 1997/98 and understanding this phase of the epidemic could lead to improved control strategies.

In 2000, a survey of the incidence and severity of diseases was carried out on 30 crops of linseed at early flowering and again at crop maturity. Because of the rapid decline in winter linseed cropping, samples were taken in equal numbers from winter and spring linseed crops in England. Sampling reflected the areas of production and comprised six crops (five spring linseed) in the south west, nine crops (five spring linseed) in east, five crops (two spring) in east Midlands, five crops (one spring) in the west Midlands and five crops (two spring) in the north of England. Winter linseed crops were all cv. Oliver and spring linseed was represented by eight cultivars. Certified seed was used for 70% of crops and sown during mid September to mid October for winter crops and early March to early May for spring crops. Pasmo (Mycosphaerella) was the most important disease, affecting leaves of 70% crops at early flowering and 80% crops at maturity. Powdery mildew (43% crops), Alternaria (13% crops) on leaves and Botrytis on capsules (90% crops) were also common. Regional differences were apparent for powdery mildew, which was most prevalent in the east at early flowering and in the south by crop maturity. Alternaria was confined to the south. Fungicide sprays were used on 47% crops, of which 40% was on winter linseed. Treatments were applied mainly during the early to mid flowering period and appeared to have made a limited impact on final disease severity. It is clear that pasmo is a threat to spring linseed crops and further monitoring is advisable to see if the disease declines in the absence of winter linseed cropping.

In winter linseed experiments at Rothamsted in 1997/98, 1998/99, and 1999/2000 different fungicides were applied in autumn and at pre-flowering, mid-flowering or capsule development stages to control diseases. In 1997/98, pasmo developed early in the season and became very severe in June/July after high March/April and June rainfall. Pasmo was well controlled by a single application of benomyl at mid-flowering and yield was more than doubled; a two-spray programme provided little additional control. However, in 1998/99 and 1999/2000 pasmo developed later, there was less rainfall in March/April and June and pasmo did not become as severe as in 1997/98. Fungicide applications did not decrease disease severity and there was little yield response in these two seasons. Regression analyses suggest that yield responses could be related to the control of pasmo on leaves in June and on stems in July. Therefore a simple model using the stem pasmo severity at crop maturity (x) as the explanatory variable was selected to estimate yield loss (yr) retrospectively for each season. These models were applied to five regions in England to estimate regional and national losses.

The estimated natural costs of yield losses caused by this disease were £28M in 1998, £1M in 1999 and £0.5M in 2000 in the UK. Correctly timed fungicides can provide good control in years when pasmo is serious, but in some years there was no evidence that fungicides improve yields of winter linseed. Since the incidence and severity of pasmo varies between regions and seasons, a decision-making aid would help predict in what crops there might be an expected effect of pasmo. A model can be used in spring to estimate the development of the disease to predict the possible yield loss due to pasmo and hence aid fungicide decision-making.

Results suggest that application of fungicides to winter linseed to increase yield by disease control may be justified in one year out of three when pasmo epidemics are severe (in two years of this three year study pasmo did not become sufficiently severe). When pasmo disease was first observed on leaves later than January, it did not become sufficiently severe to reduce yields, even on untreated plots. Data from untreated plots indicate that in 1997/98, when the pasmo epidemic on leaves started earlier, stem disease was first observed in March. By contrast, it was not observed until May in 1998/99 and 1999/2000 when it did not become sufficiently severe to cause yield loss. Therefore, the results suggest that growers should only apply pre/mid-flowering sprays if stem disease is present in March.

Summary

Winter-sown linseed was introduced commercially to the UK in 1995 as an alternative to spring-sown linseed. Spring linseed can pose problems for harvesting because of its late maturity so that it is difficult to include in arable rotations. When this project was started in 1997, there had been little research into diseases of winter linseed but surveys had shown widespread, severe epidemics of pasmo (caused byMycosphaerella linicola) in many commercial crops, causing considerable yield losses. In 1997, there were indications that diseases would be an important constraint to the success of the winter linseed crop in the UK, with widespread severe attacks of pasmo causing serious yield losses on winter linseed (at all ADAS centres and on many commercial crops) suggesting that the most damaging diseases on winter linseed may be different from those on spring crops (on which Botrytis and Alternaria had been the predominant diseases). However, in 1997 good control of diseases and lodging was achieved in ADAS winter linseed trials, with yield responses in the region of 25%. As the area of linseed grown was expected to expand, the incidence and severity of diseases on the crop were also likely to increase and this series of field experiments were done to investigate the effects of disease on crop growth and yield.

This project included a three-year survey of diseases of winter linseed co-ordinated by Dr. Peter Gladders (ADAS, Boxworth), data analyses and a three-year programme of field experiments at Rothamsted co-ordinated by Sarah Perryman. The overall aims of this project were:

To determine the occurrence of diseases on winter linseed crops in the UK (ADAS);
To quantify effects of diseases on growth and yield of linseed crops, using fungicides;
To identify factors affecting the incidence and severity of diseases on linseed;
To evaluate the importance of diseases in winter linseed crops in the UK.
1. Disease survey 1998-2000

The objective was to determine the incidence and severity of diseases on winter linseed and identify factors that affect the occurrence of disease problems.

Methods

In 1998, a total of 30 crops of winter linseed were selected for the survey with five crops being selected in each of the following six regions: South west England, Northern England, Eastern England, East Midlands, West Midlands, Scotland. Crops were selected by ADAS in England using growers known to ADAS and/or Semundo. Sites for sampling in Scotland were identified by Semundo. In 1999, there were few crops in Scotland and three samples were taken from the Borders region to augment two crops in Scotland. Winter linseed cropping declined sharply in autumn 1999 and the survey in 2000 comprised 15 crops of winter linseed and 15 crops of spring linseed, all collected from farms in England.

Samples of 50 plants were collected at early flowering (late May/early June) and at crop maturity (as capsules turned yellow) in early July by ADAS and by local agronomists or farmers in Scotland and the Borders. A sub-sample of 25 plants was examined in detail, with records of the incidence and severity of individual diseases and other symptoms being recorded on the leaves, stems and capsules on each plant. Disease assessments were carried out locally by ADAS Plant Pathologists and samples from Scotland were assessed at ADAS Boxworth. Agronomic and cropping details were collected for each site and data was collated and stored at ADAS Boxworth.

Key results

1998

Pasmo was the most common disease in winter linseed crops in 1998 and it was found on leaves of 73% crops at early flowering and 90% crops at maturity.
Pasmo was the most common stem disease affecting 63% crops at early flowering and 87% crops at maturity.
Powdery mildew was found in all areas (70% crops affected at early flowering) and was more common than pasmo at early flowering in the north of England and Scotland, but was less common at crop maturity (50% crops affected).
Alternaria leaf spot increased from 13% crops affected at early flowering to 30% crops affected at crop maturity.
Botrytis caused some leaf spotting in 7% crops at both early flowering and crop maturity, stem rotting in 10% crops and capsule rots in 70% crops.
Minor stem diseases included Phoma spp. (1 crop), Sclerotinia (1 crop) and Fusarium spp. (2 crops).
Crop lodging was severe in many crops and averaged over 60% crop area in the east and east Midland areas.
Weed cover averaged less than 5% area affected, except in the south west and north of England, which averaged 30% and 11% area affected, respectively, at crop maturity.
Invertebrate pest damage was limited and frequently below 1% leaf area affected. Pigeons gave cause for concern with late and severe grazing in the spring.
The main cultivar was Oliver, grown predominantly from certified seed.
Fungicide sprays were used on 50 % of crops and appeared to have a limited impact on disease severity. Tebuconazole and MBC products were the most frequently used fungicides.
The combination of severe lodging and high disease contributed to low yields in 1998. Fungicide sprays have the potential to overcome disease and increase yields by at least 1 t/ha.
Reports of pasmo on spring linseed are of concern and the disease appears to have become prominent since (probably as a direct result of) the introduction of winter linseed.
1999

Pasmo was the most common disease in winter linseed crops in 1999 and it was found on leaves of 83% crops at early flowering and 80% crops at maturity.
Pasmo was the most common stem disease, affecting 55% crops at early flowering and 90% crops at maturity.
Powdery mildew was less common than in 1998 and was found mainly in the west Midlands and Scotland (24% crops affected at early flowering) and was slightly less common at crop maturity (20% crops affected).
Alternaria leaf spot increased from 7% crops affected at early flowering to 13% crops affected at crop maturity.
Botrytis caused some leaf spotting in 3% crops at early flowering and 13% crops at crop maturity, stem rotting in 23% crops and capsule rots in 83% crops.
The minor stem diseases, including Phoma spp., Sclerotinia and Fusarium spp.were not recorded in 1999.
Crop lodging was severe in a few crops and averaged 35% crop area in the eastern counties and <10% in other areas.
Weed cover averaged less than 5% area affected in the north of England and west Midlands, but averaged 31% at crop maturity in the south west.
Invertebrate pest damage was limited and below 1% leaf area affected in all except two crops at early flowering. Pigeons gave cause for concern with late and severe grazing in the spring.
The main cultivar was Oliver, grown from predominantly from certified seed.
Fungicide sprays were used on 73 % of crops and appeared to have some impact on disease severity. Tebuconazole and MBC products were the most frequently used fungicides, mainly applied as single sprays during flowering.
The combination of limited lodging and much less severe pasmo disease contributed to improved yields in 1999 compared with 1998.
Crop monitoring in winter may be a useful early indicator of disease risk.
2000

The monitoring in 2000 was confined to England and included equal numbers of spring and winter linseed crops.

Pasmo was the most common disease in linseed crops in 2000 and it was found on leaves of 70% crops at early flowering and 90% crops at maturity.
Pasmo was the most common stem disease, affecting 57% crops at early flowering and 73% crops at maturity. Pasmo showed a higher incidence in winter linseed than spring linseed on leaves at early flowering (85% and 16% plants affected respectively) and crop maturity (63% and 30% plants affected respectively). Similar differences were apparent on stems.
Powdery mildew was found in all areas except the west Midlands and appeared after early flowering in the north (overall 20% crops affected at early flowering, 43% crops affected at crop maturity). It was more severe than pasmo at crop maturity, affecting up to 41% leaf area in the south. Powdery mildew was only found at early flowering in spring linseed and this difference was largely maintained at crop maturity when 4% of winter linseed plants and 51% spring linseed showed foliar symptoms.
Alternaria affected leaves and capsules at crop maturity in 13% crops in the south.
Botrytis caused some leaf spotting in 10% crops at early flowering and 33% crops at crop maturity. Botrytis stem rot occurred in 7% crops (both crops were spring linseed) and Botrytis capsule rots in 90% crops. No other stem diseases were recorded.
Fine black spotting was very prevalent in winter linseed at early flowering (59% plants affected) and persisted on winter and spring crops up to crop maturity.
Crop lodging was only significant in two crops in the east Midlands at early flowering and affected >10% of crop area at five sites by crop maturity. Lodging was predominantly in winter linseed and associated with the tallest crops.
Weed cover averaged less than 5% area affected, except in the south and north of England, which averaged 17% and 18% area affected respectively crop maturity.
Invertebrate pest damage was limited and frequently below 1% leaf area affected, reaching 5% damage in occasional spring linseed crops in the east.
For winter linseed only the cultivar Oliver was grown, whereas eight different spring linseed cultivars were used spring cropping. Crops were grown predominantly (70%) from certified seed.
Fungicide sprays were used on 47% of crops and appeared to have some impact on disease severity.Tebuconazole and MBC products were the most frequently used fungicides, with early to mid flowering timing. There was a large difference in fungicide use between winter and spring linseed, with 80% and 13% crops respectively receiving foliar sprays.
Confirmation of severe pasmo in spring linseed is of concern and fungicide decision-making on spring crops will need to take account of the increased risk of yield loss from this disease.
2. Effects of diseases on growth and yield of linseed crops

These experiments provide opportunities to compare and contrast the effects of diseases on yields of winter and spring linseed crops at Rothamsted in three seasons (1997/98, 1998/99, and 1999/2000). Data analyses to establish relationships between disease incidence/severity and crop growth/yield loss were investigated with existing data from spring linseed (1988-1998) and with the new winter linseed field experiment data.

Methods

Field experiments were done at Rothamsted in three seasons (1997/98, 1998/99 and 1999/2000) using the cultivar Oliver. Plots received experimental treatments of different fungicides at different timings to manipulate the severity of diseases: - tebuconazole (Folicur), benomyl (Benlate), iprodione (Rovral Flo) and thiophanate-methyl plus iprodione (Compass). They were applied in autumn (tebuconazole ) or at pre-flowering, mid-flowering or capsule development stages. Regular assessments were made of the disease symptoms on leaves, stems and capsules and of effects of diseases on crop growth, thousand seed weight and yield. Detailed weather information (temperature, rainfall, leaf wetness/duration) was collected using an automatic weather station and numbers of pathogen spores being dispersed were monitored with a Burkard spore sampler. Data analyses to establish relationships between disease incidence/severity and crop growth/yield loss were applied to existing data from spring linseed (1988-1998) and to the new winter linseed field experiment data.

Key results

Winter linseed:

The only disease to occur at more than trace levels was pasmo.
In 1997/98, pasmo symptoms were evident earlier in the season than in 1998/99 and 1999/2000.
Pasmo was well controlled in the first season and consequently yield was more than doubled.
The best treatment in this first season was a single application of benomyl at mid-flowering; a two-spray programme provided little additional control or yield response.
An autumn application of tebuconazole did not have a long-term effect on disease or yield.
There was insignificant disease control and little yield response in the later two seasons; however, untreated yields in these two seasons were significantly higher than those in the first season.
When pasmo occurred late in the season, resulting in lower % area of stems affected, flowering treatments did not decrease disease levels and increase yields.
Regression analyses suggested yield responses could be related to the control of pasmo on leaves in June and on stems in July.
Thousand seed weight was related to yield, indicating yield gain at flowering/ post-flowering due to seed formation.
These results therefore suggest that application of fungicides to winter linseed to increase yield by disease control may be justified in only one year out of three when pasmo epidemics become sufficiently severe.
Decisions about whether to apply fungicides or not may be made in March; if there is a 20% area of stem affected by pasmo disease it is recommended to apply a pre or mid-flower spray of benomyl.
Spring linseed:

Analyses of data from spring linseed field experiments for 1988-1998 suggests that substantial yield losses occurred in three years and only slight losses in other years.
These yield losses were related to decreases in yield components (TSW and numbers of capsules).
Percentage leaf area with browning was the disease factor most consistently related to yield losses (in five years) and for each 10% increase in leaf area with browning there was a yield loss of 0.10-0.18 t/ha.
Yield losses were greatest in years when the period of flowering and early capsules development in June and July was wetter than average.
The predominant disease was grey mould (Botyrtis cinerea) in wet years up to 1996, whereas pasmo (Mycosphaerella linicola ) was most important in 1997 and 1998.
Observed yield losses were small in hot dry years when powdery mildew (Sphaerotheca lini) and verticillium (Verticillium dahliae ) were the predominant diseases.
3. Factors affecting severity of diseases on linseed

Weather, sowing date, previous cropping and air-borne spore numbers may affect the severity of diseases on linseed crops. Effects of weather were examined for existing spring linseed data since 1988 and for winter linseed experiments from 1997/98 -1999/2000.

Methods

Detailed weather information (temperature, rainfall, leaf wetness/duration) was collected using an automatic weather station and numbers of pathogen spores being dispersed were monitored with a Burkard spore sampler. These were recorded and examined using regression to identify which factors have the greatest influence on severity of different diseases. Incidence of fungal pathogens on linseed was investigated using culture on agar of seeds from infected plants.

Key results

Winter linseed:

In 1997/98 when the linseed was sown in September, pasmo disease developed earlier and was subsequently severe, with a resulting loss in yield, than when the seed was sown in October in 1998/99 and 1999/2000.
There was no definite relationship between the weather pattern in 1997/98 and the early outbreak of pasmo. However, in 1997/98 pasmo became very severe in the spring when there was high rainfall in March/April.
In 1998/99, there was less rainfall in March/April than in 1997/98 and pasmo did not become so severe.
M. linicola was not detected in seed harvested from field experiments in 1997/98 and 1998/99. There was a very low incidence of M. linicola on the seed in 1999/2000.
B. cinerea was well controlled by benomyl and iprodione treatments in1997/98.
Spring linseed

Yield losses were greatest in years when the period of flowering and early capsule development in June and July was wetter than average.
The predominant disease was grey mould (Botryrtis cinerea) in wet years up to 1996, whereas pasmo (Mycosphaerella linicola ) was most important in 1997 and 1998.
Observed yield losses were small in hot dry years when powdery mildew (Sphaerotheca lini) and verticillium (Verticillium dahliae ) were the predominant diseases.
4. Importance of diseases in winter linseed in UK

Methods

Results from the ADAS linseed disease survey were combined with the yield loss relationships derived from field experiments to estimate, retrospectively, the losses from pasmo disease severity nationally to determine the economic importance of the disease.

Key results

Estimated national losses were c. £2M in 1998, £1M in 1999 and £0.5M in 2000.
These losses represented 44% in 1998, 31% in 1999 and 47% in 2000 of the total possible net gain in linseed yields.
5. Conclusions and implications for growers

Introduction of winter linseed has brought a significant new disease threat to linseed cropping. Pasmo is capable of causing >50% yield loss and contributed to poor performance of winter linseed crops in 1998-2000.
Pasmo became established in all regions where linseed was monitored even when linseed was grown for the first time. It could be seed-borne but air-borne ascospores from crop residues in autumn are now implicated in early disease establishment.
Spring linseed is also affected by pasmo and fungicide strategies need to be adjusted for spring crops.
Fungicides can be very cost-effective when pasmo and other diseases are controlled. Aim to protect the upper leaves and capsules. A broad-spectrum treatment such as tebuconazole + carbendazim has proved cost-effective at early to mid flowering.
Epidemiology of pasmo is poorly understood - rain is required for spore dispersal and infection and the latent period could be 3-4 weeks in spring.
Powdery mildew is common in winter and spring linseed but economic damage is thought to be small.
Botrytis is common on capsules and also as stem and leaf rot in a few crops, causing limited losses in most crops. Alternaria leaf spot was found in the wetter areas of the south west and west Midlands but is likely to be masked by severe pasmo.
Sclerotinia and Phoma spp. stem rots were only found in single crops in1998; Fusarium spp.occurred in two crops.
Lodging was a common problem in 1998 and occasionally severe in 1999 and 2000. The most severe lodging was associated with tall crops (>80 cm tall).
Weed problems were most severe in the south west and north where >10% ground cover was recorded.

HGCA Project Number: 1539 
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