the encyclopaedia of oilseed rape diseases - BASF Crop Protection ...

THE 

ENCYCLOPAEDIA OF 

OILSEED RAPE 

DISEASES

How to use this Encyclopaedia 

The main diseases of oilseed rape in the UK are included in this 

encyclopaedia. They are listed in alphabetical order of their common 

names. The Contents page provides a reference list of diseases that can 

be used to locate them in the text. There are descriptions of the 

symptoms supported by colour photographs and disease life-cycle 

diagrams. For each disease, the host range of the pathogen and its life 

cycle are described with details of its importance and broad guidance 

on how to control it. 

Summary tables covering sources of diseases (table 1), components of 

disease control (table 2) and the periods for the control of key diseases 

with foliar sprays (table 3) are at the end of the disease section, pages 

51-53 and the importance of various control measures are also 

included. 

For further information on BASF oilseed rape fungicides contact the 

Technical Services Hotline on 0845 602 2553. 

Cover image background: Aerial view. 

Inset pictures from top down: Rhizoctonia Foot Rot, Ring Spot, Phoma Leaf Spot, 

Transverse section showing Stem Canker Disease, Grey Mould.

Introduction 

INTRODUCTION 1 

Oilseed rape production has expanded since its re-introduction in the early 

1970’s to over 600,000 ha in the UK. Over 95% of the crop is winter 

oilseed rape. It has been a profitable break crop competing with second 

wheats and this has led to shortening of rotation to 1 in 2 or 1 in 3 years 

within the last decade. The consequences of this, together with changing 

climatic conditions, have increased disease problems. 

The value of rapeseed increased to over £300/tonne in 2008 and decision 

making needs to be fine-tuned as inputs to recover even small yield 

improvements may be cost–effective – a marked change from the situation 

when rapeseed was £120-150/tonne. Identification and understanding of 

diseases is a key part of improved decision making. New problems such as 

verticillium wilt are emerging as well as changes in pathogen populations, 

and different patterns of disease development from year to year. We hope 

that this booklet will improve awareness of these threats. 

Authors 

ADAS 

Peter Gladders Denise Ginsburg Faye Ritchie Julie A.Smith 

BASF 

Steve Waterhouse Clare Tucker Lindy Tonguç

2 

CONTENTS 

Contents 

Introduction ............................................................................... 1 

How to use this Encyclopaedia....................... Inside Front Cover 

Diseases (Common Name) General Photo 

Section Library 

Blackleg.................................................................................... 22 86 

Clubroot..................................................................................... 4 71 

Damping off, Rhizoctonia root rot ............................................ 8 72 

Dark leaf and pod spot ........................................................... 10 73 

Downy mildew......................................................................... 13 76 

Grey mould .............................................................................. 15 78 

Light leaf spot .......................................................................... 18 81 

Phoma leaf spot and stem canker, Blackleg ............................. 22 86 

Phytophthora root rot ............................................................. 26 98 

Pod spot ................................................................................... 10 73 

Powdery mildew....................................................................... 28 99 

Rhizoctonia root rot .................................................................. 8 72 

Ring Spot ................................................................................. 30 101 

Sclerotinia stem rot .................................................................. 32 104 

Sooty moulds ........................................................................... 36 111 

Stem Canker............................................................................. 22 86 

Verticillium Wilt....................................................................... 38 112 

Virus diseases - Cauliflower mosaic ......................................... 41 117 

Turnip mosaic ................................................. 43 120 

Turnip yellows ................................................ 45 121 

White blister............................................................................. 47 122 

White leaf spot ........................................................................ 49 124 

White mould ............................................................................ 32 104 

White rust ................................................................................ 47 122 

Pathogen 

Albugo candida ........................................................................ 47 122 

Alternaria brassicae.................................................................. 10 73 

Alternaria brassicicola.............................................................. 10 73 

Alternaria spp. ......................................................................... 36 111 

Botryotinia fuckeliana.............................................................. 15 78 

Botrytis cinerea ........................................................................ 15 78 

Cauliflower mosaic virus (CaMV)............................................ 41 117

CONTENTS Continued 

General Photo 

Section Library 

Cladosporium spp. ................................................................... 36 111 

Cylindrosporium concentricum................................................ 18 81 

Erysiphe cruciferarum .............................................................. 28 99 

Hyaloperonospora parasitica ................................................... 13 76 

Leptosphaeria biglobosa .......................................................... 22 86 

Leptosphaeria maculans........................................................... 22 86 

Mycosphaerella brassicicola ..................................................... 30 101 

Mycosphaerella capsellae ......................................................... 49 124 

Peronospora parasitica............................................................. 13 76 

Phoma lingam .......................................................................... 22 86 

Phytophthora megasperma....................................................... 26 98 

Plasmodiophora brassicae.......................................................... 4 71 

Pseudocercosporella capsellae .................................................. 49 124 

Pyrenopeziza brassicae ............................................................. 18 81 

Pythium spp. .............................................................................. 8 72 

Rhizoctonia solani...................................................................... 8 72 

Sclerotinia sclerotiorum............................................................ 32 104 

Thanatephorus cucumeris .......................................................... 8 72 

Turnip mosaic virus (TuMV).................................................... 43 120 

Turnip yellows virus (TuYV).................................................... 45 121 

Verticillium longisporum.......................................................... 38 112 

Summaries 

Sources of diseases (Table 1) .................................................... 51 

Disease control components – variety, rotation, fungicides, 

seed treatment etc (Table 2) ..................................................... 52 

Fungicides and their use – overview of key timings (Table 3) .. 53 

Glossary................................................................................ 54 

Growth stages............................................................... 58-70 

Photolibrary................................................................. 71-126 

Reference Material and Further Reading.............. 127 

3

4 

CLUBROOT 

Common name: Clubroot 

Pathogen: Plasmodiophora brassicae 

Hosts 

Club root disease can affect all 

cultivated members of the 

Brassicaceae (Crucifer family). 

Crops which often suffer economic 

loss as a result of clubroot include 

oilseed rape, cabbage, cauliflower, 

swede, calabrese and mustard. 

Wild crucifers such as Shepherd’spurse, 

charlock and wild radish are 

also affected. The pathogen has 

many races that are differentiated 

with sets of brassica cultivars. The 

pathogen is able to infect the root 

hairs of various non-crucifers. 

Symptoms 

The first symptoms of club root 

appear in autumn on winter oilseed 

rape. Inspection of the main 

taproot and lateral roots will reveal 

the development of gall formations, 

which are normally solid, white 

and irregular in shape. Later in the 

season, the galls become 

discoloured and rot. On lightly 

infected plants, only small galls 

may be present on the lateral roots. 

Initially, plants may not show any 

foliar symptoms, though wilting 

may occur under dry conditions 

and when the galling is very severe.

Subsequently plants become 

stunted and there is loss of plants 

overwinter in the most severely 

affected areas as the root system 

rots away. Clubroot symptoms are 

commonly localised in patches 

across fields and these may be 

associated with areas where the soil 

is wet or more acid. Occasionally, a 

whole field may be affected. 

Life cycle 

Clubroot is a soil-borne disease and 

the pathogen is more closely related 

to protozoans rather than a true 

fungus. The pathogen survives in 

the soil by means of thick-walled 

resting spores. Exudates from the 

roots of nearby host plants 

stimulate the resting spores to 

germinate and produce motile 

zoospores. If a suitable host is not 

CLUBROOT 

5 

present the resting spores can 

remain dormant for long periods, 

probably more than 20 years. 

Zoospores move through the soil 

water and infect the host plant via 

direct injection mechanism into the 

root hair, subsequently developing 

into a plasmodium. This structure 

eventually divides to form 

secondary zoospores which invade 

the root cortex and form 

plasmodia, or pass through the wall 

of the root hair and back into the 

soil where they are able to infect 

new plants. As these secondary 

plasmodia develop they stimulate 

enlargement and increased cell 

division of host cortical cells, 

leading to the characteristic galls 

seen on roots of infected plants. 

Upon maturity the secondary 

plasmodia form new resting spores.

6 

CLUBROOT 

Secondary soil organisms cause 

decay of the root galls and resting 

spores are released back into the 

soil. The infection cycle is sensitive 

to temperature as little spore 

germination takes place below 

16ºC, and host infection is 

favoured by temperatures of 18- 

26ºC. The soil must also be moist 

to enable zoospores to cause 

infection. In winter oilseed rape, a 

second phase of clubroot may 

occur in spring and summer as 

temperatures rise. Spring oilseed 

rape is also susceptible and may be 

severely affected if crops are under 

drought stress later in the season. 

Clubroot can be spread around 

the farm on farm equipment, in 

manures and by floodwater. 

Importance 

Clubroot incidence has increased in 

recent years, particularly where 

oilseed rape and other susceptible 

Pictures: Clubroot disease in oilseed rape. 

crops have been grown on short 

rotations, and soils are acid and 

wet or poorly drained. Although 

yield loss is not usually significant 

at a national level, losses of 5-10% 

are common and a few individual 

crops may be completely destroyed. 

Control 

Rotations with brassicas grown one 

year in five and soil pH maintained 

at 7.0-7.3 provide basic control of 

clubroot. Where the disease has 

occurred, liming is advised to 

achieve control by raising both the 

pH and the free calcium status of 

the soil. Drainage problems should 

also be remedied. The winter 

oilseed rape variety Mendel has 

useful resistance to clubroot, but 

may still develop small galls. Soil 

tests for clubroot are available from 

SAC, Edinburgh and these can be 

used to determine the risks of 

clubroot in fields prior to cropping.

Clubroot 

Plasmodiophora brassicae 

CLUBROOT 

7

8 

DAMPING OFF, RHIZOCTONIA ROOT ROT 

Common name: Damping Off, Rhizoctonia Root Rot 

Pathogen: Pythium spp. and Rhizoctonia solani 

(perfect stage Thanatephorus cucumeris) 

Hosts 

Damping off pathogens such 

as Pythium ultimum and 

P. debaryanum have wide host 

ranges. The anastomosis groups 

(AG) of Rhizoctonia solani may 

show some specialisation and differ 

in their temperature requirements. 

Symptoms 

Damping off includes seed rotting, 

failure to emerge, root rotting and 

collapse of young seedlings soon 

after emergence. Pale brown watersoaked 

lesions develop on the roots 

and may extend into the hypocotyl, 

cotyledons and leaves. Postemergence, 

R. solani causes 

wirestem where the hypocotyl is 

partially rotted leaving a 

constriction so that weakened 

plants may snap off and die. Late in 

the season, Rhizoctonia also causes 

grey lesions near the stem base and 

brown lesions on the taproot. A 

white collar of fungal mycelium is 

sometimes seen just above the soil 

surface on mature stems of oilseed 

rape. This is usually the 

Thanatephorus (sexual) stage of 

Rhizoctonia, but may not be 

associated with root damage. 

Life cycle 

Soil-borne oospores of Pythium 

species germinate in response to 

exudates from seeds and seedlings 

and cause direct infection of

seedlings. They then produce 

sporangia and secondary zoospores 

within a few days and these cause 

further infection. Pythium ultimum 

also survives by means of hyphal 

swellings that also respond to 

nutrient stimuli. Cold and wet 

conditions usually give the worst 

problems as seedling growth is slow. 

Rhizoctonia solani survives in soil 

by means of pigmented hyphae and 

sclerotia. The hyphae form 

infection cushions on the surface of 

the seedling roots and hypocotyl 

and then penetrate these tissues. 

Cool weather favours infection by 

AG2-1 type isolates, whilst AG 4 

isolates are most damaging at high 

temperatures. The brown root rot 

symptoms develop in summer when 

there is high soil moisture and 

cause most damage (e.g. premature 

Main picture: Rhizoctonia seedling damage 

Damping Off, Rhizoctonia Root Rot 

Pythium spp. and Rhizoctonia solani 

(perfect stage Thanatephorus cucumeris) 


9 

ripening) when subsequent weather 

is hot and dry. A root rotting 

Rhizoctonia (AG8) may cause 

patches of stunted growth on 

lighter soils. This species causes 

similar problems in cereals, sugar 

beet and other crops. 

Importance 

Damping off diseases contribute to 

poor establishment. The extent of 

damage is variable though usually 

small in most crops. The damage 

caused by Rhizoctonia root rot has 

not been quantified. 

Control 

Seed treatments with thiram are 

used to control damping-off 

diseases. Management relies to a 

degree on the use of generous seed 

rates for oilseed rape crops.

10 

DARK LEAF AND POD SPOT 

Common name: Dark Leaf and Pod Spot 

Pathogen: Alternaria brassicae and Alternaria brassicicola 

Hosts 

Alternaria brassicae and A. 

brassicicola have a wide host range 

affecting brassicas and other 

crucifers including weed species. 

Stubble turnips and some 

horticultural brassicas are very 

susceptible to these pathogens. 

Both these Alternaria species often 

occur together, though A. brassicae 

is often the more prevalent. 

Symptoms 

Small black spots (1-2mm 

diameter) are the first symptoms. 

These gradually increase in size 

and become brown “target” spots 

with concentric light and dark 

brown rings. Secondary spotting 

often occurs around the target 

spot and is useful for showing the 

range of lesion sizes. Very fine 

black speckling in isolation is

difficult to identify with certainty 

and may be due to downy mildew 

or physiological effects. Leaf 

spotting can be very extensive and 

lead to early leaf loss. Dark leaf 

spot is difficult to distinguish from 

phoma leaf spots caused by 

Leptosphaeria biglobosa and unless 

there are a range of dark leaf 

spot symptoms microscopic 

examination may be required to 

support a diagnosis. 

During flowering, leaf symptoms 

may develop in the upper leaves 

and bracts and it is often easier to 

identify them by examining the 

underside of the leaf where there is 

less floral debris obscuring the leaf 

surface. At flowering, the target 

spots are easily confused with the 

large grey zonate lesions caused by 

Botrytis, which occur where petals 

have stuck to the leaf. 

Black spots develop on the stem 

and pods. As pod symptoms 

develop they become brown in 

colour and lead to premature 

ripening and pod splitting when 

severe. Dark pod spot is more 

prevalent where the crop is lodged 

and remains damp for long periods. 

However, even in a standing crop, 

pod symptoms become severe and 

often occur in distinct patches or 

foci. Alternaria activity increases 

as plants senesce and continues to 

increase after swathing. 


11 

Life cycle 

Alternaria spp. are commonly seedborne 

and one of the main 

priorities for seed treatment. There 

are numerous sources of infection 

as a new crop emerges including 

crop residues, neighbouring 

brassica crops, volunteers and weed 

hosts. Air-borne spores introduce 

the pathogen into new crops then 

secondary spread occurs within the 

crop. Early sown crops tend to be 

more heavily infected than later 

sown crops. There is usually slow 

spread during the autumn and 

winter followed by spread to upper 

leaves, stems and pods from 

flowering onwards. Alternaria 

problems occur mainly in untreated 

crops and when there are periods of 

wet weather from flowering

12 


onwards. Only 6-8 hours of surface 

wetness are required for infection 

to take place and symptoms appear 

in 4-5 days at temperatures above 

20ºC. Thunderstorms provide good 

conditions for epidemic development. 

During harvesting operations, large 

numbers of air-borne spores of 

Alternaria spp. are dispersed and can 

cause problems in vegetable brassica 

and spring oilseed rape. 

Importance 

Some damage occurs each year, 

mainly in the south of England and 

in lodged crops. Losses can be as 

high as 50% but these are now 

preventable if crops are inspected 

regularly and potential problems 

Dark Leaf and Pod Spot 

Alternaria brassicae and Alternaria brassicicola 

are detected in time for effective 

fungicide treatment. 

Control 

The widespread use of azole 

fungicides for phoma or light leaf 

spot control in autumn/winter 

appears to have reduced the level of 

dark leaf spot in spring compared 

with the 1980s. Many Sclerotinia 

fungicides have good activity against 

dark pod spot and have specific 

label recommendations for its 

control. In seed crops, two fungicide 

applications are often used to 

maintain protection up to harvest. 

Consequently, spraying with a 

specific fungicide eg iprodione, is 

now not usually necessary. 

Pictures: Alternaria on upper leaf surface and Alternaria on pods.

DOWNY MILDEW 

Common name: Downy Mildew 

Pathogen: Hyaloperonospora parasitica (previously Peronospora parasitica) 

Hosts 

Strains of downy mildew are 

specialised on particular host species, 

but some cross infections can occur 

between Brassica species and other 

crucifers. 

Symptoms 

Downy mildew may be present 

throughout the life of the crops on 

winter and spring oilseed rape. 

The first symptoms are white 

sporulating fungal growth on the 

underside of the cotyledons and 

leaves. This soon causes yellowing 

of the infected area, usually in large 

blotches. Under very favourable 

humid conditions, sporulation may 

also be found on the upper leaf 

surface. The yellowed areas show 

irregular dark speckling and become 

13 

bleached in older lesions. The black 

speckling on bleached lesions has 

been confused with Phoma leaf spot 

though the latter is usually greenish 

rather than pale brown on the 

underside of the lesions. Downy 

mildew is most severe on the 

cotyledons and the first one or two 

true leaves. Later in the autumn and 

winter, symptoms are usually less 

severe and may be predominantly 

small black spots or speckling. 

During stem extension and 

flowering, downy mildew can 

increase rapidly and cause extensive 

yellow blotches on the leaves. Pod 

symptoms are also common after 

flowering and range from large 

yellow blotches with sporulating 

fungal growth to small black 

speckling with little sporulation.

14 

DOWNY MILDEW 

Life cycle 

Whilst downy mildew can produce 

oospores (resting spores) that may 

initiatate infection of seedlings from 

soil, the main source of inoculum is 

likely to be from infected volunteers 

and other crops. It may be seedborne, 

though the significance of this 

is not known. Air-borne spores are 

produced in large numbers on lesions 

and some may be spread by rain 

splash. Only a few hours of leaf 

surface wetness are required for 

infection to occur. Disease 

development is very rapid under cool 

moist conditions and the disease 

cycles in less than 5 days under 

optimal conditions. 

Importance 

Downy mildew is important at the 

seedling stage particularly where 

plants are late emerging and growing 

slowly. Heavily infected cotyledons 

are killed and affected seedlings are 

vulnerable to frost kill. The impact 

on yield is difficult to predict. 

Control 

Early sown crops grow quickly 

through the susceptible stages so 

concerns relate mainly to late 

emerging crops. Recent work with 

seed treatments has shown there may 

be improved vigour where early 

control of downy mildew is achieved. 

There is little experimental evidence 

that foliar treatments are worthwhile. 

Foliar sprays are protectants and 

should be targeted against small 

seedlings before downy mildew 

becomes well-established in the crop. 

Main picture: Downy Mildew on 

young plant cotyledon. 

Downy Mildew Hyaloperonospora parasitica (previously Peronospora parasitica)

GREY MOULD 

Common name: Grey Mould 

Pathogen: Botryotinia fuckeliana (asexual stage Botrytis cinerea) 

Host range 

Botrytis has a very wide host range. 

Disease development is usually 

associated with predisposing 

factors such as scorch or damage to 

foliage, adverse growing conditions 

or wet weather at flowering. 

Symptoms 

Brown soft rots or leaf spots with 

tufts of grey sporulating fungal 

growth are the most common 

symptoms. Scorch caused by frost, 

chemical or fertilisers are rapidly 

colonised by grey mould and a 

progressive rot develops unless 

conditions are sufficiently dry for 

the infected tissues to dry out. Stem 

15 

rots during stem extension and 

flowering are often associated with 

nitrogen fertiliser scorch. Stem 

lesions are white to greyish brown 

and can be difficult to distinguish 

from sclerotinia stem rot unless 

grey mould is sporulating on the 

lesion. Grey leaf spots and more 

extensive leaf rots occur where 

petals adhering to the foliage 

enable grey mould to become 

established. The leaf lesions may 

show concentric zones and be 

difficult to distinguish from target 

spots caused by Alternaria spp. 

Individual pods may be completely 

covered in sporulating grey mould. 

This is usually associated with

16 

GREY MOULD 

damage from pests such as bladder 

pod midge. 

Disease Cycle 

Air-borne spores of the grey mould 

pathogen are ubiquitous. It is 

present in decaying plant residues 

within the crop and surrounding 

areas. It can develop rapidly given 

favourable warm and wet or humid 

conditions. Flowers are frequently 

colonised and fallen petals develop 

grey mould whilst on the leaves or 

on the ground. 

Importance 

Grey mould can cause some loss of 

plants when it affects the stem. 

There may be significant losses if 

scorch to the crop has been severe. 

Losses are small if only a few 

scattered plants or pods are affected. 

In the north and Scotland, leaf 

damage is considered important. 

Control 

Many of the commonly used 

fungicides have useful activity 

against grey mould. Fungicide 

treatments applied for sclerotinia at 

early to mid-flowering give useful 

control. 

Photographs: (Main) Botrytis with leaf lesion associated with floral parts. 

Botytis on plant stem.

Grey Mould 

Botryotinia fuckeliana (asexual stage Botrytis cinerea) 

GREY MOULD 

17

18 

LIGHT LEAF SPOT 

Common name: Light Leaf Spot 

Pathogen: Pyrenopeziza brassicae (asexual stage Cylindrosporium concentricum) 

Hosts 

Light leaf spot is primarily a disease of 

brassicas including oilseed rape, and a 

range of vegetable and forage crops. 

Symptoms 

The first symptoms are usually large 

mealy blotches on the leaves with a 

pinkish white centre and white spore 

droplets around the edge of the 

lesion. Symptom expression varies 

with environmental conditions and 

cultivar. On heavily infected plants, 

lesions can affect a large proportion 

of leaf area causing distortion and 

stunting and early senescence. The 

white centres are easily confused 

with damage caused by nitrogen 

fertiliser scorch or frost. The 

former usually has a very sharply 

defined margin to the lesion. Frost 

and wind damage both produce 

silvering symptoms, and frost 

damage can make light leaf spot 

symptoms more conspicuous. Field 

distribution of symptoms may help 

diagnosis as light leaf spot often 

occurs in distinct patches or foci 

with the mostly severely affected 

plants at the centre of the patch. 

Where symptoms are indistinct it is 

helpful for diagnosis to look for 

light leaf spot sporulating on the 

youngest leaves and flower buds 

during the winter. Incubation of 

leaves with suspicious symptoms 

for 1-2 days in a polythene bag at 

ambient temperatures (dry them

first if they are very wet) helps 

diagnosis as new white spore 

droplets form around lesions 

(Note: recently sprayed crops may 

not produce new sporulation). 

Symptoms can appear in young 

plants in September, but generally 

few are found in commercial crops 

until late November or December 

in England. The disease develops 

extensively over winter and heavily 

infected plants may be killed during 

cold frosty weather. In the spring, 

severely affected plants are 

stunted and produce weak stem 

extension growth. 

Secondary spread of light leaf spot 

occurs throughout the life of the 

crop and elongated black or 

pinkish black lesions form on 

stems. Heavily infected leaves often 

remain attached to the stem much 


19 

longer than unaffected leaves. 

Affected pods may be curled and 

distorted with pinkish brown 

discolouration or carry faint lesions 

producing white spore pustules. 

Stem lesions usually have black 

speckling around the lesions and 

have a less sharply defined margin 

than Phoma stem lesions. The two 

may occur together in the same 

lesion. Stem lesions developing on 

early stem extensions often show 

horizontal cracking as extension 

growth occurs. 

Life cycle 

Crop residues producing air-borne 

ascospores in early autumn are the 

main source of inoculum for new 

crops. Early sown crops tend to 

show more disease than later 

sowings. Seed-borne infection does 

occur and may be important when 

the crop is grown in new areas. 

Leaf spots are produced by 

ascospores and then secondary 

spread occurs by means of splash 

dispersed conidia produced in 

acervuli on leaf lesions during the 

life of the crop. Some conidia may 

be dispersed to nearby crops. 

Ascospores are produced in small 

black apothecia on dying or dead 

leaves in spring may contribute to 

disease development on the upper 

leaves and pods along with splash 

dispersed conidia. 

Infection can progress internally 

within the plant following infection 

in the autumn and it may 

subsequently appear on buds 

before they emerge in the spring.

20 


Infection requires free water and a 

minimum of 6 hours of leaf 

wetness. Maximum efficiency of 

infection occurs at within 48 hours 

of wetness duration. The latent 

period ranges from 14 days at 15°C 

to about 30 days at 4°C. The 

pathogen is inhibited by high 

summer temperatures (>20°C). It is 

able to grow at low temperatures 

and is most damaging when fungal 

growth at the growing point occurs 

whilst plant growth has stopped. 

A prediction model of light leaf 

spot severity in spring has been 

used successfully for many years. It 

is based on disease levels on the 

pods pre-harvest and summer 

temperatures and can be found on 

the Rothamsted and CropMonitor 

websites. 

Importance 

Light leaf spot can cause severe 

yield loss (>50%) when plants are 

stunted and killed during the 

winter. It is most damaging in 

Scotland and northern England, 

but problems can occur in 

susceptible varieties in all regions. 

The estimated yield loss is 

calculated as 33% x % plants 

affected at the early stem extension 

stage (ie if 15% plants are affected, 

the yield loss is expected to be 5%). 

Control 

In high risk areas, varieties with 

good resistance to light leaf spot are 

essential. Oilseed rape stubbles 

should be cultivated or ploughed 

prior to emergence of new crops. 

Azole fungicides are recommended 

to control light leaf spot 

but their effectiveness may be 

diminished by strains of light leaf 

spot with reduced sensitivity to 

these fungicides. Where light leaf 

spot occurs regularly, a spray is 

applied in autumn (November/early 

December) and followed by a 

second treatment at early stem 

extension. Further treatment maybe 

required to protect the pods if the 

disease is still active at flowering. 

In southern, eastern and central 

England, fungicides applied to 

control phoma are likely to give 

control of light leaf spot. 

Photographs: (Main) Light leaf spot on upper leaf. Light leaf spot on 

stem in crop.


Light Leaf Spot Pyrenopeziza brassicae (asexual stage Cylindrosporium concentricum) 

21

22 

PHOMA LEAF SPOT AND STEM CANKER, BLACKLEG 

Common name: Phoma Leaf Spot and Stem Canker, 

Blackleg 

Pathogen: Leptosphaeria maculans (asexual stage Phoma A - Phoma lingam) 

Leptosphaeria biglobosa (asexual stage Phoma B - Phoma lingam). 

Hosts 

Leptosphaeria maculans has 

numerous races, defined in the case 

of oilseed rape by their virulence 

gene content. New races can emerge 

within 3 years of introducing 

varieties with a new single major 

resistance gene. They may affect 

other Brassica species, including 

forage and vegetable types. The 

variation in Leptosphaeria 

biglobosa is not well understood; it 

also occurs in oilseed rape and 

other Brassicas. 

Symptoms 

Pale brown, white or greenish 

leaf spots (5–20 mm diameter) are 

the most common symptom of 

L. maculans (also referred to as 

Phoma A leaf spots) on leaves. The 

underside of the lesion is usually 

green. Leaf spots contain scattered 

dark fruiting bodies (pycnidia) that 

ooze deep pink spore masses. Leaf 

spots occur mainly on the older 

leaves, some spots may have a 

yellow halo and produce browning 

of the leaf veins. The severity of leaf 

spot is very variable, ranging from 

single lesions to over 50% leaf area 

affected. Infection can occur soon 

after emergence on cotyledons and 

this can result in early stem infection 

and death of seedlings. On old 

yellow leaves, Phoma leaf spots may 

form green islands.

Leptosphaeria biglobosa produces 

small dark leaf spots (2-10 mm 

diameter), also known as Phoma B 

type leaf spots that have few 

pycnidia and an irregular shape. 

These are easy to confuse with 

symptoms of dark leaf spot 

(Alternaria spp.) and larger lesions 

overlap in appearance with some 

Phoma A type lesions on resistant 

varieties. Where varieties have 

major gene resistance that prevents 

L. maculans from producing leaf 

lesions, all the leaf spots may be 

Phoma B lesions. 

The pathogen grows down the leaf 

veins and petiole and invades the 

stem often up to harvest. 

Stem base symptoms (cankers) 

appear about 6 months after the first 

leaf symptoms and are sunken brown 


23 

lesions associated with the leaf scars 

at the stem base. These lesions 

usually have pycnidia present. The 

cankers gradually enlarge and may 

girdle and weaken the stem base 

causing premature ripening and 

lodging. On mature plants, canker 

lesions cause blackening of the roots, 

woody tissues and pith at the stem 

base. When stem infections occur at a 

late stage (January/February) cankers 

remain small. Phoma stem lesions 

occur higher up the stem and are the 

result of infection of leaves (on 

extending stem or secondary to insect 

pest damage). Pod symptoms are 

common and are typically brown 

lesions with pycnidia and a black 

margin. Infection of flowering shoots 

may lead to clusters of dead flower 

buds with pycnidial lesions on the 

pedicels, flower buds and upper stem.

24 


When the crop senesces and 

immediately after harvest, extensive 

phoma development occurs on the 

stubble. Large white or grey 

spreading lesions can be found with 

numerous pycnidia. These gradually 

disappear as wet weather post 

harvest leads to a transition from the 

asexual stage (pycnidia) to the sexual 

stage (black pseudothecia) on the 

stems and roots. 

Cankers and stem lesions are 

produced by L. biglobosa, but are 

generally considered less damaging 

than those caused by L. maculans. 

Both species often occur in mixtures 

on the same plant and are only 

distinguishable in the laboratory. 

Life cycle 

For L. maculans, the disease cycle is 

considered monocyclic with airborne 

ascospores produced in the 

previous year’s oilseed rape stubble 

introducing disease into new crops 

during autumn and winter. 

Pycnidiospores produced on leaf 

spot and stem lesions are thought to 

be of little importance in the 

epidemic. The onset of leaf spotting 

varies from year to year and depends 

mainly on rainfall in August and 

September. Rainfall is important for 

ascospore maturation on stubble. 

Early epidemics occur when there is 

frequent rainfall (> 20 days) in 

August and early September. Dry 

conditions delay maturation of 

air-borne species and hence the 

appearance of leaf spotting in crops. 

Predicted dates for crops reaching a 

threshold of 10% plants affected 

are available on the Rothamsted 

website. Ascospores require a 

minimum of 4 hours leaf wetness for 

infection but infection rates increase 

when leaf wetness periods are longer. 

Leaf spot symptoms appear after an 

accumulated mean temperature of 

120 degree days (ie 5 days at 20ºC, 

30 days at 4ºC). 

Plant size is an important factor in 

the development of stem cankers as 

the pathogen grows from leaf spots 

down the petiole to the stem. At low 

temperatures, this may be only 

1mm per day and stem infection 

takes longer where plants have large 

leaves compared with plants that 

have small leaves. Early leaf infection 

leads to early stem cankers and 

is most damaging to yield. Late 

leaf infection (e.g. December) is 

important when it occurs on small 

plants, but may not cause yield loss in 

crops with large plants. The 

appearance of cankers and their 

progressive increase in severity with 

time are influenced by cultivar 

resistance. Stem cankers cause yield 

loss when more than 50% of the 

stem circumference is girdled. 

Pod symptoms may lead to infection 

of the seeds, though such symptoms 

are not a reliable guide to the level of 

seed-borne infection.

Importance 

Phoma stem canker is the most 

damaging disease of winter oilseed 

rape in the UK and occasionally 

causes problems in spring oilseed 

rape. Problems are most likely to 

occur in southern, eastern and central 

England. On susceptible cultivars, 

(resistance ratings 4 or 5) yield losses 

are about 0.5-0.7 t/ha under high 

disease pressure. Losses on more 

resistant varieties (resistance ratings 

greater than 7) are generally smaller. 


Phoma Leaf Spot and Stem Canker, Blackleg 

Leptosphaeria maculans (asexual stage Phoma A - Phoma lingam) 

Leptosphaeria biglobosa (asexual stage Phoma B - Phoma lingam). 

25 

Control 

Strategies for control involve 

cultivations to bury crop residues 

before the emergence of new crops, 

use of resistant varieties and azole 

fungicide sprays in autumn and early 

winter. Both L. maculans and L. 

biglobosa are commonly seed-borne 

and seed treatments are targeted 

against them. 

Pictures: (main) Phoma leaf spot on upper leaf surface. Small stem canker 

lesion at the stem base.

26 

PHYTOPHTHORA ROOT ROT 

Common name: Phytophthora Root Rot 

Pathogen: Phytophthora megasperma 

Hosts 

Phytophthora megasperma is 

usually the pathogen involved. It is 

likely to affect a range of crucifers 

and possibly other species, but 

most problems relate to brassicas. 

Symptoms 

Problems are not usually noticed 

until leaves of plants turn reddish 

purple and plants wilt and die 

during the winter or early spring. 

Patches of affected plants often 

occur in waterlogged areas on 

headlands or in wet or poorly

drained fields. The tap root is 

severely rotted and has a pale 

brown colour and a distinctive 

strong brassica smell. Plants are 

easily pulled out of the ground or 

lie on the soil surface when the 

roots have rotted away. 

In spring, affected plants fail to grow 

away at the early stem extension 

stage and usually die. Late or mild 

infection can cause premature 

ripening or early death of plants that 

have apparently grown normally 

and produced seed pods. 

Life cycle 

P. megasperma is a soil-borne 

pathogen, surviving by means of 

resting spores (oospores). High soil 

moisture favours infection and 

Phytophthora Root Rot 

Phytophthora megasperma 


27 

problems are associated with poor 

drainage or compacted and waterlogged 

patches. Temperatures of 15 

– 25ºC are optimal for infection. 

The pathogen may be spread by 

flood water and by movement of 

soil on machinery during field 

operations. 

Importance 

Severe attacks have been uncommon. 

Some problems have ocurred on sites 

which also have clubroot so that the 

extent of phytophthora problems 

may be underestimated. 

Control 

It may be necessary to improve 

drainage and extend rotations 

where problems are occurring. 

Main picture: Phytosphthora root rot - white mycellium appeared after 

incubation.

28 

POWDERY MILDEW 

Common name: Powdery Mildew 

Pathogen: Erysiphe cruciferarum 

Hosts 

Powdery mildew is common in 

winter and spring oilseed rape, 

particularly in the south and east of 

England. It occurs in specialised 

races with cross infection between 

oilseed rape and other Brassica 

species, though interactions with 

other crucifers are less certain. 

Symptoms 

Small, circular white colonies of 

radiating fungal growth are the most 

common symptoms on leaves, stems 

and pods. The number of colonies 

can increase rapidly to give almost 

complete cover of aerial plant parts. 

Colonies may cause some leaf 

yellowing in localised blotches or 

more extensively. Powdery mildew 

affects both the upper and lower leaf 

surfaces and tends to be more severe 

on the underside of the leaves 

especially in autumn. When 

conditions are less favourable for its 

development, colonies are greyish or 

there is mainly fine black speckling 

of the affected leaves. 

Life cycle 

The disease cycle is dependent on the 

survival of powdery mildew on green 

host tissue and dispersal of air-borne 

conidia. It occurs commonly on 

volunteers after harvest and in 

autumn it is most prevalent in earlysown 

crops with large vigorous 

plants. There is a sexual stage of 

brown or black cleistothecia that is 

not often seen. Disease severity 

declines over-winter, but crops 

affected in the autumn are usually 

the first to show symptoms in

the spring or summer. Rapid 

development can occur from the late 

flowering stage onwards in winter 

oilseed rape and from flowering 

onwards in spring oilseed rape. 

Severe infection is most common in 

spring oilseed rape and severity can 

reach 100% cover of stems, leaves 

and pods. 

There is very large variation in the 

occurrence of powdery mildew from 

year to year. It developed early in 

flowering in 2007 in a warm spring, 

but showed very limited activity in 

2008 after a cooler autumn and 

winter. 

Importance 

Powdery mildew usually develops 

late in the season in winter oilseed 

rape and causes little damage. In 

autumn, only forward crops are 

badly affected and this may even be 

Main picture: Powdery Mildew on underside of leaf. 

Powdery Mildew Erysiphe cruciferarum 


29 

beneficial if it restricts foliar growth. 

In France, it can be damaging on 

spring oilseed rape, though little 

work has been done in the UK to 

quantify losses. Very heavy infection 

in spring oilseed creates high levels of 

dust at harvest and fungicidal 

control measures may be beneficial 

for improved harvesting operations. 

Control 

Fungicides applied for Sclerotinia 

control during flowering may have 

some effect on powdery mildew, but 

usually lack the persistence to give 

very effective control up to the end of 

June. Crops that retain green tissue 

late in the season are often more 

severely affected than early maturing 

crops. Hence fungicide treatments 

may appear to aggravate powdery 

mildew.

30 

RING SPOT 

Common name: Ring Spot 

Pathogen: Mycosphaerella brassicicola 

Host 

There is some specialisation within 

the ring spot pathogen, but field 

observations suggest there can be 

spread from kale and other 

brassicas to oilseed rape. 

Symptoms 

Leaf spots range in size from a few 

millimetres to 2.5cm in diameter 

and occurs from autumn onwards. 

The first symptoms are small dark 

lesions that increase in size and may 

be angular and delineated by the 

larger leaf veins. Sometimes they 

have a yellow margin. Numerous 

tiny black fruiting bodies are 

produced within the leaf lesions, 

initially these are pycnidia and later 

pseudothecia that produce 

ascospores. Both types of fruiting 

body are smaller and more 

numerous than the pycnidia found 

within phoma leaf spots, so leaf 

lesions are often grey. Phoma and 

ring spot are difficult to distinguish 

and a low incidence of ring spot is 

often overlooked. Ring spot can 

also cause large black spots on the 

pods, very similar to those of 

Alternaria and white leaf spot. 

Ring spot also produces more 

greenish lesions on pods with 

numerous small black fruiting

odies. It can cause early leaf loss 

when there are numerous spots on 

leaves, but it is uncommon for ring 

spot to be severe. 

Life cycle 

The cycle of ringspot is dependent 

on air-borne ascospores produced 

in brassica crop residues or on the 

oldest leaves within the crop. The 

spores produced by pycnidia in the 

leaf spots are not infective. It may 

be seed-borne, but this is likely to 

be of little importance. Only a few 

hours of leaf surface wetness or 

very high humidity are required for 

infection to occur; periods of 

several days with rain are required 

for heavy infection to occur. Leaf 

spot appears 10-14 days after 

Main Picture: Ring Spot on upper sides of crop. 

Ring Spot Mycosphaerella brassicicola 

RING SPOT 

31 

infection at temperatures of 15- 

20ºC. Oilseed rape is most likely to 

be affected where vegetable 

brassicas or strips of kale used for 

game cover are nearby. 

Importance 

Ring spot is a problem where 

brassicas are grown year-round, 

particularly near the coast. It is 

rarely damaging in oilseed rape. 

Control 

Where fungicides used are to 

control phoma, light leaf spot and 

sclerotinia, azole products may well 

provide useful control of ring spot. 

Resistance to MBC fungicide has 

been recorded in ring spot from 

vegetable brassicas.

32 

SCLEROTINIA STEM ROT; WHITE MOULD 

Common name: Sclerotinia Stem Rot; White Mould 

Pathogen: Sclerotinia sclerotiorum 

Hosts 

A wide range of broad-leaved crops 

and weeds are susceptible including 

oilseed rape, potatoes, dwarf beans, 

carrots, celery, lettuce, peas and 

spring field beans. Note winter field 

beans are affected by the related 

species Sclerotinia trifoliorum. 

A third species, Sclerotinia minor 

also occurs in the UK but has not 

yet been reported in oilseed rape. 

Symptoms 

The first leaf and stem lesions are 

most commonly seen during 

flowering, usually soon after petals 

are observed to be sticking to 

leaves. The leaf lesions are pale 

brown or white, often centred on 

an adhering petal and gradually 

enlarging in size. White stem 

lesions develop along stems, often 

originating from leaf petioles. 

Young lesions have a water-soaked 

leading edge. More advanced 

lesions will encircle stems, 

destroying all underlying tissue and 

white fluffy mycelium, along with 

immature white and mature black 

sclerotia, can be found inside the 

stem. When conditions are humid, 

white mycelium and sclerotia are 

produced on the outside of the stem 

lesions. The position of lesions on 

the stem may be a useful guide to 

when infection occurred. Lesions at 

the base of the main stem usually 

occur at the early flowering stage or 

possibly from leaf infection during 

the winter. The latter occurs from 

late autumn onwards and is usually 

associated with vigorous early 

sown crops that have large 

numbers of dead leaves present. 

Stem lesions may be large and 

extend from the lower stem 

downwards into the taproot and 

upwards so that the smaller 

branches are affected. The smaller 

branches may also have discrete 

white lesions that do not contain 

sclerotia because of the small 

volume of rotted tissue.

Premature plant death can occur 

and severely infected stems are 

brittle and break easily, increasing 

crop lodging. Severe infection can be 

seen as “whiteheads” against the 

backdrop of healthy, green crop 

from the end of flowering onwards. 

Plants that die during pod-filling 

become progressively blackened as 

sooty moulds develop on them. 

There are various causes of 

premature ripening and careful 

diagnosis is required to distinguish 

Phoma stem canker, botrytis, 

phytophthora root rot and 

verticillium wilt from sclerotinia 

stem rot. 

Life cycle 

The pathogen overwinters as 

sclerotia in soil and crop debris, and 

can survive for over 10 years when 

buried in soil. The sclerotia are very 

variable in size and shape (1-20mm) 

depending on the size of the host 

plant and where they are produced. 

Sclerotia may be introduced into 

fields in seed. Occasionally plant 

infection may take place directly 

from infected crop residues or by 

mycelial spread from sclerotia. After 

a period of cold conditioning during 

the winter, sclerotia mainly germinate 

in moist soils at temperatures above 

10°C to produce saucer shaped 

fruiting bodies (apothecia). 

Apothecia are pale brown in colour 

and 5-15mm in diameter. They 

liberate air-borne ascospores, during 

drying conditions. Wet weather may 


33 

reduce ascospore dispersal if the 

apothecia become flooded with 

water. Ascospores are dispersed 

within the crop or field where they 

are produced, but may spread to 

nearby fields if they can escape from 

the crop canopy. Ascospores land on 

petals, leaves, pods and stems, but 

require exogenous nutrients to 

enable them to germinate and infect 

oilseed rape plants. Petals and other 

flower parts are the main nutrient 

source. Senescent plant tissues and 

damage (eg hail) may also enable 

sclerotinia to become established. 

A key part of the disease cycle is 

weather that leads to petals sticking 

firmly to the foliage. Light rain is 

most likely to give good petal 

sticking whilst heavy rain can reduce 

disease risk when petals are washed 

off the leaves. In Germany, guidance 

of sclerotinia risk is provided by 

SkleroPro which uses an infection 

period requiring at least 23 hours

34 


with 80% relative humidity at 

temperatures above 7ºC. Once 

petals have stuck to the foliage 

plants becomes infected within 24 

hours, though stem lesions usually 

become evident 10-14 days later. 

Stem infection can occur directly in 

the leaf axil or from leaf lesions that 

spread down the petiole. Stem 

lesions increase in size girdling the 

stem and extending up and down 

the stem. The diagnostic sclerotia 

are produced most commonly inside 

infected stems. These are harvested 

along with the seed or returned to 

the ground, providing more 

inoculum along with those present 

in stem bases and roots. 

Secondary spread can occur within 

crops when an infected plant is in 

direct contact with other plants. 

This is most apparent in lodged 

crops where sclerotinia mycelium 

quickly spreads from stem to stem. 

Pods may be affected, particularly in 

lodged crops. Some spread via the 

roots may also occur. The sclerotia 

present in the top 5-7.5 cm of the 

soil germinate and produce 

apothecia in the following year. 

Sclerotia buried deeply can remain 

dormant for many years and will 

germinate when brought near the 

soil surface. 

Importance 

Yield losses of over 50% (>2 t/ha) 

have been reported in severely 

affected fields. Average losses 

nationally have been 1-2% in recent 

years, but widespread epidemics in 

2007 and 2008 caused losses of 3- 

4%. Once occurring every few

years, stem rot has recently started 

to increase in severity and frequency 

across the country. Its importance 

should be considered for the whole 

rotation because of its persistence in 

soil and its ability to affect many 

other crops in the rotation. 

Control 

Epidemics are difficult to predict. 

Decisions are based mainly on the 

history of the disease on the farm 

and the forecasts of unsettled 

weather at flowering that could lead 

to petal sticking. Fungicides have 

almost entirely protectant activity, 


Sclerotinia Stem Rot; White Mould Sclerotinia sclerotiorum 

35 

but can provide very effective control 

when applied just before infection 

takes place. Two sprays may be 

required at high risk sites to protect 

the crop throughout flowering. 

Sclerotia may be deeply buried by 

ploughing down after problems in 

oilseed rape, but should not be 

brought back to the soil surface in 

future years. Biological control 

agents such as the fungus 

Coniothyrium minitans (as 

Contans) can be applied as a spray 

of spores that parasitise and kill 

the sclerotia. 

Photographs: (Main) Sclerotinia young lesion. Sclerotinia in oilseed rape 

stem and apothecia produced in a sclerotinia monitoring grid.

36 

SOOTY MOULDS 

Common name: Sooty Moulds 

Pathogen: Alternaria spp, and Cladosporium spp. 

Hosts 

Alternaria and Cladosporium are 

ubiquitous on dead plant residues. 

Symptoms 

Grey and black fungal colonies 

develop on scorched, senescent 

or dead plant tissues and can 

produce large quantities of 

powdery black spores. They are 

often seen discolouring white 

blotches on leaves caused by 

nitrogen fertiliser scorch. At crop 

maturity, prematurely ripened 

plants show blackening. Scattered 

black plants may indicate severe 

stem disease caused by Sclerotinia 

stem rot or stem canker. Blackening 

may sometimes be limited to a few 

pods damaged by pests. In wet 

seasons when harvesting is delayed, 

swathed and standing crops can be 

completely blackened. If aphid 

infestations produce honeydew, 

sooty moulds develop on the sticky 

exudates.

Life cycle 

Air-borne spores from dead foliage 

within the crop or part of general 

air spora provide inoculum of these 

moulds. Development occurs very 

rapidly in warm and wet weather. 

Photo: Sooty mould, close-up on pods 

Sooty Moulds 

Alternaria spp, and Cladosporium spp. 

SOOTY MOULDS 

37 

Importance 

The sooty moulds are generally of 

minor importance as the affected 

plants or pods are already dead 

from other causes. Sooty moulds 

may cause allergic reactions in 

sensitised individuals and suitable 

precautions against dust should be 

taken at harvest.

38 

VERTICILLIUM WILT 

Common name: Verticillium Wilt 

Pathogen: Verticillium longisporum 

Hosts 

Whilst this is primarily a pathogen 

of brassicas and cruciferous weeds, 

a range of other weed and crop 

hosts may contribute to its survival. 

Symptoms 

In tests under controlled conditions, 

affected seedlings may show stunted 

or reduced growth. In the field, the 

first symptoms are not usually 

evident until flowering when leaves 

may show yellowing of half the leaf. 

This is not always a reliable 

symptom. As the plants reach 

maturity, yellow or brown 

discoloration, of one side of the stem 

or branches occurs and extends 

from the stem base to the upper 

branches. The proportion of the 

stem circumference affected by this 

vertical stripe varies from narrow 

stripes of about 10% up to 100%. 

Beneath the stripe, there is grey 

discoloration of the vascular tissue. 

This becomes more obvious as the 

outer fleshy tissues of the stem 

dehydrate during ripening. The 

branches into which the verticillium 

extends ripen prematurely and the 

proportion of the plant affected 

reflects the proportion of the 

circumference affected. 

At harvest, affected plants are 

distinguished by the grey colour of 

their stems where the microsclerotia 

are produced. The root system and 

pith of affected plants are also grey. 

Verticillium wilt is difficult to 

identify when Phoma stem canker is 

present, as that also produces black 

or grey lesions, brown stripes on 

stems and premature ripening.

Phoma lesions are usually only a 

few centimetres long and do not 

extend up the entire length of the 

main stem. Phoma lesions also have 

distinctive pycnidia producing deep 

pink spore exudate, which is a key 

aid to their diagnosis. Phoma and 

verticillium infections often occur 

on the same plant. 

Life cycle 

In autumn, soil-borne microsclerotia 

initiate most infection in winter 

oilseed rape. The pathogen colonises 

the root system only at this stage and 

it only spreads to the vascular system 

and the upper plant during stem 

extension. This takes place by means 

of conidia produced in the xylem 

that form new colonies higher up 

the stem. Disease development is 

favoured by early sowing and warm 

spring temperatures. It is more likely 

to be damaging to yield when there 

are high temperatures and drought 

stress pre-harvest. As the plant 

matures, numerous microsclerotia 

are produced outside the vascular 


39 

tissues, giving the grey discolouration 

late in June. These microsclerotia will 

produce new soil inoculum as 

infected plant residues break down. 

Microsclerotia are capable of long 

term survival in soil. It may be 

seed-borne or carried as a 

contaminant (eg in soil or plant 

fragments) in seed. 

Importance 

In the UK, badly affected crops 

have shown considerable premature 

ripening and this suggests yield loss is 

occurring. This has not been 

quantified in the UK, but in Sweden 

losses may be as high as 50%. Most 

problems are associated with several 

years of short rotations of oilseed rape 

and have occurred mainly in southern 

and central England. 

Control 

Longer rotations of at least 1 in 4 years 

are currently the only available control 

measure as there are no resistant 

varieties or fungicide treatments. 

Pictures: (Main) Verticillium with close-up on upper stem. 

(Overleaf) Verticillium with in crop causing premature ripening.

40 


Verticillium Wilt Verticillium longisporum

VIRUS DISEASE 

Common name: Cauliflower Mosaic 

Pathogen: Cauliflower mosaic virus (CaMV) 

Host 

The host range of CaMV is mainly 

cruciferous species and a few of the 

Solanaceae. It commonly affects 

vegetable brassicas and also occurs 

in oilseed rape, forage brassicas and 

related weeds. 

Symptoms 

Leaf symptoms include vein 

banding and a yellow green mosaic. 

On maturing oilseed rape plants it 

can cause black spotting or streaks 

CAULIFLOWER MOSAIC 

41 

on the stems and pods. These 

symptoms may be confused with 

dark pod spot. Severely affected 

plants may be stunted and show 

twisting and distortion of the pods. 

Symptom expression is influenced 

by the variety and the presence of 

other viruses. 

Life cycle 

CaMV is transmitted in a 

non-persistent or semi-persistent 

manner by aphids, particularly the 

mealy cabbage aphid (Brevicoryne 

brassicae) and the peach potato 

aphid (Myzus persicae). The main 

source of the virus is likely to be 

nearby brassica crops and kale used 

for game cover. Whilst infection 

can occur throughout the life of the 

crop, infection early in the autumn 

is likely to be most damaging. 

Importance 

The incidence of CaMV has been 

very low in oilseed rape. Only 

occasionally are patches of infected 

plants apparent. 

Control 

Specific control measures for this 

virus disease with insecticides are 

rarely required.

42 


Cauliflower Mosaic 

Cauliflower mosaic virus (CaMV) 

Main picture: Cauliflower mosaic virus

VIRUS DISEASE 

Common name: Turnip Mosaic 

Pathogen: Turnip mosaic virus (TuMV) 

Host 

TuMV has a very wide host 

range including species in the 

Chenopodiaceae, Compositae, 

Leguminosae and Solanaceae as 

well as the Brassicaceae. Some 

strains are host specific. 

Symptoms 

Leaf symptoms are more severe 

than those of CaMV. It can produce 

both local and systemic mosaics and 

TURNIP MOSAIC 

43 

necrotic spotting. In some cases, it 

may cause plant death. It may occur 

in mixture with CaMV. 

Life cycle 

TuMV is transmitted mechanically 

and in a non-persistent manner by 

many aphid species. In oilseed 

rape, the mealy cabbage aphid 

(Brevicoryne brassicae) and the 

peach potato aphid (Myzus persicae) 

are the most important vectors. The 

main source of the virus is likely to 

be nearby brassica crops and kale 

used for game cover. Whilst 

infection can occur throughout the 

life of the crop, infection in the 

autumn is likely to be most 

damaging. It is not thought to be 

seed-borne. 

Importance 

The incidence of TuMV has been 

very low in oilseed rape, though it 

continues to cause problems in 

vegetable brassicas. 

Control 

Specific control measures with 

insecticides are rarely required for 

this virus disease.

44 

TURNIP MOSAIC 

Turnip Mosaic 

Turnip mosaic virus (TuMV) 

Picture: Turnip mosaic virus (TuMV) damage in field causing severe 

stunting.

VIRUS DISEASE 

Common name: Turnip Yellows 

Pathogen: Turnip yellows virus (TuYV) 

Host 

This virus was previously known as 

Beet western yellows virus but the 

name has been recognised as 

Turnip yellows virus since 2002, 

based on its host range and 

inability to infect sugar beet. 

It affects oilseed rape, other 

brassicas and a number of common 

weeds such as chickweed, field 

pansy, field speedwell, groundsel 

and Shepherd’s-purse. 

Symptoms 

The presence of the virus is difficult 

to detect by visual inspection as it is 

TURNIP YELLOWS 

45 

often symptomless. Leaf symptoms 

include reddening towards the leaf 

margins and, from stem extension 

onwards, interveinal yellowing and 

a strong purplish-red colouring. 

These symptoms may be confused 

with ‘stress’ symptoms caused by 

adverse growing conditions or 

nutrient deficiencies. In controlled 

inoculation studies, the virus causes 

stunting and reduced branching. 

Life cycle 

TuYV is transmitted in a persistent 

manner by aphids, but they do not 

pass the virus to their progeny. The

46 

Turnip Yellows 


most important vector is the peach 

potato aphid (Myzus persicae). The 

aphid can acquire the virus in as 

little as 15 minutes and be able to 

transmit it 1-4 days later after 

feeding for 10-30 minutes. The 

main sources of the virus are likely 

to be nearby brassica crops, 

volunteers and weeds. Whilst 

infection can often be detected at 

high levels in the autumn, further 

spread can occur during the winter 

if mild weather allows aphids 

to remain active. Aphids leaving 

winter oilseed rape in spring carry 

the virus to spring oilseed rape 

and other susceptible hosts. TuYV 

is not transmitted mechanically or 

via seed. 

Main photo courtesy of Brooms Barn. 

Turnip yellows virus (TuYV) 

Importance 

TuYV is an important disease in 

oilseed rape, though its incidence 

does show considerable regional 

and year-to-year variation. Losses 

of 10% may not be uncommon and 

severe infection may reduce yields 

by 25%. 

Control 

Insecticides applied as seed 

treatments or as foliar sprays are 

available to control the aphid 

vector, but when there are large 

numbers of viruliferous aphids, 

good control is difficult to achieve 

because virus transmission occurs 

rapidly.

WHITE BLISTER OR WHITE RUST 

Common name: White Blister or White Rust 

Pathogen: Albugo candida 

Host 

White blister has occurred on spring 

turnip rape in Scotland. It commonly 

affects vegetable and forage 

brassicas and various ornamental 

species, but has not been found on 

swede rape types of winter or spring 

oilseed rape (Brassica napus). The 

weed Shepherd’s-purse is commonly 

affected, but carries a race that does 

not affect brassica crops. Downy 

mildew is often found colonising 

shoots with white blister. 

Symptoms 

Raised white pustules are produced 

mostly on the underside of leaves. 

These may be single or clustered. 

They gradually discolour with age 

47 

and become brown. The leaf may 

be distorted where pustules occur 

and yellowing develops on the 

upper surface. Systemic infection 

can develop in flower shoots and 

‘staghead’ symptoms which are 

twisted, distorted racemes with 

heavy pustule production. Downy 

mildew may occur in association 

with white blisters. 

Life cycle 

The disease may be initiated from 

soil-borne oospores that germinate 

to produce swimming spores 

(zoospores) that move in soil water 

or are splash dispersed to infect 

seedlings. Sporangia produced in 

the white blisters are wind-dispersed

48 


within and between crops. These 

may be the main source of inoculum 

where brassica production is 

intensive. Infection requires several 

hours of surface moisture and 

symptoms appear in about 10 days 

at the optimum temperature of 

20ºC. Infection of the flowering 

meristem results in distorted 

flowerheads. Oospores form in 

infected tissues particularly in 

‘stagheads’ and these contaminate 

seed and soil at harvest. 

Main picture: White blister on Kale 

White Blister or White Rust 

Albugo candida 

Importance 

To date, white blister has only 

affected a few crops of turnip rape 

in Scotland. 

Control 

Grow swede rape types in 

preference to turnip rape where 

problems have occurred. 

Fungicides are available for white 

blister control in vegetable 

brassicas, so new options might be 

developed in future.

WHITE LEAF SPOT 

Common name: White Leaf Spot 

Pathogen: Mycosphaerella capsellae 

(asexual stage Pseudocercosporella capsellae) 

Hosts 

This pathogen affects a range of 

brassicas and cruciferous weeds. 

Symptoms 

The most diagnostic symptoms are 

large circular white leaf spots 

(10-20 mm diameter), often with a 

brown margin. The centre of the 

lesion is white with some dark 

reticulation and a dark central spot. 

Young lesions are irregular greyish 

or dark spots (1-2 mm), again with 

darker reticulation. Symptoms are 

likely to be confused with downy 

mildew and the two may occur 

together. Leaf symptoms are found 

49 

from autumn onwards. Susceptible 

varieties may show extensive stem 

infection, most of the upper stem 

becomes grey, a symptom known as 

“grey stem”. The pods are also 

affected, showing small brown 

lesions with dark reticulation and 

developing into large blotches with 

reticulation (reminiscent of net 

blotch lesions on barley). 

Life cycle 

Spread to new crops of oilseed rape 

occurs in autumn by means of airborne 

ascospores produced on 

residues of the previous crops or 

weed hosts. Secondary spread by

50 


splash-dispersed conidia leads to 

further spread within the crop. 

Only 6-8 hours of leaf wetness are 

required for infection at 15-20ºC. 

Symptoms appear after 

accumulated mean temperature 

reaches 120 degree days (ie 8 days 

at 15ºC). At stem extension, heavy 

rainfall is required to splash spores 

from the infected basal leaves to the 

upper plant. Crops can therefore 

grow away from the disease if the 

weather is not conducive to splash 

dispersal at stem extension. Seed 

transmission may occur. 

Main picture: White leaf spot, oilseed rape leaf. 

White Leaf Spot 

Mycosphaerella capsellae (asexual stage Pseudocercosporella capsellae) 

Importance 

It is mainly a disease of the south 

and west in England, but there have 

been occasional reports in the east. 

Severe infection is uncommon, but 

leaf, stem and pod infection is 

capable of causing yield loss. 

Control 

Azole fungicides give good control 

and specific treatment may be 

required when leaf symptoms are 

common.

SOURCES OF DISEASES TABLE 1 

TABLE 1: Sources of diseases 

Disease Seed Crop residues Volunteers/Other crops/OSR/Veg Soil Water spread 

Clubroot (★) ★★ ★★★ ★★ 

Damping off ★★★ ★ 

Dark leaf and pod spot ★ ★★★ ★★ 

Downy mildew (★) ★★★ ★ 

Grey mould ★★ ★★ 

Light leaf spot (★) ★★★ ★★ 

Phoma canker ★ ★★★ 

Phytophthora ★★★ ★★ 

Powdery mildew ★★★ 

Ring spot ★★★ 

Sclerotinia ★ ★ ★★ ★★★ 

White leaf spot (★) ★★★ ★★ 

Verticillium wilt (★) ★★★ 

Virus Diseases 

Turnip Yellows ★★★ 

Cauliflower mosaic ★★★ 

Turnip mosaic ★★★ 

KEY 

★★★ : Most important source 

★★ : Important 

★ : Minor importance 

(★) : Possible, but usually minor significance 

51

52 

TABLE 2 COMPONENTS OF DISEASE CONTROL 

TABLE 2: Components of Disease Control 

Disease Rotation Variety Seed treatment Fungicide sprays Sow date 1 

Clubroot ★★★ ★★ ★ L 

Damping off ★ ★★ ★E 

Dark leaf and pod spot - (★) ★ ★★★ ★L 

Downy mildew ★ ★ ★ ★ ★E 

Grey mould ★ 

Light leaf spot ★★★ ★★★ ★ L 

Phoma canker ★★ ★ ★★★ ★ E 

Phytophthora ★★ 

Powdery mildew (★) ★ ★L 

Ring spot ★ 

Sclerotinia ★★ (★) ? ★★★ 

White leaf spot (★) ★★ 

Verticillium ★★★ (★) L 

Insecticide 

Virus diseases: Seed Spray 

treatment 

Turnip Yellows ★ ★★★ ★L 

Cauliflower mosaic ★ ★★ ★ 

Turnip mosaic ★ ★★ ★ L 

KEY 

(★) : Differences may be noticed 

★★★ : Major factor 

★★★ : Important factor 

★ : Minor factor 

1 Reduced disease risk with early (E) or later (L) sowing

PERIODS FOR THE CONTROL OF KEY DISEASES WITH FOLIAR SPRAYS TABLE 3 

TABLE 3: Periods for the control of key diseases with foliar sprays 

(Highlighted in yellow) 

Disease Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul 

Downy Mildew 

Phoma leaf spot and stem 

canker 

Light leaf spot 

Sclerotinia stem rot 

Grey mould (Botrytis) 

Dark pod spot (Alternaria) 

White leaf spot 

53 

Turnip Yellows

54 

Glossary 

GLOSSARY 

A 

Anamorph The imperfect or asexual stage of a fungus 

Apothecium A cup- or saucer-like ascocarp, which produces ascospores 

e.g. in Sclerotinia 

Acervulus A tiny cushionlike or blisterlike structure produced by certain 

fungi on a plant host and consisting of a mass of hyphae-bearing 

asexually produced spores. 

Asexual Without sex organs or sex spores: vegetative 

Ascocarp A fruiting body which bears asci 

Ascospores Sexually produced spores contained within an ascus 

Ascus (pi. asci) A sac-like cell which contains the products of the sexual 

stage (teleomorph) as ascospores (generally 8) 

B 

Biotroph An organism entirely dependent upon another living organism 

(the host) as a source of nutrients 

Bract Leaves on the upper stems of oilseed rape that lack petioles 

Break crop A crop (e.g. oilseed rape) grown in rotation with other crops 

(e.g. wheat) to improve the growing conditions of the following crop 

C 

Chlamydospore An asexual spore arising from a hyphal segment, a 

resting stage 

Chlorosis The yellowing of normally green plant tissue 

Cleistothecia The closed spherical ascocarps of the powdery mildews 

Conidia Asexual fungal spores formed from the end of a conidiophore 

Conidiophore A specialised hypha on which one or more conidia are 

produced 

Cotyledons The seed leaves or part of the embryo that forms the primary 

leaf 

D 

Damping-off Disease of plant seedlings caused by seed- or soil-borne 

fungi 

Dicotyledon A flowering plant whose embryo has two cotyledons (seed 

leaves) 

Direct drilling The drilling of seed into ground (usually stubbles) which 

has received minimal or no cultivation

GLOSSARY 

E 

Epidemic A widespread increase in the incidence of an infectious disease 

Epidermis The outermost layer of cells of an organ, usually only one cell 

thick 

F 

Focus (plural : foci) A site of local concentration of diseased plants, usually 

about a primary source of infection or coinciding with an area originally 

favourable to disease establishment 

Forma specialis f. sp A group within a pathogen species that can only 

infect particular hosts 

G 

Gall Abnormal plant growth usually localised and swollen and caused by 

various pathogens or pests 

H 

Honeydew A sticky secretion produced by aphids. 

Host A living organism harbouring a pathogen 

Host specific Pertaining to a particular host, generally species specific 

Hypha One of the filaments of a mycelium 

I 

Immune Cannot be infected by a given pathogen 

Inoculum Micro-organisms or virus particles which act as a source of 

infection 

Inflorescence The group or arrangement in which flowers are borne on a 

plant 

Internode Part of a plant stem between two successive nodes 

L 

Lamina The blade of the leaf 

Lesion A localised area of diseased tissue 

Lodging When a standing crop is caused to lean or bend due to adverse 

weather or soil conditions 

55

56 

GLOSSARY 

M 

Microsclerotium (plural microsclerotia) Tiny resting bodies (just visible to the 

naked eye) composed of aggregations of pigmented cells e.g. Verticillium 

Minimal cultivation A reduced form of cultivation 

Morphology The form and structure of an organism 

Mosaic A pattern of disease symptoms on a plant apparent as 

green/yellow or dark/light areas, usually referring to virus infections 

Mycelium The mass of hyphae forming the body of a fungus 

N 

Necrotroph Micro-organism feeding only on dead organic tissue 

Node The level of a stem at which one or more leaves arise 

O 

Oospore A resting spore that is the sexual stage of Oomycete fungi 

including downy mildews, Pythium and Phytophthora 

P 

Pathogen An organism which causes disease 

Pedicel Flower or pod stalk 

Perithecium An ascocarp shaped like a flask containing asci 

Petiole The leaf stalk 

Plasmodium An amoeba-like stage of the clubroot pathogen 

Primary inoculum Spores or fragments of mycelium capable of initiating 

disease 

Pseudothecium A perithecia-like structure with a single cavity containing 

ascospores 

Pustule A spore mass developing below the epidermis and then breaking 

through at maturity 

Pycnidium Flask shaped fruiting body with an apical pore lined internally 

with pycnidiospores 

Pycnidiospores Spores formed within a pycnidium 

Raceme Compound flowering head of oilseed rape 

R 

Resistance The inherent capacity of a host plant to prevent or reduce the 

development of a disease

GLOSSARY 

S 

Saprophyte An organism deriving its nutrients from dead or decaying 

tissue of another organism 

Sclerotium (plural sclerotia) Compact mass of fungal hyphae e.g. Sclerotinia, 

capable of being dormant for long periods, and giving rise to fruiting bodies or 

mycelium 

Senescence The dying process of a plant or plant part 

Sporangiophore A hypha or fruiting structure bearing spores 

Sporangium A container or case of asexual spores. In some cases it 

functions as a single spore 

Spore A reproductive unit in fungi 

Sporulation The period of active spore production 

Susceptible Non-immune i.e. capable of becoming infected by a pathogen 

Systemic Growth or movement within the plant, may be symptomless for 

some pathogens 

T 

Telomorph The sexual or so-called perfect growth stage or phase in fungi 

Tolerance the ability of a plant host to sustain the effects of a disease 

without dying or suffering serious injury or crop loss 

V 

Vascular The conductive tissue of plants comprising xylem and phloem 

Vector An organism capable of transmitting inoculum 

Virulence The ability of a pathogen to produce disease 

Volunteer Self-sown plant growing from shed seed 

W 

Whitehead Prematurely ripened ears of cereals or stems of oilseed rape 

often caused by pathogens attacking the roots or stem base 

Z 

Zoospore Asexual swimming spore e.g. clubroot, Pythium, Phytophthora 

57

58 

Drilling 

GROWTH STAGE 

SB BBCH TIMING 

Drilling Mid-August - end September 

Germination and Emergence 

SOWING 

Winter Oilseed Rape Growth Stage Guide 

The tables below show the Roger Sylvester-Bradley (SB) system of scoring 

oilseed rape growth stages and the equivalent stages in the BBCH system. 

Although many of the stages are the same, some like side shoot 

development are seen only in the BBCH guide while the Sylvester-Bradley 

system concentrates more on seed development than pod ripening. 

If you are recording or using crop growth stages it is important to check 

which system is being used. Plants can be described with more than one 

growth stage for example using the BBCH system a plant could be at both 

growth stage 29 (9 side shoots developed) and 23 (3 fully extended 

internodes). At least 50% of plants should be at the main growth stage 

recorded, though there is usually variability and the main range of growth 

stages should be noted as well. 


EMERGENCE 

0 Germination & 00 Dry seed Mid-August - end September 

emergence

ROSETTE FORMATION 

GROWTH STAGE 

Leaf Production and Emergence 

A leaf is usually counted when you can see its petiole. Growth stage is the 

number of leaves present PLUS the number of leaf scars from fallen leaves. 

This is also the ‘rosette’ stage and can run beyond 10 in the growth stage 

numbering. Leaf production stage is 1 in both systems, the number of 

developed leaves follow the comma in the Sylvester Bradley system or are 

the second digit in BBCH system. 


1,0 Cotyledons unfolded 10 Cotyledons late August - early October 

and green Completely unfolded 

1,2 Two true leaf unfolded 12 Two leaves unfolded late August - mid October 

(see picture) 

1,3 3 true leaves etc 13 

etc 

1,9 Ninth true leaf 19 Nine or more late October - late February 

unfolded leaves unfolded 

Two true leaves unfolded 

59

60 

GROWTH STAGE 

Stem Extension 

Stage 2 covers stem elongation in the Sylvester Bradley system. In the 

BBCH, Stage 2 is the number of side shoots and stage 3 the beginning of 

stem elongation. In both systems the second digit gives the numbers of side 

shoots or internodes visible. An internode is counted when the distance 

between leaves or leaf scars exceeds the stem diameter. Some stem 

extension can occur in autumn in early sown crops. It is useful to note 

plant height as well as the number of internodes. 


2,0 Stem elongation, 

no internodes 

30 Late February early March 

2,2 Two internodes March 

2,5 About 5 internodes 35 Mid to late March 

etc etc 

Mid stem extension (circa 10 internodes) 

STEM EXTENSION

GREEN BUD YELLOW BUD 

GROWTH STAGE 

Flower Bud Development 

Flower bud development in stage 3 in Sylvester-Bradley and stage 5 in 

BBCH. The sub stages are described by the second digit. 


3,0 Only leaf buds present 

3,1 Flower buds enclosed 50 late February - mid March 

by leaves 

3,3 Flower buds visible 53 mid March 

from above ‘green bud’ 

3,5 Flower buds raised above mid March - early April 

youngest leaves 

(= mid-stem extension 

when crop is >60cm tall) 

(see picture page 60 

and below) 

3,7 First flower buds yellow 59 mid-March - late April 

‘yellow bud’ 

Flower buds raised above youngest leaves 

61

62 

GROWTH STAGE 

Flowering 

Fully opened flowers are described in stage 4 of the Sylvester-Bradley 

system and stage 6 of BBCH. The second digit shows the proportion of 

flowers open within the crop. Records are often taken on the main raceme 

as secondary branching is variable between crops. Notes on the overall 

flowering status are useful, particularly at the end of flowering when the 

whole crop is becoming green. 


4,0 First flowers open 60 late March - early May 

4,1 10% flowers open 61 late March - early May 

4,2 20% flowers open 62 

4,4 40% flowers open 

4,5 50% flowers open on 

main raceme: ‘full flower’ 

or mid-flowering 

65 mid April - mid May 

4,9 90% flowers open on 

main raceme 

67 mid to late May 

First flowers open 

GREEN BUD YELLOW BUD

FLOWERING 

10% flowers open 

20% flowers open 

GROWTH STAGE 

63

64 

GROWTH STAGE 

50% flowers open on main raceme: ‘full flower’ 

FLOWERING

FLOWERING 

Late flowering, 90% of flowers open on main raceme. 

GROWTH STAGE 

65

66 

GROWTH STAGE 

Pod development 

Pod development is stage 5 using Sylvester-Bradley and 7 in BBCH. The 

second digit shows the proportion of pods developed. As with flowering 

this is most useful for the main raceme. Pods are included when they are 

at least 2cm long. Score both flowering and pod development up to the end 

of flowering when seed development is the key stage to record. 


5,1 10% pods developed 71 10% pods have 

reached final size 

5,5 50% pods developed 71 10% pods have 

(see picture) reached final size 

5,9 All pods developed 79 Nearly all pods mid May - early June 

reached final size 

50% pods developed 

POD DEVELOPMENT

POD DEVELOPMENT 

GROWTH STAGE 

Seed development and ripening 

Seed development is covered by stage 6 using Sylvester-Bradley, and in 

BBCH mainly by stage 8. These two measurements are conflated in stage 

8 of the BBCH system. Check pods on the lower third of the main raceme 

to determine seed development and colour. 


6,1 Seeds present Mid May - early June 

6,2 Most seeds translucent 

but full size 

6,3 Most seeds green 79 Mid to late June 

6,4 Most seeds green-brown 81 Late June - early July 

mottled 

6,8 Most seeds black and hard 85 Mid July - early August 

6,9 All seeds black 89 

and hard 

Seeds green filling pod cavity 

Stem Senescence 

Stage 8 in Syslvester Bradley assesses stem ripening. This is not generally 

used. 


8,5 Half stems green 95 Late June - early July 

67

68 

GROWTH STAGE 

Pod senescence 

The ripened pods are described in stage 9 of Sylvester Bradley and stage 8 

of BBCH (see previous page). In both systems the plants reach stage 99 at 

harvest. 


9,1 Most pods green 79 June 

9,5 Half pods green 85 Late June -early July 

Plant dead and dry 97 July 

9,9 Harvest 99 Mid July - mid August 

Beginning of ripening most seeds green. 

POD DEVELOPMENT

POD DEVELOPMENT 

Pod ripening 

GROWTH STAGE 

69

70 

Harvest 

GROWTH STAGE

Photo Library 

Clubroot (Plasmodiophora brassicae) 

Right: Oilseed Rape. Left: Shepherd’s-Purse. 

Clubroot disease in oilseed rape 

CLUBROOT 

71 

Photo Library

72 

Rhizoctonia root lesion 


Damping Off, Rhizoctonia Root Rot 

(Pythium spp./Rhizoctonia solani / Thanatephorus cucumeris) 

Rhizoctonia seedling damage

Dark Leaf and Pod Spot 

(Alternaria brassicae and Alternaria brassicicola) 

Alternaria on lower leaf surface 

Alternaria on upper leaf surface 


73 

Photo Library

74 

Alternaria on pods 

Alternaria on pod 

DARK LEAF AND POD SPOT

Alternaria on upper leaf surface 

Alternaria + white leaf spot 


75 

Photo Library

76 

DOWNY MILDEW 

Downy Mildew 

(Hyaloperonospora parastica) (previously Peronospora parasitica) 

Downy mildew on upper leaf 

Downy mildew on cotyledon

Downy mildew on underside of leaf 

Downy mildew. Severe damage on oilseed rape cotyledons 

DOWNY MILDEW 

77 

Photo Library

78 

GREY MOULD 

Grey Mould (Botryotinia fuckeliana (asexual stage Botrytis cinerea) 

Botrytis on plant stem 

Botrytis leaf spot

Botrytis with leaf lesion associated with floral parts 

Leaf Botrytis in crop 

GREY MOULD 

79 

Photo Library

80 


Light Leaf Spot 

(Pyrenopeziza brassicae /Cylindrosporium concentricum) 

Light leaf spot (close-up) 

Light leaf spot - note bleached spots and white spore droplets

Light leaf spot on leaf 

Light leaf spot on leaf - note cracking and white spore droplets 


81 

Photo Library

82 


Light leaf spot on upper leaf 

Light leaf spot on stem

Light leaf spot on stem in crop 


83 

Photo Library

84 


Light leaf spot on stem - infected leaves are still attached

Light leaf spot on pod (close-up) 

Light leaf spot on pods 


85 

Photo Library

86 


Phoma Leaf Spot and Stem Canker, Blackleg 

(Leptosphaeria maculans(asexual stage Phoma A – Phoma lingam) 

(Leptosphaeria biglobosa (asexual stage Phoma B – Phoma lingam) 

General stem diseases 

Verticillum Wilt, Stem Phoma and Sclerotina


Healthy stem on left - range of canker severities from slight to severe 

87 

Photo Library

88 


Underside of leaves showing Phoma and Alternaria damage 

Transverse section of OSR stem showing disease

Phoma canker in autumn crop 

Phoma stem lesions 


89 

Photo Library

90 


Phoma stem lesions (various) 

Phoma on upper side of leaf

Phoma on underside side of leaf 

Phoma leaf spot (of leaf) 


91 

Photo Library

92 

Phoma pod spot 

PHOMA LEAF SPOT AND STEM CANKER, BLACKLEG

Phoma spore ooze on stem lesion 


93 

Photo Library

94 


Phoma stem lesions in crop

Phoma upper stem lesion 

Phoma leaf spot on upper leaf surface 


95 

Photo Library

96 


Small stem canker lesion at the stem base


Fruiting body on stubble Leptosphaeria maculans (pseudothecium) 

97 

Photo Library

98 


Phytophthora Root Rot 

(Phytophthora megasperma) 

Phytophthora root rot - white mycellium appeared after incubation

Powdery Mildew 

(Erysiphe cruciferarum) 

Powdery Mildew on oilseed rape stem 

Powdery mildew on leaves in autumn 


99 

Photo Library

100 


Powdery mildew on leaf, stem and pod symptoms

Ring Spot 

(Mycosphaerella brassicicola) 

Ring spot on pods 

Ring spot on upperside of leaf 

RING SPOT 

101 

Photo Library

102 

RING SPOT 

Ring spot on underside of leaf 

Ring spot on leaf

Ring spot (close-up) 

RING SPOT 

103 

Photo Library

104 

SCLEROTINIA STEM ROT: WHITE MOULD 

Sclerotinia Stem Rot: White Mould 

(Sclerotinia sclerotiorum) 

Sclerotinia in Oilseed rape stem 

Petal stick - note recent yellow petals and older bleached petals

Close-up of sclerotinia stem lesion 


105 

Photo Library

106 


Sclerotinia group in crop

Sclerotinia premature ripening 

Sclerotinia spread in lodged crop 


107 

Photo Library

108 


Sclerotinia apothecia developing from sclerotia 

Sclerotinia young lesion

Apothecia produced in a sclerotinia monitoring grid 

Sclerotinia mycellium on leaves during the winter 


109 

Photo Library

110 


Sclerotinia, early damage from leaf infection in winter

Sooty Moulds 

(Alternaria spp, and Cladosporium spp.) 

Sooty mould, close-up on pods 

Sooty mould infection after sclerotinia 

SOOTY MOULDS 

111 

Photo Library

112 


Verticillium Wilt 

(Verticillium longisporum) 

Verticillium Wilt close-up on upper stem 

Verticilliium Wilt exposted with grey colour after vascular tissue is exposed

Verticillum Wilt in stubble - grey or black on stems 


113 

Photo Library

114 


Verticillium Wilt in stem section: note faint grey colour 

Verticillium Wilt scraped stem

Verticillium Wilt microsclerotia 

Verticillium Wilt in crop causing premature ripening 


115 

Photo Library

116 


Verticillium Wilt can cause yellowing of half of the leaf

VIRUS DISEASES - Cauliflower Mosaic 

(Cauliflower mosaic virus (CaMU) 

Cauliflower mosaic 


117 

Photo Library

118 


Cauliflower mosaic (CaMV) in oilseed rape crop

Cauliflower mosaic - leaf, stem and pod symptoms 


119 

Photo Library

120 

TURNIP MOSAIC 

VIRUS DISEASES - Turnip Mosaic 

(Turnip mosaic virus (TuMV) 

Turnip mosaic (TuMV) damage in field causing severe stunting

VIRUS DISEASES - Turnip Yellows 

(Turnip yellows virus (TuYV) 

Purple-leaved plant affected with TuY virus. 


Purple-leaved plant affected with TuY virus. (Photograph courtesy of Brooms Barn). 

121 

Photo Library

122 


White Blister or White Rust 

(Albugo candida) 

White blister on mustard upper leaf surface 

White blister on Shepherd’s-purse

White blister on kale 

White blister on stem. (Photograph courtesy of SAC). 


123 

Photo Library

124 


White blister on kale

White Leaf Spot 

(Mycosphaerella capsellae/Pseudocercosporella capsellae) 

White leaf spot, oilseed rape leaf 

White leaf spot on leaves 


125 

Photo Library

126 WHITE LEAF SPOT 

White leaf spot on pods (Photography courtesy of Alan Inman and Rothamstad Research) 

White leaf spot on pods

Reference Material and Further Reading 

Useful sources of information 

HGCA varieties guide: 

www.hgca.com/content.template/23/0/Varieties/Varieties/Varieties%20Home% 

20Page.mspx" 

HGCA fungicide tools: 

www.hgca.com/content.output/878/878/Resources/Tools/ 

HGCA Fungicides and dose response curves: 

www.hgca.com/content.output/3215/3215/Crop%20Research/Fungicide%20p 

erformance%20data/Winter%20Oilseed%20Rape.mspx 

CropMonitor: Disease surveys and monitoring: 

www.cropmonitor.co.uk/wosr/wosr-intro.cfm 

Light leaf spot disease forecast: www3.res.bbsrc.ac.uk/leafspot/ 

Phoma forecasting: www.rothamsted.bbsrc.ac.uk/ppi/phoma/index2.html 

Sclerotinia monitoring: www.totaloilseedcare.co.uk 

HGCA Sclerotinia deision guide: 

www.hgca.com/minisite_manager.output/2995/2995/Sclerotinia%20Decision% 

20Guide%20Tool/Sclerotinia%20Decision%20Guide%20Tool/Decision%20G 

uide.mspx?minisiteId=24 

Aphid monitoring: www.rothamsted.ac.uk/insect-survey/ 

Oilseed crop canopy size and management: www.totaloilseedcare.co.uk 

BASF product and general information: www.agriCentre.basf.co.uk 

Books 

Fitt B D L, Evans N, Howlett B J and Cooke B M (Eds). 2006. Sustainable 

strategies for managing Brassica napus (oilseed rape) resistance to 

Leptosphaeria maculans (phoma stem canker). Dordrecht, The Netherlands: 

Springer. (reprinted from European Journal of Plant Pathology Volume 114 

Issue 1, 2006). 

Rimmer S R, Shattuck V I and Buchwaldt. L (Eds) 2007.: Compendium of 

Brassica Diseases. St Paul, MN: APS. 

127

128

Disclaimer 

ADAS and BASF plc, Crop Protection have provided funding for 

this publication. While the authors have worked on the best 

information available to them, neither the ADAS nor BASF plc 

shall in any event be liable for any loss, damage or injury 

howsoever suffered directly or indirectly in relation to the 

Encyclopaedia or the research on which it is based. 

Reproduction of material 

No part of this publication may be reproduced, stored in or 

introduced into a retrieval system, or transmitted, in any form, 

or by any means (electronic, mechanical, photocopying, 

recording or otherwise), without the prior permission of the 

publishers. Requests for permission should be directed to ADAS 

and/or BASF plc, Crop Protection. 

£15.00

the encyclopaedia of oilseed rape diseases - BASF Crop Protection ...

Create successful ePaper yourself

Delete template?

Save as template?