a guide to the recognition and understanding of ramularia and other ...

A GUIDE TO 

THE RECOGNITION AND 

UNDERSTANDING OF 

RAMULARIA AND OTHER 

LEAF SPOTS OF BARLEY 

The Chemical Company

Introduction 

INTRODUCTION 1 

Ramularia, or more fully ramularia leaf spot, is the common name for the 

barley disease caused by the fungus Ramularia collo-cygni. 

The disease was first recorded in 1893, but it is only in the last 15 years 

that it has become recognised as an economically important disease both 

in Europe, Argentina and New Zealand. The disease is however more 

widespread and in some regions remains under reported, since ramularia 

leaf spot symptoms are easily mistaken for other more common diseases or 

misidentified as physiological leaf spots. 

In some areas it is has become one of the key diseases threatening barley 

and therefore should be a key consideration when planning fungicide 

programmes. Nevertheless, there remains some confusion regarding its 

identification, particularly in areas where it currently occurs infrequently. 

The primary motivation for producing this guide is therefore to help with 

identification. The inclusion of photographs of ‘spots’ produced by a range 

of other factors will further help to distinguish ramularia in the field. 

Information on the background biology of this important disease is also 

included, which will add interest, as well as an appreciation of how best to 

approach its control. 

There is still more to learn about the epidemiology of ramularia leaf spot, 

but some advice is given on the current integrated control measures which 

can be taken to help limit the loss in yield and quality caused by ramularia, 

as well as physiological leaf spots. 

The production of this guide was a team effort bringing together the 

authors Simon Oxley, Neil Havis and Andy Evans of SAC together with 

Steve Waterhouse and Lindy Tonguç of BASF who edited and formatted it. 

The publication was funded by BASF and SAC. We hope you find it 

interesting and informative. 

Authors 

Simon Oxley Neil Havis Andy Evans Steve Waterhouse Lindy Tonguç

2 

Contents 

RAMULARIA 

Distribution 

Current distribution ......................................................................4 

Symptoms 

CONTENTS 

Future projection of risk in Europe ..............................................6 

Early stage ....................................................................................8 

Intermediate stage ........................................................................8 

Later stage ..................................................................................12 

Symptoms on stems and awns ....................................................16 

Seed ............................................................................................19 

Symptom appearance 

Tillering to flag leaf emergence....................................................20 

Post ear emergence ......................................................................20 

Life cycle 

Sources of infection ....................................................................22 

Asymptomatic (invisible) phase ..................................................22 

Symptomatic (visible) phase ........................................................23 

Spore dispersal ............................................................................24 

Secondary infection during the season ........................................25 

Secondary infection of leaves from airborne spores ....................25 

Asteromella production ..............................................................28 

Control measures 

Varietal resistance........................................................................31 

Seed health and seed treatments ..................................................31 

Foliar fungicides..........................................................................32 

- Timing ......................................................................................32 

- Choice ......................................................................................34 

- Resistance ................................................................................35

Contents 

PHYSIOLOGICAL LEAF SPOTS 

CONTENTS 3 


Effect of light stress ....................................................................36 

Effect of variety ..........................................................................36 

Interaction with ramularia leaf spot ......................................................41 

Physiological leaf spots and pollen scorch ..............................................43 

Physiological leaf spots in response to disease attack ............................44 

Control of physiological leaf spot 

Variety ........................................................................................46 

Nutrition ....................................................................................46 

Activity of fungicides ..................................................................49 

DISEASES CAUSING SIMILAR SYMPTOMS TO RAMULARIA LEAF SPOT 

Net blotch ..................................................................................50 

Pyrenophora leaf stripe ..............................................................52 

Halo spot ....................................................................................53 

Septoria nodorum ......................................................................54 

Glossary ................................................................................................55 

References and further reading ..............................................................56 

Acknowledgements ................................................................................58

4 

RAMULARIA LEAF SPOT DISTRIBUTION 

Ramularia leaf spot distribution 

Ramularia leaf spot caused by the 

fungus Ramularia collo-cygni is 

recognised as an economically 

important disease of barley in 

Europe, South America and New 

Zealand. The fungus has been 

reported on other grass species and 

also on maize and is likely to be more 

widely distributed in regions where 

barley is not grown or where 

ramularia leaf spot is not recognised 

to be a serious threat to barley. 

The disease has been reported 

throughout Europe and these 

maps show the countries where 

ramularia leaf spot was first 

reported on barley in Europe and 

throughout the world. 

First reported outbreaks of ramularia leaf spot in Europe 

Worldwide distribution of ramularia leaf spot and Ramularia collo-cygni


The potential distribution of the disease has been mapped using climate 

matching software. These maps are based on the optimum weather 

conditions for Scotland, where the disease is established as an important 

economic disease. 

It shows the potential for the disease to become established in most 

European countries including countries around the Black Sea where no 

official outbreaks have been confirmed. 

Regions in Europe where weather conditions are suitable for ramularia leaf spot 

In the southern hemisphere, New Zealand is at risk from ramularia leaf 

spot and the disease is well established in that region. The disease has also 

been reported in the New South Wales region of Australia. 

Regions in Australia & New Zealand where weather conditions are suitable for ramularia leaf spot 

5

6 


The world map based on the potential distribution of the disease shows the 

greatest risk from ramularia leaf spot to be Europe, New Zealand, 

Argentina and the east and west coast of Canada. This distribution links 

well with known outbreaks, but the disease is more widespread in North 

and South America suggesting the pathogen can adapt to different 

climates. 

Regions where weather conditions are suitable for ramularia leaf spot 

Since seed movement is an important method of spreading the fungus, 

there is a real threat that ramularia leaf spot will become endemic in these 

regions if barley is grown. 

If new populations of the fungus develop which enable the fungus to adapt 

to new environments, the regions where the disease could become 

economically important will increase further. 

Future projection of risk in Europe from ramularia leaf spot 

Using a climate change forecast based on medium greenhouse gas 

emissions, the disease has the potential to remain a problem in the same 

countries in 2050, but the distribution within those countries can change. 

A greater threat will come from changes in the pathogen, which could lead 

to new races developing which can adapt to climate change or enable the 

disease to spread to other barley growing regions.

Projected distribution of ramularia leaf spot in 2050 

RAMULARIA LEAF SPOT DISTRIBUTION 7

8 

Early stages 

SYMPTOMS 

What are the symptoms of ramularia leaf 

spot on barley leaves? 

At the earliest stage of symptom development, small brown irregular 

“pepper spots” appear on the leaf. These are just visible to the naked eye. 

At this very early stage, the symptoms can be indistinguishable from 

physiological leaf spots caused by high light. However, ramularia leaf spots 

will be visible on both sides of the leaf, unlike physiological leaf spots 

which are more superficial and only visible on the side of the leaf exposed 

to the light. 

Intermediate stage 

The early “pepper spot“ symptom of ramularia quickly develops into 

typical ramularia leaf spot lesions. Look for rectangular dark brown 

lesions typically 2 mm x 0.5 mm in size. They have straight longitudinal 

sides where the lesions are defined by the leaf ridges. The shorter sides of 

the lesions are more irregular. At the centre of the brown lesions there is 

the darker brown centre where the original “pepper spot” symptom 

occurred. The whole brown rectangular lesion is surrounded by a yellow 

(or chlorotic) halo. This in turn is surrounded by a normal green leaf at 

this intermediate stage. 

Distinctive features of ramularia leaf spot lesions are that they are easily 

seen both on the upper and lower surface of the leaf and the longitudinal 

edges of the brown lesion remain enclosed by the leaf ridges.

Pepper spot symptom of ramularia leaf spot alongside distinctive rectangular symptoms. 


SYMPTOMS 9

10 

SYMPTOMS 


Classic ramularia leaf spot symptoms surrounded by pepper spot symptoms

Classic ramularia leaf spot lesions on upper side on leaf 

Classic ramularia leaf spot symptoms on underside of the same leaf 

SYMPTOMS 11

12 

Later stage 

SYMPTOMS 

The rectangular lesions remain visible on the upper and lower side of 

the leaf but the leaf dies back rapidly losing all its green leaf initially 

turning yellow (chlorotic) before dying back completely. This die-back 

usually starts to occur at the leaf tip. On the underside of the dead leaf, 

translucent spores of Ramularia collo-cygni develop in lines coming 

out from the leaf pores (stomata). These spores are not associated with 

the dark rectangular lesions which will still be visible on the dead 

leaves. The translucent spores can be seen using a magnifying hand 

lens or occasionally by the naked eye. Wet conditions late in the season 

can lead to a red colouration around ramularia leaf spot lesions on 

dead leaves. 

Later stage of ramularia leaf spot

Later stage of ramularia leaf spot on the underside of the same leaf 

Later stage of ramularia leaf spot showing loss of green leaf area at leaf tip 

SYMPTOMS 13

14 

SYMPTOMS 

Extensive ramularia leaf spot symptoms on leaf surrounded by dead leaf 

Extensive ramularia leaf spot symptoms on leaf surrounded by dead leaf

Spores of Ramularia collo-cygni on the underside of a barley leaf 

Spores of Ramularia collo-cygni on the underside of a barley leaf (Scanning electron micrograph) 

SYMPTOMS 15

16 

SYMPTOMS 

Ramularia leaf spot symptoms on stems and awns 

Ramularia leaf spot lesions also appear on the awns and leaf sheaths on 

barley stems. The dark brown rectangular lesions are small when 

compared to leaf symptoms, but they also comprise dark brown 

rectangular flecks surrounded by a yellow halo. The lesions continue to 

remain visible after the awns and leaf sheaths have died-back. 

Ramularia leaf spot on flag leaf and leaf sheath

Early stage of ramularia leaf spot on flag leaf surrounded by green leaf 

Later stage of ramularia leaf spot on flag leaf with no green leaf remaining 

SYMPTOMS 17

18 

SYMPTOMS 

Ramularia leaf spot symptoms on flag leaf and awns

Ramularia leaf spot on seed 

SYMPTOMS 19 

It is uncommon to recognise typical ramularia leaf spot lesions on the 

seed. Seed is however an important source of infection of Ramularia 

collo-cygni. 

Ramularia collo-cygni is deep seated in the seed and cannot be identified visually

20 

SYMPTOM APPEARANCE 

When do symptoms of ramularia leaf spot 

appear in crops? 

Tillering growth stages to flag leaf emergence. 

At tillering growth stages (GS25-30), ramularia leaf spot symptoms can 

develop on lower leaves which are dying back naturally or as a 

consequence of crop stresses caused by either nutritional deficiencies 

(i.e. low nitrogen), weather (i.e. frosts) or leaf scorch from the 

application of agronomic inputs. It is unusual to see ramularia leaf spot 

symptoms develop on newly emerged leaves and the leaves of healthy 

unstressed crops. 

Post ear emergence 

When crops start to flower (GS61-69), ramularia leaf spot symptoms 

can start to appear on the top leaves. Exposure to sunlight is an 

important stress factor which leads to symptoms developing hence the 

incidence of ramularia leaf spot is higher on the top two leaves. 

Varieties which have an upright growth habit and crops which have low 

plant populations can show more symptoms lower down the canopy, 

primarily due to increased light. Thicker crops and varieties with 

prostrate leaves or ears can show fewer symptoms where the upper 

leaves, ears and awns provide shade to the lower canopy. 

The process of flowering is also an important natural stress factor 

where the plant mobilises nutrient reserves away from the leaves in 

order to provide greater resources for ear and grain development. 

Crops which have limited fertiliser inputs (i.e. crops grown for low 

nitrogen malting barley) will show ramularia leaf spot symptoms earlier 

than feed barley crops where nitrogen is less limiting. 

Early maturing varieties will also show symptoms earlier than later 

maturing varieties.

SYMPTOM APPEARANCE 21 

Flowering is an important natural stress factor which leads to development of ramularia leaf spot symptoms

22 

LIFECYCLE 

Disease lifecycle 

The causal fungus of ramularia leaf spot (Ramularia collo-cygni) was 

first reported in 1893 in Italy. The fungus has also been called 

Ophiocladium hordei, Ovularia hordei and Ramularia hordeicola in 

scientific literature. More recent work would suggest the fungus is a 

Mycosphaerella species. Although the name of the causal fungus is 

likely to continue to change, the common name of the disease is now 

recognised as ramularia leaf spot. 

Source of infection 

One of the sources of infection for ramularia leaf spot is the seed. This 

can not be identified visually, but its presence can be confirmed using 

molecular diagnostic tests. In regions where the disease is not common, 

seed is likely to be an important source of the disease. Movement of 

seed is therefore a potential method to spread Ramularia collo-cygni 

populations into new regions. Furthermore, populations which may be 

more aggressive pathogens or which may be resistant to fungicides 

could also be spread through seed movement. Although the testing of 

seed for Ramularia collo-cygni is not required as a statutory seed test, 

methods exist which can identify the fungus in seed. 

Other sources of infection include airborne spores coming from barley 

volunteers and grasses. A second fungal body known as asteromella also 

exists in stubble. The importance of this stage in subsequent infection 

and the production of new fungal populations are under investigation. 

Asymptomatic or invisible phase 

When seedlings start to emerge, Ramularia collo-cygni fungus will grow 

inside the plant and move into new leaves as they develop. The plants 

will however show no visible disease symptoms of ramularia leaf spot. 

During this phase of the disease the fungus co-exists with the plant host 

as an endophyte. The impact the fungus has on the plant during this 

symptomless phase is unknown. The existence of endophytes is 

common in nature, particularly in grasses and indeed, endophytes have 

been shown to be beneficial to the host plant in some situations.

Symptomatic or visible phase 

LIFECYCLE 23 

When leaves start to die-back either as a consequence of natural ageing, 

weather or nutritional stresses, changes occur in the fungus within the 

leaf, leading to the production of plant toxins, identified as rubellins, 

which contribute to symptom development. Rubellins belong to a 

group of closely related anthraquinoid metabolites (rubellin A, B, C and 

D). Rubellin D is closely linked to the formation of typical ramularia 

leaf spot symptoms and later to leaf death as it spreads out from the 

initial source of infection to the rest of the leaf. The overall result of 

rubellin D formation by the fungus is extensive and premature leaf 

death. Although there is more fungus inside the lower leaves compared 

to the upper leaves, more symptoms appear at the top of the crop 

canopy. This occurs because the rubellin D produced by the fungus is 

activated by light to trigger the production of reactive oxygen species. 

Plants grown under shading are known to produce fewer ramularia leaf 

spot symptoms than plants grown in natural light. Restricting light will 

however reduce both crop yield and grain quality.

24 

LIFECYCLE 

Spore dispersal 

Leaf wetness is an 

important factor in spore 

dispersal and the infection 

of barley from airborne 

spores. The duration of 

leaf wetness in the spring 

is linked to the severity 

of ramularia leaf spot 

symptoms which occur 

after flowering. This 

observation can be used as 

a method to forecast the 

potential risk of ramularia 

leaf spot. 

Water logging is an important stress factor for ramularia leaf spot 

Leaf wetness is important for infection and can be used to forecast disease risk

Secondary infections during the season 

LIFECYCLE 25 

When ramularia leaf spot symptoms are present in a crop, secondary 

infections can occur as spores are dispersed from infected leaves. 

Airborne dispersal of Ramularia collo-cygni spores is reliant on leaf 

wetness. This is more important than rainfall. Spores are dispersed into 

the air 24-48 hours after a prolonged period of leaf wetness of several 

hours. These airborne spores can lead to secondary infection of leaves 

and they infect leaves through leaf pores (stomata). The dispersed 

spores are also likely to colonise barley heads and awns and also grasses 

which are known to be a secondary host for the disease. It is not known 

if barley seed is infected primarily by the airborne spores or infected by 

the fungus developing inside the plants. 

Secondary infection of leaves from airborne spores 

Spore of Ramularia collo-cygni growing on leaf surface

26 

LIFECYCLE 

Infection of barley by Ramularia collo-cygni through stomata (leaf pore) 

Infection of barley by Ramularia collo-cygni through stomata (leaf pore)

Cross section of Ramularia leaf spot symptoms 

Clusters of Ramularia collo-cygni spores on leaf surface 

LIFECYCLE 27

28 

LIFECYCLE 

Ramularia collo cygni spore on distinctive curved conidiophore 

Asteromella production 

Ramularia collo-cygni produces a second type of spore known as 

asteromella. They develop late in the season on straw. The importance 

of this second spore body on the disease epidemic is not fully 

understood, but they are a potential source of secondary spores in 

stubble which can infect the following barley crop. They are also a 

potential method for the pathogen to reproduce sexually leading to the 

formation of new races which may adapt to changes in climate and 

fungicide usage.

Ramularia collo-cygni second spore body (asteromella) on straw 

LIFECYCLE 29 

The disease lifecycle of Ramularia collo-cygni is summarised in the 

next two figures. Current information suggests ramularia leaf spot is a 

polycyclic disease with seed as a primary source of infection and 

airborne spores creating further infections when the leaves are wet.

30 

Ramularia Ramularia concentration concentration from from 

spore spore trap trap (pgrams) (pgrams) 

30000 

30000 

25000 

25000 

20000 

20000 

15000 

15000 

10000 

10000 

LIFECYCLE 

5000 

Seed infection 

5000key 

source of 

infection 

0 

0 

1st May 

1st May 05 

epidemics Ramularia leaf spot and epidemics spore and spore movement 

Ramularia epidemics and spore movement 

Seed main 

Early spore dispersal 

Late spore 

source of 

linked to leaf wetness dispersal a source 25 

infection 

Winter leads – 

Spring 

to secondary 

Spore dispersal of seed– infection 

barley 

barley 

infection minor impact on 

disease 

disease epidemic but source 

of seed infection? 

20 

15th May 

15th May 05 

Ramularia spores 

Date Date 

Winter Winter barley barley Spring barley Spring barley 

29th May 

29th May 05 

12th June 12th 05 June 

Ramularia leaf spot epidemics and spore movement 

Ramularia lifecycle 

GS0 Ramularia 

seed-borne 

Seed treatments? 

GS75-83 Ramularia 

symptoms on heads 

and awns 

Asteromella 

spores on straw 

Ramularia leaf spot 

26th June 26th05 June 

10th July 10th 05July 

24th July 05 

24th July 

7th Aug 05 

7th Aug 

Ramularia lifecycle 

G10-13 Ramularia 

detectable by diagnostics 

but no visual symptoms 

Airborne spores disperse 

when leaves are wet 

GS65 Physiological and weather 

stresses lead to rubellin production 

by fungus. Symptoms appear when 

rubellin is activated by light 

21st Aug 05 

21st Aug 

15 

10 

5 

0 

GS25-30 

Ramularia spots 

on dying leaves 

% Leaf area infected 

GS25-30 

Fungicides can 

reduce later 

disease epidemic. 

GS45-49 

Is best timing to 

protect crops 

with fungicide 

Fungus detected inside 

leaves 2-4 weeks before 

symptoms appear. 

25 

20 

15 

10 

5 

0 

% Leaf area infected

CONTROL MEASURES 31 

Control measures for ramularia leaf spot 

Varietal resistance 

Varieties differ in their susceptibility to ramularia leaf spot symptoms. 

In the UK spring barley varieties which show low levels of ramularia 

leaf spot include Decanter, Belgravia and NFC-Tipple High levels of 

Ramularia collo-cygni fungus can be found in the seed and developing 

leaves of the variety Decanter. The mechanism for resistance may 

therefore be a matter of the host plant being able to tolerate or break 

down the rubellin toxins produced by the fungus. Spring barley 

varieties which are most susceptible include Cocktail, Optic and 

Forensic. Yield losses associated with the disease can be as high as 1.0 

tonne per hectare. In resistant varieties, yield losses are 0.1-0.2 tonnes 

per hectare. Average yield losses in Scotland for spring barley are 0.4 

tonnes per hectare which equates to a loss of £10 million per year. 

Winter barley varieties also show different levels of resistance or 

tolerance to ramularia leaf spot. The malting barley variety Pearl 

exhibits low levels of symptoms whilst Flagon and Cassata are more 

susceptible. The feed barley variety Retriever can also be classified as 

susceptible. 

Seed health and seed treatments 

It is advisable to sow seed with low levels of contamination of 

Ramularia collo-cygni, particularly in regions where the disease is not a 

major threat, since seed transmission is a real risk for spreading this 

disease. However finding seed which is completely free from the 

pathogen is rare, even in the east of England where the disease is not 

perceived to be a major disease threat. Choosing seed stocks with less 

than 1pg of DNA per 100ng of total DNA in regions where the disease 

has yet to become established is recommended in the absence of 

effective seed treatments. 

Although seed is an important source of infection, currently available 

seed treatments have little impact on the fungus.

32 

CONTROL MEASURES 

Foliar fungicide treatments 

Fungicide timing 

The optimum timing to protect barley from ramularia leaf spot is before 

leaf spot symptoms are visible on the upper leaves. This usually occurs 

after the crop has flowered. The timing of the treatment is likely to be 

compromised by the latest application timing of fungicides, since most 

fungicides cannot be applied to malting barley crops when the ear has 

emerged. Awns visible growth stage (GS49) is therefore the optimum 

timing to protect the crop. 

Impact of fungicide timing on Ramularia 

leaf spot epidemic and Yield 

Ramularia leaf Spot 

development (AUDPC) 

180 

160 

140 

120 

100 

80 

60 

40 

20 

0 

Untreated 

Area Under Disease Progress Curve and Yield 

GS25 

Fungicide Timings 

GS25 + GS37 GS25 + GS49 

Ramularia Yield T/la 

Earlier treatments applied at tillering or stem extension growth stages 

can have some influence on the eventual disease epidemic, but they are 

insufficient to provide effective reduction of ramularia leaf spot 

symptoms. These earlier timings are however important to protect crops 

from other barley diseases including powdery mildew, net blotch, rusts 

and rhynchosporium. 

7 

6.8 

6.6 

6.4 

6.2 

6 

5.8 

Yield T/ha

CONTROL MEASURES 33 

For low input crops on resistant varieties where a single treatment is 

typically applied, then a treatment at flag leaf emergence (GS39) is a 

compromise to eradicate early disease and protect the crop from ramularia 

leaf spot. In regions where rhynchosporium and ramularia are common, 

two applications of fungicides are required for effective disease control. 

Once symptoms have started to develop in a crop, no fungicide will 

provide effective control. 

GS25-30 treatment has some influence on later disease epidemic

34 

Fungicide choice 

CONTROL MEASURES 

GS49 treatment is optimum timing to protect crop from ramularia leaf spot 

It is recommended that a combination of at least two fungicides which 

both have activity against ramularia leaf spot is applied at the optimum 

timing of awns visible growth stage (GS49). This will achieve the best 

reduction in ramularia leaf spot and the most cost effective yield 

response, whilst minimising the risk of fungicide resistance developing. 

Triazole fungicides epoxiconazole or prothioconazole both show good 

activity against ramularia leaf spot. 

Succinate dehydrogenase inhibitor fungicides (SDHIs) are also very 

effective. Current examples include boscalid, which is co-formulated 

with epoxiconazole (Tracker ® ) and isopyrazam which is co-formulated 

with cyprodinil. New fungicides in this group are expected to be 

launched over the next few years. 

Chlorothalonil provides effective protection against ramularia leaf spot 

and also prolongs green leaf area. Since it has multisite modes of action, 

it remains an important component of a fungicide mixture to control 

the disease and reduce the risk of fungicide resistance developing.

Fungicide resistance 

FOLIAR FUNGICIDE TREATMENTS 35 

Ramularia 

leaf spot 

Strobilurins 

azoxystrobin - 

picoxystrobin - 

pyraclostrobin - 

trifloxystrobin 

Triazoles 

- 

epoxiconazole ** 

prothioconazole 

Other straight ais 

*** 

chlorothalonil *** 

cyprodinil 

Mixtures 

* 

azoxystrobin + chlorothalonil *** 

epoxiconazole + boscalid *** 

isopyrazam + cyprodinil *** 

prothioconazole + fluoxastrobin *** 

**** 

*** 

** 

* 

Excellent protection 

Good protection 

Moderate protection 

Low protection 

- No protection 

As with most diseases, ramularia leaf spot is not exempt from the risk 

of resistance to fungicides. Analysis of samples of Ramularia collo-cygni 

taken from around Europe show that resistance to strobilurin fungicides 

(Quinone outside Inhibitors), is widespread and they should not be 

relied upon to deliver control of ramularia leaf spot (e.g. azoxystrobin, 

fluoxastrobin, pyraclostrobin, trifloxystrobin, picoxystrobin). These 

fungicides may however be required in a fungicide mixture to control 

other biotic diseases including net blotch and brown rust. 

Resistance to Ramularia collo-cygni has not been found in other groups 

of fungicides, but the use of combinations of active ingredients is a wise 

precaution against its development.

36 

Physiological leaf spots 

Physiological leaf spots or abiotic leaf spots are common terms used to 

describe leaf spots for which there is no obvious association with a 

disease and their cause is not fully understood. Environmental 

conditions which may trigger physiological leaf spots include extremes 

of light, temperature, nutritional deficiencies or toxicity, pollutants and 

other crop stresses. Since ramularia leaf spot develops as a consequence 

of stresses on plants, it is common for ramularia leaf spot symptoms to 

develop alongside physiological leaf spots and for physiological leaf 

spots to be mistaken for ramularia leaf spots. 


What are the symptoms of physiological leaf spots on barley leaves? 

Physiological leaf spots caused by light stress 

Early stages of physiological leaf spots caused by light stress include 

small brown “pepper spots” surrounded by a yellow halo. Symptoms 

are visible on the part of leaves exposed to light. These spots can 

superficially resemble the early stages of ramularia leaf spot and it is 

normal for them to occur on the same leaf as ramularia leaf spots. 

Physiological leaf spots will be clearly visible on the side of the leaf 

exposed to the light, but shaded parts of the leaf including the underside 

of the leaf may appear normal. 

Effect of variety 


Symptoms of physiological leaf spots vary depending upon the variety. 

In some varieties they develop into regular brown spots or streaks 

which are confined by leaf veins and which are surrounded by a yellow 

halo. In others, they form brown irregular spots which are not confined 

by the leaf veins and which do not have a yellow halo. 

The reason why some varieties exhibit more physiological leaf spots 

than others is thought to be due to differences in the ability of a variety 

to produce superoxide dismutase enzyme. This enzyme produces 

antioxidants which absorb the harmful effects of superoxides, produced 

inside the plant as a consequence of prolonged exposure to sunlight.

Early development of physiological leaf spots 

Intermediate development of physiological leaf spots 

PHYSIOLOGICAL LEAF SPOTS 37

38 


Advanced development of physiological of spots

Physiological leaf spots on winter barley variety Amarena 

Physiological leaf spots on the spring barley variety Spire 

PHYSIOLOGICAL LEAF SPOTS 39

40 


Physiological leaf spots on the spring barley variety Century

PHYSIOLOGICAL LEAF SPOTS 41 

Interaction between ramularia leaf spot and physiological leaf spots 

Ramularia leaf spot symptoms and physiological leaf spots regularly 

occur at the same time, causing challenges in identification of the 

primary cause. Since the rubellin D produced by Ramularia collo-cygni 

activates reactive oxygen species, its presence can produce both 

ramularia leaf spot symptoms and also activate the production of 

physiological leaf spots. 

The severity and combination of symptoms of the complex is dependent 

on the susceptibility of a variety to physiological leaf spots. In the 

1980s, selecting against physiological leaf spots was not a high priority. 

The spring barley variety Chariot is an example of a variety which 

regularly developed physiological leaf spot symptoms. These were seen 

as a typical characteristic of the variety and were deemed to be 

unimportant. When ramularia leaf spot was initially recognised as a 

serious problem in the 1980’s, symptoms were regularly assumed to be 

of physiological origin in Germany and the UK. By contrast, in Norway, 

breeders screened out barley varieties which showed extensive 

physiological leaf spots. This meant commercial varieties grown in 

Norway tended to show typical ramularia leaf spot symptoms and 

physiological leaf spots were mostly absent. 

The spring barley variety Chariot exhibits effective resistance to 

powdery mildew but it is susceptible to ramularia leaf spot. Since the 

introduction of commercial varieties with the mildew resistance gene 

mlo coincided with an increase in ramularia leaf spot, it was suggested 

at the time that there was a linkage between mlo and ramularia leaf 

spot. This was shown not to be the case and the presence of mlo gene 

reduced the level of ramularia leaf spot, but did lead to an increase in 

physiological leaf spots. 

Commercial spring varieties introduced in the last ten years in the UK, 

including varieties the mlo genes for mildew resistance now show 

fewer physiological leaf spot symptoms compared to varieties used in 

the 1990s.

42 


Physiological leaf spots on spring barley variety Chariot 

Combination of ramularia leaf spot and physiological leaf spots

PHYSIOLOGICAL LEAF SPOTS AND POLLEN SCORCH 43 

Physiological leaf spots and pollen scorch 

A common name sometimes used to describe unknown leaf spots is 

"pollen scorch". Pollen can be associated with leaf spots, but this would 

be expected since many physiological leaf spots and ramularia leaf spots 

occur on the top leaves after flowering, when pollen is likely to be seen 

on affected leaves. Although there is little evidence to suggest that 

pollen on the leaf surface is a direct cause of these leaf spots, extensive 

leaf scorch can be associated with pollen on the leaf surface, particularly 

following wet spells of weather when pollen sticks to the leaves. In these 

situations, the growth of saprophytic fungi, bacteria and yeasts 

(microflora) on the leaf surface use pollen as an additional food source 

growing rapidly on the leaf surface. 

These microflora may cause leaves to die-back earlier than normal. Leaf 

surfaces are however complex environments for a wide range of 

mircroflora. Some of these are known to prevent infection from known 

plant diseases whilst others may enhance disease. Plant defence 

mechanisms can also respond to the presence of some of these leaf 

surface microflora causing localised leaf death in response to a potential 

attack by them. The application of fungicides will influence the leaf 

surface microflora populations and different varieties will also have 

different populations of leaf surface organisms.

44 


Physiological leaf spots in response to 

disease attack 

For several years, plant breeders have used effective resistance genes 

known as mlo genes to breed varieties with resistance to powdery 

mildew. Some of these varieties will induce a hypersensitive reaction 

when powdery mildew spores attack the plant leading to distinct leaf 

spots commonly known as target spots. 

Distinctive leaf spots associated with mildew infection on mildew resistant varieties

Leaf spots associated with powdery mildew infection on some barley varieties 


Powdery mildew is generally absent from these lesions, but irregular 

brown spots can develop around powdery mildew lesions on 

susceptible varieties. Fungal growth is usually associated with these 

lesions, but in some cases it can be absent where the mildew fungus 

has died off.

46 

Control of physiological leaf spot 

Keeping crops free from stress is the key to minimising the impact of 

physiological leaf spots. Some things can be done to minimise stress 

including variety choice, nutrition and also choice of fungicides 

Stresses from extreme weather events including frost, waterlogging, 

drought or prolonged sunshine are more challenging to manage. 

Variety 

Since some varieties are more susceptible to producing physiological 

leaf spots than others, varietal choice is one method to minimise their 

impact. In recent years, plant breeders have made advances in 

breeding varieties which are less susceptible to producing leaf spots. 

Nutrition 


Crops should be adequately provided with nutrition from macro 

nutrients including nitrogen, potassium and phosphorus and 

micronutrients in particular manganese which can cause stress when 

plants are deficient. 

Nitrogen is most likely to be limiting in varieties grown for malting 

markets which require grain with a low nitrogen level (1.4%). 

Growers should therefore be aware that crops grown for these 

markets are at a greater risk from physiological leaf spots. 

Manganese deficiency is a common nutritional disorder in barley 

grown on soils with a pH greater than 6.0. Deficiency symptoms 

include the development of brown linear flecks on leaves which can be 

indistinguishable from some physiological leaf spots. Since manganese 

is an important component of many plant enzymes, deficient plants 

are likely to be more susceptible to the development of physiological 

leaf spots as the plants ability to produce superoxide dismutase 

enzymes will be reduced. Protection against manganese deficiency is 

through the use of seed and foliar manganese treatments. Soil 

applications are unlikely to be effective since soil levels are likely to be 

high, but the availability of soil manganese is limited at high soil pH.

Manganese deficiency symptoms on barley 


Magnesium deficiency is more likely to occur in acid soils since soil 

magnesium is less available to the crop at low soil pH. Leaves of 

plants affected by magnesium deficiency are likely to show necrotic 

leaf spots on the leaf margins. The underlying soil pH can be corrected 

using magnesian limestone. Where a foliar treatment is required, 

magnesium sulphate can be applied.

48 


Magnesium deficiency symptoms on barley

Activity of fungicides against physiological leaf spots 

Strobilurins 

FOLIAR FUNGICIDE TREATMENTS 49 

Some strobilurins can reduce the effect of physiological leaf spots. 

Research has shown that pyraclostrobin improves the ability of the 

crop to tolerate stress. This activity is due to its direct effect on 

levels of the enzyme superoxide dismutase which breaks down 

damaging compounds in the leaf produced in response to stress, 

including high light intensity. Increased levels of superoxide 

dismutase activity have been measured following treatment with 

pyraclostrobin, which then gives the plant a level of protection 

against stress within the plant. 

Other fungicides can produce similar effects, but it is unknown if this 

is due to a direct effect from the fungicide or in response to antioxidant 

components in the formulated products. 

Ramularia Physiological 

leaf spot leaf spot 

azoxystrobin 

picoxystrobin 

- 

- 

** 

- 

pyraclostrobin 

trifloxystrobin 

Triazoles 

- 

- 

*** 

- 

epoxiconazole ** ** 

prothioconazole 

Other straight ais 

*** **** 

chlorothalonil *** **** 

cyprodinil 

Mixtures 

* ** 

azoxystrobin + chlorothalonil *** **** 

epoxiconazole + boscalid *** **** 

isopyrazam + cyprodinil *** **** 

prothioconazole + fluoxastrobin *** **** 

**** 

*** 

** 

* 

Excellent protection 

Good protection 

Moderate protection 

Low protection 

- No protection

50 

FUNGAL DISEASES CAUSING SYMPTOMS SIMILAR TO RAMULARIA LEAF SPOTS 

Fungal diseases causing symptoms similar to 

ramularia leaf spots 

Net blotch (Pyrenophora teres) and spot form of net blotch (Pyrenophora teres f 

maculata) 

Net blotch is a common disease of barley whose symptoms can be easily 

mistaken for ramularia leaf spot. Net blotch produces dark brown 

lesions on a leaf which can be associated with leaf yellowing. In its most 

typical form, the lesions have a netted appearance. And lesions are not 

contained by the leaf ridges. 

The spot form of net blotch produces smaller lesions that are very similar 

to ramularia leaf spot. Ramularia leaf spot lesions tend to be more 

rectangular with straight longitudinal sides to the lesion than the spot 

form of net blotch. Net blotch symptoms are typically longer and more 

irregular than ramularia leaf spot. It is possible for the two diseases to be 

present on the same leaf in which case a more detailed microscopical 

analysis would be required to differentiate the two diseases. 

Net blotch symptoms on barley

FUNGAL DISEASES CAUSING SYMPTOMS SIMILAR TO RAMULARIA LEAF SPOTS 51 

Spot form of net blotch lesions on barley

52 


Pyrenophora leaf stripe (Pyrenophora graminea) 

Pyrenophora leaf stripe is a seed-borne disease which produces 

longitudinal yellow and brown stripes on a leaf. Since the disease is seed 

borne, the stripes will originate from the base of the leaf. These 

symptoms are more likely to be mistaken for physiological leaf spots 

which can occur in stripes on some varieties. 

Pyrenophora leaf stripe on barley

FUNGAL DISEASES CAUSING SYMPTOMS SIMILAR TO RAMULARIA LEAF SPOTS 53 

Halo spot (Selenophoma donacis) 

Halo spot is a leaf spotting disease of barley which produces small 

irregular pale lesions on a leaf with a defined dark brown margin. This 

disease is generally uncommon but can develop on the upper leaves in a 

wet season when it can be confused with ramularia leaf spot or 

rhynchosporium secalis 

Halo spot caused by Selenophoma donacis on barley

54 

Septoria nodorum 


Septoria nodorum produces oval shaped brown lesions on a leaf 

surrounded by a yellow halo. The lesions are not confined by the leaf ridges 

unlike ramularia leaf spots. Septoria nodorum symptoms are more common 

on the lower leaves and develop up the leaf canopy. This is in contrast to 

ramularia leaf spot which is typically more common on the upper leaves. 

Septoria nodorum lesions on barley

Glossary 

GLOSSARY 55 

Abiotic leaf spots – leaf spots caused by physical stress 

including light, weather and chemical 

Asymptomatic – causal fungus present in plants but not 

expressing symptoms of ramularia leaf 

spot 

Endophyte – fungus or bacteria living inside the plant 

without causing any visible symptoms 

Mlo - mildew resistance genes in barley 

Pathogen – an organism that causes disease 

Polycyclic epidemic – a disease which once established will 

spread further if weather conditions are 

suitable 

Physiological leaf spots – leaf spots caused by physical stress 

including light, weather and chemical 

Ramularia collo-cygni – causal fungus of Ramularia leaf spot 

Ramularia leaf spot – common name for the disease caused by 

Ramularia collo-cygni 

Stomata – pores on the leaf

56 

REFERENCES AND FURTHER READING 

References and further reading 

Datnoff LE, Elmer WH, Huber DM, (2007) Mineral nutrition & plant 

disease 2007 edited (The American Phytopathological Society). 

Frei P, Gindro K, Richter H & Schürch S (2007) Direct-PCR detection 

and epidemiology of Ramularia collo-cygni associated with barley 

necrotic leaf spots. Journal of Phytopathology 155: 281-288. 

Havis ND, Oxley SJP, Piper SR & Langrell SRH (2006a) Rapid nested 

PCR-based detection of Ramularia collo-cygni direct from barley. 

FEMS Microbiology Letters 256: 217-223. 

Havis ND, Pastok M, Pyzalski S & Oxley SJP (2006) Investigating the 

life cycle of Ramularia collo-cygni. pp. Proceedings Crop Protection in 

Northern Britain, Dundee, UK, Feb 2006. 

Havis ND, Nyman M, Oxley SJP (2010) Potential of seed treatment to 

control Ramularia collo-cygni in barley. Proceedings of Crop Protection 

in Northern Britain -102. 

Heiser I, Sachs E, Liebermann B, (2003) Photodynamic oxygen activation 

by rubellin D, a phytotoxin produced by Ramularia collo-cygni (Sutton et 

Waller) Physiological and molecular plant pathology 62 29-36. 

HGCA Barley Disease Management Guide 2009. 

Huss H (2004) The biology of Ramularia collo-cygni. Meeting the 

Challenges of Barley Blights (Yahyaoui AH, Brader L, Tekauz A, 

Wallwork H, Steffenson B, eds), pp. 321-328. Proceedings of the Second 

International Workshop on Barley Leaf Blights, (ICARDA), Aleppo, 

Syria, April 2002. 

Koopman B, Oxley S, Schützendübel A, von Tiedemann A (2006) 

Ramularia collo-cygni: a new disease and challenge in barley; 

proceedings; First European Ramularia workshop web address: 

http://www.user.gwdg.de/~rcc/index.htm 

Makepeace JC, Oxley SJP, Havis ND, Hackett R, Burke JI, Brown JKM 

(2007) Associations between fungal and abiotic leaf spotting and the 

presence of mlo alleles in barley. Plant Pathology 56: 934-942.

REFERENCES AND FURTHER READING 57 

Makepeace JC, Havis ND, Burke JI, Oxley SJP, Brown JKM (2008) 

A method of inoculating barley seedlings with Ramularia collo-cygni. 

Plant Pathology 57 991-999. 

Oxley SJP, Havis ND, Sutherland KG & Nuttall M (2002). 

Development of a rationale to identify the causal agent of necrotic 

lesions in spring barley and to identify control mechanisms. HGCA 

Project Report No 282. HGCA publications, London, UK. 

Oxley SJP, Havis ND (2004). The development of Ramularia collocygni 

on spring barley and its impact on yield. The Dundee Conference 

Crop protection in Northern Britain p147-152. 

Oxley SJP, Burnet FJ (2009) Barley Disease Control Technical Note 

TN627 ISBN 185482874. 

Oxley SJP, Brown JKM, Foster V, Havis ND (2009) The 2nd European 

Ramularia Workshop (2008)- A new disease and challenge in barley 

production Aspects of Applied Biology 92. 

Oxley SJP, Havis ND, (2010) Managing Ramularia collo-cygni through 

varietal resistance, seed health and forecasting. HGCA Project report 

no 463. 

Sutton B & Waller J (1988) Ramularia collo-cygni. Transactions of the 

British Mycological society 90 57 (IMI description of fungi and 

bacteria no 1039). 

Walters DR, Havis ND, Oxley SJP, (2008) Ramularia-collo-cygni: the 

biology of an emerging pathogen of barley to FEMS Microbiological 

Letters 279 1-7. 

Yue-Xuan Wu, Andreas von Tiedmann (2004) Light dependent 

oxidative stress determines physiological leaf spot formation in barley. 

Phytopathology 94 p584-592. 

Yue-Xuan Wu, Andreas von Tiedmann (2002) Evidence for oxidative 

stress involved in physiological leaf spot formation in winter and spring 

barley. Phytopathology 92 p145-155. 

Outside Back Cover picture: shows artificially coloured image of 

Ramularia collo-cygni spore on distinctive curved conidiophore.

58 

ACKNOWLEDGEMENTS 

Acknowledgements 

Authors: Simon Oxley, Neil Havis and Andy Evans 

of SAC 

Editing and formatting: Steve Waterhouse and Lindy Tonguç of 

BASF 

Photographs: Simon Oxley, Neil Havis, Lawrence 

Morrice and Martin Richards. SAC 

Copyright. 

Research funding: HGCA and Scottish Government 

Publication funding: BASF plc and SAC 

® = Registered trademark of BASF 

Tracker contains boscalid + epoxiconazole. 

Always read the label. Use pesticides safely.

Disclaimer 

SAC, HGCA and BASF plc, Crop Protection have provided 

funding for this publication. While the authors have worked on 

the best information available to them, neither SAC, HGCA nor 

BASF plc shall in any event be liable for any loss, damage or 

injury howsoever suffered directly or indirectly in relation to 

this publication or the research on which it is based. 

Reproduction of material 

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