End-of-season assessment of cereal leaf spots in wheat and barley (PCDMN)

 Although the period for scouting, risk assessment, and fungicide use has drawn to a close for cereal leaf spots in 2022,  producers and consultants may want to look at end-of season assessments. Late season crop scouting is critical for assessing the prevalence, severity and impact of these disease issues. Moreover, where unsprayed check strips or areas have been left in the field, late season assessments can be used to assess the impact and benefit of spraying in relation to leaf spot management and crop productivity.

The Prairie Crop Disease Monitoring Network (PCDMN) has developed recommended protocols for assessment of cereal leaf spots and estimates of potential yield loss.  In addition, the PCDMN has developed information on the identification of cereal leaf spot diseases.  

The main leaf spot
diseases in wheat include:
 

  1. Tan spot caused by the
    fungus Pyrenophora tritici-repentis
  2. Speckled leaf blotch aka
    septoria tritici blotch caused by the fungus Zymoseptoria tritici aka Septoria
    tritici
    aka Mycosphaerella
    graminicola
  3. Parastagonospora leaf and
    glume aka septoria nodorum leaf and glume blotch caused by the fungus Parastagonospora nodorum aka Stagonospora/Septoria nodorum
  4. Spot blotch caused by the
    fungus Bipolaris sorokiniana aka
    Cochliobolus sativus.  It can be found in the Prairie region,
    but it tends to be more of a minor issue for wheat crops.  

Tan spot


Tan spot


Tan spot


Speckled leaf blotch


Speckled leaf blotch


Glume blotch.  Photo courtesy of Dr. Jeannie Gilbert


Glume blotch.  Photo courtesy of Dr. Jeannie Gilbert


Glume blotch


Glume blotch


Leaf/glume blotch



In barley, the main
leaf spots include:
 

  1. Scald caused by the fungus
    Rhynchosporium secalis aka Rhynchosporium commune.  Scald tends to be more of a cooler
    region disease affecting barley mainly in the cooler moister regions of Alberta;
  2. Net-form net blotch caused
    by the fungus Pyrenophora teres
    f. teres
  3. Spot-form net blotch
    caused by the fungus Pyrenophora
    teres
    f. maculans
  4. Spot blotch caused by the
    fungus Bipolaris sorokiniana aka
    Cochliobolus sativus.
Early symptoms of scald


Mature symptoms of scald


Early symptoms of net-form net blotch


Progressing symptoms of net-form net blotch

Mature symptoms of net-form net blotch


Early symptoms of spot-form net blotch


Mature symptoms of spot-form net blotch

Spot blotch


Spot blotch


One complicating factor with cereal leaf spots is potential confusion with symptoms of bacterial leaf streak in both wheat and barley.  The PCDMN also has some information on BLS that can be used to differentiate this disease from the fungal leaf spot complex in cereals.


Bacterial leaf streak of barley.  Note bacterial ooze, greasy appearance of leaf


Bacterial leaf streak of barley.  Note bacterial ooze, greasy appearance of leaf


Bacterial leaf streak of barley.  Note dried bacterial ooze (glazed doughnut appearance), greasy appearance of leaf

Bacterial leaf streak of barley.  Note dried bacterial ooze (glazed doughnut appearance), greasy appearance of leaf


Bacterial leaf streak of barley.  Note dried bacterial ooze (glazed doughnut appearance), greasy appearance of leaf



Access the Cereal Leaf Spot Assessment Protocols as a downloadable PDF file. 



Access diagrammatic images of different levels of cereal leaf spots using these  hyperlinks: 
• Standard area diagrams of wheat leaf to assess percent stripe rust
• Standard area diagrams of barley leaf to assess net-form net blotch
• Standard area diagrams of barley leaf to help assess scald

The use of standard area diagrams can help in terms of determining the level of leaf spot development.  Here are some standard area diagrams showing 1, 5, 10, 25, and 50% of the leaf area affected with various leaf spot diseases in barley and wheat.  Note that symptoms of spot-form net blotch and spot blotch in barley can be difficult to distinguish without laboratory testing of plant samples.  In addition, differentiating tan spot from the septoria complex in wheat can be challenging even for experienced plant pathologists, and thus a lab diagnosis may be needed.  However, all cereal leaf spot diseases result in destruction of leaf tissues and thus affect grain yield and filling.  The goal should be correct identification of leaf spot disease issues and then assessment of the overall level, i.e. severity. 





Use the following list of hyperlinks to gain access to PCDMN resources for
cereal leaf spot identification:

Wheat:

·      Speckled leaf blotch

·      
Parastagonospora/Septoria leaf and
glume blotch

·      
Tan spot

·      
Fusarium head blight

·      
Fusarium head blight seed
infections

·      
Bacterial leaf streak

·      
Cereal rusts


Barley:

·      
Net-form net blotch in barley

·      
Spot-form net blotch in barley

·      
Scald in barley

·      
Spot blotch in barley

·      
Fusarium head blight

·      
Fusarium head blight seed
infections

·      
Cereal rusts