Prairie Crop Disease Monitoring Network (note the PCDMN Blog is no longer active): End-of-season assessment of cereal leaf spots in wheat and barley (PCDMN)

The spring and summer of 2023 was challenging for Prairie producers who experienced very dry conditions, especially under dryland production. Although this limited disease issues, the drought stress had a very significant negative impact on stand establishment, crop growth, and yield. However, some Prairie regions did receive moisture during the course of the summer and in these regions field crop diseases may be more of a concern.

Although the period for scouting, risk assessment, and fungicide use is drawing to a close for cereal leaf spots in 2023, 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:

Tan spot caused by the fungus Pyrenophora tritici-repentis;
Speckled leaf blotch aka septoria tritici blotch caused by the fungus Zymoseptoria tritici aka Septoria tritici aka Mycosphaerella graminicola;
Parastagonospora leaf and glume aka septoria nodorum leaf and glume blotch caused by the fungus Parastagonospora nodorum aka Stagonospora/Septoria nodorum;
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

Speckled leaf blotch

Glume blotch. Photo courtesy of Dr. Jeannie Gilbert

Glume blotch

Leaf/glume blotch

In barley, the main leaf spots include:

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;
Net-form net blotch caused by the fungus Pyrenophora teres f. teres;
Spot-form net blotch caused by the fungus Pyrenophora teres f. maculans;
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

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 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 wheat leaf to assess percent tan spot or septoria complex

• Standard area diagrams of barley leaf to assess net-form net blotch

• Standard area diagrams of barley leaf to assess spot-form net blotch or spot 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.