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:
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
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:
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
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
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:
