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 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. 

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

In case you missed it, the PCDMN posted some information on cereal leaf spot risk assessment and fungicide use decisions. 

2021 Cereal Rust Risk Report (May 12-20, 2021)

The latest Prairie wind trajectory cereal rust risk report is available for download now at the following link: May 12-20, 2021 report.  

As of May 20, 2021 the overall Prairie cereal rust risk assessment and need for in-crop scouting is as follows:

Pacific Northwest – Even though there were a number of reverse wind trajectories that passed over the PNW region and into the prairies, given limited stripe rust development in the PNW, generally dry Prairie weather conditions during the week of May 10-16, 2021, and early stages of Prairie crop development, as of May 20, 2021 the risk of stripe rust appearance from the PNW is limited and scouting for this disease is generally not urgent.

Texas-Oklahoma corridor – Given limited leaf and stripe rust development in this corridor (especially Texas), a smaller number of recent wind trajectories from this area, generally dry Prairie weather conditions, and early stages of Prairie crop development, as of May 20, 2021 the risk of leaf and stripe rust appearance from the Texas-Nebraska corridor is low and scouting for these diseases is not urgent. 

Kansas-Nebraska corridor – Stripe rust is continuing to develop in Kansas, and is progressing in Nebraska, while there were limited to no recent wind trajectories from this area into the central to western Prairie region.  However, there have been a number of trajectories that have passed over the central to eastern Prairie region.  Overall Prairie weather conditions have been dry during the period of May 10-16, 2021, and generally dry in Saskatchewan and Manitoba from April 17-May 16, 2021.  Prairie spring wheat development is still early, while winter cereals continue to develop.  As of May 20, 2021 the risk of leaf and stripe rust appearance from the Kansas-Nebraska corridor is low for the central to western Prairie region and moderate (mainly for stripe rust) for the central to eastern Prairie region.  Scouting for these diseases in winter wheat fields is recommended over the next 1-2 weeks, especially those planted to stripe rust susceptible varieties. 

Recent reports of stripe rust in Minnesota and Illinois suggest more northerly development of this disease and as a consequence growers in the central to eastern Prairie region should be on the look out for stripe rust over the next couple of weeks, especially in fields planted to susceptible winter wheat varieties. 

Mid-week mini cereal rust risk update - May 19, 2021

There has been a significant increase in the number of wind trajectories, originating over a number of states in the USA, that have crossed the prairies (Fig. 1). These air currents may introduce cereal rust spores into to the Prairie region. ECCC trajectory models indicate that air trajectories, originating over the Pacific Northwest (Idaho, Oregon, Washington), have crossed Alberta, Saskatchewan and western Manitoba (Fig. 2). Trajectories originating over Texas and Oklahoma have passed over eastern Saskatchewan and Manitoba (Fig. 3). A third group of trajectories, originating across Kansas and Nebraska have also crossed eastern Saskatchewan and Manitoba (Fig. 4). Though these US regions can be a source of cereal rust spores, the ECCC models predict air movement, not actual occurrence of cereal rust spores.  However, stripe and leaf rust continue to develop in the Oklahoma to Nebraska corridor, while development of stripe rust has generally been more limited in the Pacific Northwest.  Dry conditions in some Prairie regions and early crop development, especially in relation to spring cereals, may limit the risk.  However, scouting of winter wheat fields over the next 1-2 weeks, especially those planted to stripe and leaf rust susceptible varieties, should be considered in Prairie regions where these trajectories have occurred. 

The full PCDMN weekly cereal rust risk report will be available later this week and will include an overview of the cereal rust situation in key source regions in the USA.  

The PCDMN thanks Ross Weiss and Meghan Vankosky, AAFC Saskatoon, Jennifer Otani, AAFC Beaverlodge, and the PPMN for passing along this recent wind trajectory information. 

Figure 1. Summary of the average number (5 day running average) of reverse trajectories that have crossed the Canadian prairies (May 1-19, 2021).

Figure 2.  The green region indicates potential introduction of stripe rust uredospores from the Pacific Northwest (Idaho, Oregon, and Washington) to the Canadian prairies (May 18-19, 2021).

Figure 3.  The green region indicates potential introduction of stripe and leaf rust uredospores from Texas and Oklahoma to the Canadian prairies (May 18-19, 2021).

Figure 4.  The green region indicates potential introduction of stripe and leaf rust uredospores from Kansas and Nebraska to the Canadian prairies (May 18-19, 2021).