Wednesday, April 3, 2024

Continuing development of stripe rust in the USA may foreshadow a risk for Prairie wheat growers in 2024

Previous PCDMN blog posts have highlighted potential emerging stripe rust issues in the USA; unfortunately this may mean stripe rust issues for Prairie wheat growers.  Stripe rust risk forecasts from Dr. Chen, USDA-ARS and Washington State University (WSU), indicated the risk of stripe rust for 2024 for the eastern PNW is severe and susceptible winter wheat varieties will potentially incur yield losses (https://www.wawg.org/stripe-rust-report-warmer-november-december-dont-bode-well-for-susceptible-varieties/; https://smallgrains.wsu.edu/first-stripe-rust-forecast-of-the-2024-season/; https://www.wawg.org/march-1-stripe-rust-forecast-calling-for-epidemic-levels-for-eastern-washington/).  In addition, Dr. Chen reported stripe rust symptoms, indicating overwintering of stripe rust on winter wheat in the Pacific Northwest (PNW).  On March 19, 2024, Dr. T. Murrary, WSU, referred to Dr. Chen's forecasts and emphasized a potential stripe rust issue for the PNW in 2024, while indicating that not since February 2011 have symptoms of stripe rust been observed this early (https://smallgrains.wsu.edu/stripe-rust-324/).  Overall, rust risk forecasts for the PNW and the early occurrence of symptoms suggest the PNW may be an important source of stripe rust inoculum for Prairie wheat growers in 2024.  


In addition to the occurrence of symptoms in the PNW, there have also been multiple early reports of stripe rust on winter wheat in Texas and Oklahoma in late February and continuing into late March ( (S. Baker, Stripe rust at Chillicothe, TX, CEREAL-RUST-SURVEY@LISTS.UMN.EDU, February 26, 2024; https://twitter.com/J_SBaker/status/1752818506674929882).  Most recently Dr. M. Aoun, Oklahoma State University (OSU) wheat pathology program, reported that stripe rust is developing in Jackson and Tillman Counties in SW Oklahoma (https://spotlight.okstate.edu/wheat-pathology/2024/04/02/wheat-disease-update-2-april-2024/; https://twitter.com/OSUwheatdisease/status/1775200213545959453; https://twitter.com/osuwit/status/1774638870660804917; https://twitter.com/OSUwheatdisease/status/1772315284025593930; https://twitter.com/OSUwheatdisease/status/1770869304529199247).  Interestingly, Dr. B. Carver, OSU wheat breeder, indicated that not since the "early 2000s" have there been such early observations of increased levels of stripe rust.  Dr. M. Aoun also observed stripe rust symptoms in research plots in Payne County, and suggested that forecast cooler wetter conditions could promote further stripe rust development in Oklahoma.  


Although no stripe rust in Kansas has been reported, Drs. K. A. Onofre and E. De Wolf, Kansas State University, recently indicated that observations from Texas starting in late January 2024 and favourable weather conditions suggest stripe rust may be an issue in 2024 (https://eupdate.agronomy.ksu.edu/article_new/outlook-for-stripe-rust-in-2024-kansas-wheat-crop-584-3).  They emphasized the value of monitoring winter wheat for stripe rust symptoms as further crop development occurs.  Further development of stripe rust in the Texas to Nebraska corridor over the next 1-2 months could pose a risk for Prairie wheat growers, especially in central to eastern regions.  


Stay tuned for our regular weekly PCDMN rust risk forecasts starting in mid-May (https://prairiecropdisease.blogspot.com/p/cereal-rust-risk-report.html), while further updates on the US rust situation will be posted on the PCDMN blog.  

Monday, March 4, 2024

2nd stripe rust forecast for the eastern Pacific Northwest - Dr. X. Chen, March 1, 2024 : An updated heads up for Prairie cereal producers for 2024

This is an update to a PCDMN post on January 9, 2024.  Updated information from the Pacific Northwest (PNW) of the US provides a further head's up regarding potential Prairie stripe rust risk in 2024.  In his March 1, 2024 update, Dr. X. Chen, with USDA-ARS and Washington State University, indicates the risk of stripe rust for 2024 for the eastern PNW is severe and susceptible winter wheat varieties will potentially incur yield losses in the 40-60% range if they are not sprayed with fungicide.  The projected yield loss for highly susceptible varieties has increased from 42% with the January 2024 update (https://www.wawg.org/stripe-rust-report-warmer-november-december-dont-bode-well-for-susceptible-varieties/https://smallgrains.wsu.edu/first-stripe-rust-forecast-of-the-2024-season/to 51% for the March 1, 2024 update (https://www.wawg.org/march-1-stripe-rust-forecast-calling-for-epidemic-levels-for-eastern-washington/).  Fortunately, varieties with moderate to high levels of resistance will mitigate stripe rust risk and the need for fungicide.  However, virulence shifts can occur so keep this in mind if you start to see more stripe rust than expected in any resistant varieties you are growing on the Prairies.  Dr. Chen also indicated in his March 1, 2024 update that stripe rust appears to have successfully survived the winter on infected winter wheat crops, with multiple reports of symptoms in recently checked rust monitoring nurseries and commercial fields.  Moreover, these 2024 observations in Washington State, especially east of the Cascade mountains, are earlier compared to 2011 to 2023.  Overall, the PNW may have levels of stripe rust in 2024 that could threaten Prairie winter and spring wheat crops.  

Unfortunately, Dr. Chen also indicated in his March 1, 2024 update that there have been multiple reports of stripe rust in Texas and other southcentral States and these early observations suggest that these areas of the US may experience severe stripe rust epidemics if conducive weather occurs.  Observations of stripe rust in Texas by Texas A&M staff were recently posted by S. Baker, Texas A&M AgriLife Research, based on observations by J. Baker and D. Hathcoat (S. Baker, Stripe rust at Chillicothe, TX, CEREAL-RUST-SURVEY@LISTS.UMN.EDU, February 26, 2024; https://twitter.com/J_SBaker/status/1752818506674929882)

Each year the PCDMN issues weekly cereal rust risk forecasts based on rust development in source locations in the USA.  The PNW is mainly a concern in terms of stripe rust, while the Texas to Nebraska corridor represents a risk for leaf rust, stripe rust and stem rust, while there may be concerns related to crown rust in oat.  In addition to accounting for rust development in the US, the PCDMN also looks at the number of wind trajectories that may carry rust spores from US source locations, and Prairie crop development and weather conditions. 

You can keep up-to-date with Prairie cereal rust risk via PCDMN cereal rust risk forecasts that are posted to this blog from mid-May to early July each year and can be found at https://prairiecropdisease.blogspot.com/p/cereal-rust-risk-report.html

Key management strategies for cereal rusts include host resistance, scouting and awareness of emerging rust issues, and timely fungicide application.  It is advised that Prairie producers check the stripe rust resistance rating of the winter and spring wheat varieties they are or will be growing.  Timely scouting and consideration of fungicide use are advised for the 2024 growing season, especially for varieties that are susceptible to moderately susceptible to stripe rust.

The PCDMN will follow up with further risk reports from Dr. Chen as we move towards the 2024 Prairie growing season.

Typical symptoms of stripe rust are as follows: 








Tuesday, January 9, 2024

Stripe rust forecast for the eastern Pacific Northwest - Dr. X. Chen: A heads up for Prairie cereal producers for 2024

We are still a few months away from the 2024 Prairie growing season.  However, information from the Pacific Northwest (PNW) of the US does give a head's up regarding potential Prairie stripe rust risk in 2024 (https://www.wawg.org/stripe-rust-report-warmer-november-december-dont-bode-well-for-susceptible-varieties/).  Dr. X. Chen with USDA-ARS and Washington State University issues stripe rust forecasts for the PNW region based on weather conditions in November and December.  Unfortunately, Dr. Chen's update for January 8, 2024 indicates the risk of stripe rust for 2024 for the eastern PNW is severe and susceptible winter wheat varieties will incur average yield losses of 42% if they are not sprayed with fungicide.  Fortunately, varieties with moderate to high levels of resistance will mitigate stripe rust risk and the need for fungicide.  However, virulence shifts can occur so keep this in mind if you start to see more stripe rust than expected in the resistant variety you are growing.  Overall, the PNW may have issues with stripe rust that could threaten Prairie winter and spring wheat crops.  

Each year the PCDMN issues weekly cereal rust risk forecasts based on rust development in source locations in the USA.  The PNW is mainly a concern in terms of stripe rust, while the Texas to Nebraska corridor represents a risk for leaf rust, stripe rust and stem rust, while there may be concerns related to crown rust in oat.  In addition to accounting for rust development in the US, the PCDMN also looks at the number of wind trajectories that may carry rust spores from US source locations, and Prairie crop development and weather conditions. 

You can keep up-to-date with Prairie cereal rust risk via PCDMN cereal rust risk forecasts that are posted to this blog from mid-May to early July each year and can be found at https://prairiecropdisease.blogspot.com/p/cereal-rust-risk-report.html

Key management strategies for cereal rusts include host resistance, scouting and awareness of emerging rust issues, and timely fungicide application.  

The PCDMN will follow up with further risk reports from Dr. Chen as we move towards the 2024 Prairie growing season.

Typical symptoms of stripe rust are as follows: 







Monday, July 31, 2023

End-of-season assessment of sclerotinia stem rot of canola (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.

We are at or fast approaching the time when you can rate sclerotinia stem rot in your canola. Ideally, plants should be rated within a week or so before the crop would normally be swathed (if it was being swathed of course). Once the crop starts to turn, rating becomes very difficult. 





Key characteristics of sclerotinia infections in canola include:

  • Infected tissue has a characteristic bleached white/whitish/tan gray appearance
  • Affected tissue when it dries is very brittle and shreds and shatters easily when you twist the stems
  • The pith portion of affected stems is typically not present
  • In heavily infected stems the pith tissue is destroyed leaving only the outer ring of stem tissue
  • Sclerotia (black resting bodies) or sclerotial initials (clumps of compacted white hyphae that turn black when mature) are typically produced in or on affected plant tissues 
  • External sclerotia typically develop when you have wet conditions following infection and as the crop progresses towards senescence.


























Symptoms not characteristic of sclerotinia: 
  • Infected tissue doesn’t have a bleached white/whitish grey or tan appearance 
  • Affected tissue is not brittle and doesn’t shred and shatter when you twist the stems between your hands 
  • The pith portion of stems is still intact
  • Sclerotia or sclerotial initials (dense clumps of white hyphae) are not produced in/on suspect symptoms
  • Yellowing of stems/branches may be due to other factors, such as root disease, nutrient, or weather stress, etc.









For sclerotinia one can look at the incidence of infection, and focus on the main stems and branches. Infections on the main stem and/or branches have the largest impact on yield. However, if incidence is low (<5%), the impact on yield is negligible.  




In most canola fields, plants will typically lean in a particular direction.  Use this to your advantage and work with the flow of plants.


When assessing stem rot levels, one should look at a representative sample of plants throughout the field. For example, a minimum of 4-6 sites should be looked at in a quarter section field; then at each site between 50-100 plants should be assessed.  





Half or full section fields will require more sites.  If the field is quite variable then separate assessments in specific areas may be needed, e.g. lodged versus non-lodged. 









Assessments can also be made in sprayed versus check areas to determine the usefulness and benefit of in-crop fungicide applications.  Unsprayed checks, even small areas, can be quite useful.



An alternative rating scale is one from Kutcher and Wolf (2006).  Although a bit more complicated, it covers infections on various parts of the plant.  Note symptoms in the upper canopy (pods, etc.) generally have less impact on yield.

 

Rules of thumb have been developed to assess the potential loss associated with stem rot infections.  In general the % yield loss is approximately 0.5 times the % of infected plants (main stem or main branch infections).  Thus, if you note 30% infected plants, the potential yield loss is approximately 15%.  

The PCDMN has also produced overviews for assessment of stem rot levels and identification of disease symptoms accessible with the following hyperlinks: 

• An assessment protocol for sclerotinia stem rot in canola 

• A slide deck overview of a guide to scouting and identification of sclerotinia stem rot in canola 

• Playing cards describing sclerotinia stem rot of canola symptoms

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: 

  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