Scouting card for bacterial leaf streak of wheat

Here is our latest edition to the Prairie Crop Disease Monitoring Network (PCDMN) suite of disease scouting cards.  Over the past 5-10 years there has been increasing observations of bacterial leaf streak (BLS) in wheat as well as bacterial issues in other cereal crops. Unfortunately in 2020 there were reports across the Prairie region, especially in Saskatchewan and Alberta, of bacterial issues in cereals, including wheat.  Observations reported by farmers, consultants, and pathologists suggest in some wheat fields BLS may have resulted in moderate yield losses.  

Unfortunately, management options for BLS are limited and involve two main strategies: 

1) Avoiding seed known or suspected to be infected with the BLS pathogen, as seed-borne inoculum is one of the main sources of this pathogen; 

2) Extending rotational intervals to at least two years between wheat crops to reduce the amount of infected residue, which can be another BLS source.  

It is critically important to correctly identify symptoms in the field using information outlined in the new BLS scouting card as well as other sources.  Symptoms may be confused with fungal leaf spots of wheat such as tan spot, the septoria complex and stripe rust.  If typical symptoms are observed one may be able to differentiate BLS from tan spot, the septoria complex, and stripe rust.  However, if symptoms are not distinct then a laboratory diagnosis will be needed.  Access these links for scouting cards and symptoms:

• Bacterial leaf streak
• Tan spot
• Speckled leaf blotch
• Leaf and glume blotch
• Cereal rust symptoms (PCDMN scouting cards in development)

One other observation that can help to identify a potential BLS issue, is that farmers may experience a lack of symptom control when applying one or more fungicide applications during the growing season.  Although this may indicate potential issues with fungicide resistance, especially for speckled leaf blotch, it can also suggest that the observed symptoms may not be due to the fungal pathogens that cause cereal leaf spot complex or leaf/stripe rust.  Our current suite of fungicide-based seed treatments and in-crop foliar fungicides will not control BLS.

Conditions that favour development of BLS include: 1) irrigation; and 2) Severe weather events that result in torrential rain, hail, very strong winds, thundershowers and soil particle erosion.  These severe weather events may lead to plant tissue damage, which provides an avenue of entry to the BLS pathogen along with natural plant openings such as stomata. The BLS bacterial pathogen is spread by plant-to-plant contact, insects, and rain splashing or wind-driven rain.