Effective Friday, September 17, a province-wide mandatory masking order will be implemented for all indoor public spaces. 

Google Translate Disclaimer

A number of pages on the Government of Saskatchewan's website have been professionally translated in French. These translations are identified by a yellow box in the right or left rail that resembles the link below. The home page for French-language content on this site can be found at:

Renseignements en Français

Where an official translation is not available, Google™ Translate can be used. Google™ Translate is a free online language translation service that can translate text and web pages into different languages. Translations are made available to increase access to Government of Saskatchewan content for populations whose first language is not English.

Software-based translations do not approach the fluency of a native speaker or possess the skill of a professional translator. The translation should not be considered exact, and may include incorrect or offensive language. The Government of Saskatchewan does not warrant the accuracy, reliability or timeliness of any information translated by this system. Some files or items cannot be translated, including graphs, photos and other file formats such as portable document formats (PDFs).

Any person or entities that rely on information obtained from the system does so at his or her own risk. Government of Saskatchewan is not responsible for any damage or issues that may possibly result from using translated website content. If you have any questions about Google™ Translate, please visit: Google™ Translate FAQs.

Tan Spot

By Sherri Roberts, PAg, Crops Extension Specialist, Weyburn

July 2021

Typical symptoms of tan spot on wheat
Typical symptoms of tan
spot on wheat.

Tan spot or yellow leaf spot is caused by the fungal pathogen Pyrenophora tritica-repentis. This disease affects both spring and winter wheat, durum and certain native grasses. Currently, eight different races have been identified in the prairies and they are all host specific. Symptoms start out as small, dark brown to black spots that will first appear on the lower leaves of the infected plant. These spots expand out and develop longitudinally along the veins.

To distinguish these lesions from similar ones created by stagonospora/septoria leaf blotch, examine the lesions with a hand lens. Tan spot lesions will not have pycnidia (small, black fruiting bodies) present.

This fungus overwinters on crop residue. Due to prairie winter conditions, the reproductive organisms that allow this disease to overwinter are delayed in developing. The pseudothecia (sexual fruiting bodies) form on the residue. As a result, rotations that contain wheat back to back are extremely vulnerable to this disease. Studies done in Saskatchewan have that shown two-year-old wheat stubble is an even greater source of infected residue. The spores that spread this disease are produced in the spring and are carried on the wind or rain to young plants. Symptoms will appear five-seven days after infection.

Tan spot lesions forming irregular blotches on a leaf
If moisture and temperature
conditions are favorable, lesions
will coalesce together and form
irregular blotches.

During the growing season, conidia (asexually produced spores) are produced in old lesions on wet leaves. These conidia will become air borne as the infected leaves dry. At least six hours of leaf wetness is required before these conidia can infect and colonize new leaf tissues. Temperatures below 20 C will slow development as well as temperatures above 28 C. Hot temperatures in the summer generally prevent spread of this disease to the upper leaves.

The most effective method of controlling tan spot is sound crop rotation. There should be at least a three year spread between wheat crops. Fungicide applications need to be accessed as to the economic benefits. Generally, this disease affects the lower leaves early in the season and then as previously stated, summer temperatures and drier weather keep the disease from spreading to the flag leaf. If weather conditions are instead cool and wet during formation of the flag leaf, a fungicide application may be warranted to prevent the disease from destroying photosynthetic leaf area and infecting the seed. If seed heads are infected, grade reduction may occur due to lighter kernel weight and shriveled, off coloured seeds.

We need your feedback to improve saskatchewan.ca. Help us improve