Anne Kirk, Manitoba Agriculture
Morgan Cott, Manitoba Crop Alliance
Simon Huang, Manitoba Agriculture

A corn disease survey was conducted across Manitoba in September of 2025.  Crop disease surveys are important for documenting the severity and geographical distribution of various diseases. Results from disease surveys provide warning about new diseases and help to prioritize where future research is needed. 

Methods

A total of 54 fields were surveyed across Manitoba to document the prevalence (% of fields having infection) and incidence (average % of plants showing infection within infected fields) of various corn diseases. Field were surveyed in September around the beginning of crop maturity.  

Plants were visually assessed for the presence of Goss’s wilt (Clavibacter michiganensis subsp. nebraskensis), common rust (Puccinia sorghi), common smut (Ustilago maydis), head smut (Sphacelotheca reiliana), and stalk rot.  Holcus spot (Pseudomonas syringae pv. syringae) was recorded in some but not all fields.  In each field, 50 plants were surveyed in a “W” pattern, where the five points of the “W” were at least 50 paces apart and 100 m from field edges.  The presence or absence of disease was noted for each of the 50 sampled plants per field, except for Goss’s wilt and holcus spot.  Goss’s wilt and holcus spot were simply recorded as present or absent for each field.

Results
At crop maturity Goss’s wilt was found in 54% of the fields sampled, making it the most common disease found in the fall survey.  Holcus spot was found in the majority of fields surveyed in the central region, but prevalence is not reported as all surveyors were not assessing plants for holcus spot. Head smut, common rust, stalk rot, and common smut were found in 33%, 11%, 7% and 6% of fields surveyed, respectively (Table 1). 

 Table 1. Results of the 2025 corn disease survey.  Prevalence (% of fields having infection) and incidence (average % of plant showing infection within infected fields) for each region and for all fields surveyed.

Acknowledgements
This survey was supported by Manitoba Agriculture and Manitoba Crop Alliance.  Thank you to the grower co-operators who allowed for their fields to be surveyed and provided surveyors with field information. 

Contributed by Anne Kirk, Cereal Crop Specialist with Manitoba Agriculture.