Foliar Diseases of Wheat

Figure 1. Speckled (Septoria) leaf blotch
  • Foliar diseases may reduce yields or grain quality if they build to significant levels
  • Key diseases to monitor include stripe rust, leaf blotch complex, and powdery mildew
  • A timely and informed fungicide application targeting the flag leaf and head can minimize yield losses in high-risk situations 

Wheat growth is underway and over the next month we will start to see plants moving into critical periods of growth where canopies  close and flag leaves start to emerge.  The flag leaf and leaf immediately below the flag leaf contribute the lions share of carbohydrates needed for grain fill, and therefore keeping these tissues free of damage during grain fill is key in maximizing yields.  There are several foliar diseases that damage wheat.  This article will discuss the more common diseases, scouting recommendations, and treatment options.   

 

Septoria (Speckled) Leaf Blotch
This is a residue-borne fungal disease that is favored by cool, wet conditions.  It occurs frequently in most regions where wheat is grown.  However, it typically does not move into the upper canopy due to its temperature and moisture requirements.  Losses due to speckled leaf blotch minimal in most scenarios.  The disease often occurs first in the lower canopy after jointing (Feekes 6) and will be evident as canopies grow and approach flag leaf emergence (FGS 8).  Look for brown irregular lesions, often with yellow margins.  Within the lesions dark black pinhead sized “balls” are often easily observed.   

 

Powdery Mildew
Powdery mildew is favored by cool temperatures and humid, but not wet conditions.  In fact, spore germination is inhibited by water on foliage.  This season the cool humid conditions likely have flared up this disease in some areas where susceptible wheat is planted. In recent years population shifts in the pathogen that have resulted in it being able to overcome some commonly deployed powdery mildew resistance genes in wheat, resulting in flareups in some areas.  
 

The disease typically occurs in focal points within a field, often in areas that favor cooler temperatures and greater humidity.  These areas include along fence lines, low lying areas of the field, or shaded forest edges.  Signs of the pathogen are observed as white fuzz on foliage that will turn grey and potentially contain black fungal growths on these grey or white masses over time.  This disease is often more problematic in situations where we are really pushing our N rates early or using manure in our production systems.