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Durum Symptoms in Western ND (07/29/21)

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Growers and agronomists have reported discolored awns and glumes of durum heads in several fields in western ND. The symptoms resemble those of Stagonospora glume blotch (fungal disease) and black chaff (bacterial disease). However, we believe that these symptoms may be caused by an abiotic (non-living) disorder. This article will review some of the key characteristics and observations from these samples.

Bleached Awns

Some of the samples have bleaching occurring on the upper half of the awns (Figure 1). This can be a common symptom when hot weather occurs at the start of heading. The damage caused by the heat is often localized on the upper portion of the awns and does not spread down to the glumes. We have also observed this symptom in hard red spring wheat this year.

Black Awns and Blotches on Head

The most puzzling symptoms have been blackening of awns and glumes that resemble a disease. The discolorations have been reported to occur across an entire dryland field and appear to be more spotty in occurrence in irrigated fields. The discolorations have also been found on more than one variety. When looking at these samples, there a few things that suggest an abiotic disorder is the cause:

  1. First thing to consider is the weather. The hot and dry conditions throughout July have not been favorable for disease development and has stressed the durum crop. Warm and humid conditions are needed for Stagonospora glume blotch and black chaff to develop.
  2. Leaf lesions. Check the flag leaves to determine if Stagonospora nodorum blotch or bacterial leaf streak are present. When durum or hard red spring wheat have Stagonospora glume blotch or black chaff, the pathogen will also be found on the leaves of the plant. In the submitted samples, the leaf lesions do not resemble Stagonospora nodorum blotch or bacterial leaf streak (Figure 2).
  3. Symptom location. When looking through the samples, it appears the symptoms are found on the entire head or are restricted to only one side of the head (Figure 3). Given that most main stems have symptoms on the entire head and tiller heads only have partial symptom development, leads us to believe that the stressor occurred during the heading stages of durum development. One potential stressor could be hot temperatures causing a physiological response (ie: blackening of awns) on the durum.
  4. Disease incidence in the state. Recent NDSU IPM survey efforts have found little to no disease present on wheat in the state. This includes the foliar diseases of Stagonospora/Septoria (referred to as SSC complex in the IPM survey) and bacterial leaf streak.

If you suspect disease or want lab confirmation that symptoms are abiotic in nature, submit samples to the NDSU Plant Diagnostic Lab for evaluation. Detailed submission instructions can be found at their website: NDSU Plant Diagnostic Lab.  

 

Figure 1. Bleaching on the upper portion of durum awns.

 

Figure 2. Leaf lesions are variable in shape (angular and oval) and in color (white, brown and black). These do not resemble lesions of Stagonospora nododrum blotch or bacterial leaf streak and Figure 3. Symptoms on the glumes vary ranging from an entire head to only one side of the head.

 

Audrey Kalil

Plant Pathologist

 

Andrew Friskop

Extension Plant Pathology, Cereal Crops