Issue No. 13, Article 6/June 20, 2008
A Plethora of Wheat Diseases in the Final Stretch
A number of diseases on wheat foliage and heads are now apparent in many Illinois fields in the final stretch of the wheat season. Foliar diseases, which seemed to have a slow start, have now moved into many fields. Diseases on the wheat heads are also apparent in some areas.
Some of the annually observed leaf diseases are present, which include the fungal foliar diseases caused by the Septoria/Stagonospora fungi complex. Symptoms due to Septoria/Stagonospora include lens-shaped spots on the leaves, with ashen gray centers that may contain black dots. Leaf rust has also been observed in central and southern Illinois fields; moderate to severe leaf rust was observed at research trials in Dixon Springs, and moderate levels have been observed in Brownstown and Urbana. Leaves that are symptomatic for barley yellow dwarf virus (leaves purple to red in color) can also be found in some fields.
In some fields, a few curiosities have appeared that do not appear to be caused by the usual fungal pathogen suspects. Some varieties appear to be particularly susceptible to bacterial stripe (the foliar symptom of black chaff--see below). Bacterial stripe, caused by the bacteria Xanthomonas, causes nondistinct necrotic lesions on the leaves. These lesions may "glisten" when the sun is shining on them. I have observed bacterial stripe in a few wheat varieties in one of my fungicide research trials, where most of the fungal diseases were controlled with a fungicide, but the bacterial stripe was not controlled (as expected). Other symptoms observed in the state include leaves with small white to yellow speckles. At this point, no pathogens have been found to be associated with this speckling; thus it appears to be physiological.
Leaves affected by the Septoria/Stagonospora fungal pathogen complex.
Leaf rust on wheat.
Symptoms of barley yellow dwarf virus on wheat.
Symptoms of bacterial stripe on wheat leaves.
White to yellow flecks observed on wheat leaves that appear to be a physiological disorder.
Head diseases observed thus far include scab (Fusarium head blight), glume blotch, and black chaff. Scab has been observed in many wheat fields in southern and central Illinois, but mostly in incidences below 5%. Glume blotch and black chaff have also been observed and reported in the state. Glume blotch, caused by the fungus Stagonospora nodorum, and black chaff, caused by the bacteria Xanthomonas, both cause dark lesions on the glumes of the wheat head. Lesions caused by glume blotch may contain small black speckles, whereas lesions caused by black chaff will not. In addition, lesions caused by black chaff may "glisten" when the sun is shining on them.--Carl A. Bradley
Scab (Fusarium head blight) of wheat.
Glume blotch of wheat.
Black chaff of wheat.
Carl A. Bradley