Bacterial leaf streak and black chaffe of wheat

Over the past few weeks I’ve received numerous calls regarding wheat leaves and heads that have gone from not presenting disease-like symptoms to presenting disease symptoms in a short period of time.  In addition to leaf symptoms (see top photo), in some cases, heads or small portions of the glumes have developed a purplish discoloration (see bottom photo with purplish areas on the head).  In isolated and specific situations a fungicide was applied and symptoms have still presented themselves.  In fact, within a week, the variety trial in Stoneville went from flag leaves appearing green with no disease-like symptoms, to having brown streaks covering the majority of the leaf from top to bottom with no symptoms on leaves below the flag leaf.  The brown lesions associated with bacterial leaf streak can oftentimes appear on awns, leaves, glumes (head), and on the stem itself.  Symptoms typically appear after heading and more often than not are confused with those of Septoria leaf and glume blotch.  However, the greatest difference between the two has to do with the short period of time required for the bacterial diseases to develop and when lesions associated with Septoria leaf blotch are fully mature fungal fruiting structures that will appear as black pepper grains within the lesion will develop.  Also, upon close inspection the lesions caused by the bacterial pathogen will appear to be contained between the veins of the leaf rather than crossing the veins.  Lesions will begin as water-soaked spots with this particular phase disappearing within one day.  Moreover, lesions can and oftentimes only appear on the flag leaf.  Typically, Septoria leaf blotch will start from the bottom of the plant and move up while the bacterial disease will begin at the top of the plant.

Even though in some situations the disease appears to be severe publications suggest that the disease will not result in a yield reduction.  Moreover, a fungicide would not have remedied the problem since bacteria are involved in the disease.