Bacterial stripe, also termed black chaff, is a disease that can be found on wheat throughout the Red River Valley this year. The disease (caused by Xanthomonas campestris pv. translucens), appears to be universally more severe in fields of Granite hard red spring wheat. The disease can cause significant yield losses if it becomes severe early enough. Like other disease issues, development of bacterial stripe is dependent on weather conditions and the presence of susceptible plant hosts. Epidemics have been recorded only sporadically since the early 1900s.

Symptoms Bacterial stripe symptoms generally appear during the heading growth stage (Feekes 10.5 and later), and are known on glumes, as well as leaves. In the Red River Valley, plant leaves are showing stripes, and/or blotchy yellow or brown lesions (Figures 1 and 2). During periods with leaf wetness, lesions, and plant tissues surrounding them, appear water-soaked and feel slimy if touched. When plant leaves are dry and humidity is low, the same leaves will have a shiny appearance (Figure 3). Leaves look glazed as if they had been frosted with a thin sugary glazing, similar to the glazing on donuts. In this case, however, the glazing consists of millions of dry bacterial cells that are awaiting transport to another leaf or head.

If flag leaves are severely diseased early, yield losses may result. Maintaining the photosynthetic area of flag leaves is important in preserving yield and test weight potentials.

Spread
Bacteria are transferred from one leaf to another during periods of leaf wetness. Wind provides leaf movement which allows localized spread of bacteria from plant to plant. Because the pathogen is spread through contact with diseased plants, fields may have initial “hot spots” or patterns of diseased plants that run parallel with wind direction. Bacteria are also known to be spread by plant-visiting insects. Bacteria can survive in soil organic matter for an undetermined period of time and on (or within) seed.

Management
Application of fungicides is not recommended. While fungicides are often applied to control diseases caused by fungi (e.g.: scab, tan spot), they have no activity against bacteria. Identification of spring wheat varieties with bacterial stripe resistance is our best means of defense against loss. Currently, little is known on this topic.

Outlook for 2006
Disease development is largely dependent on the weather and varietal disease resistance. If environmental conditions don’t promote bacterial stripe development it won’t be a production issue in 2006.

Charla Hollingsworth
Extension Plant Pathologist