by Dr. Charla Hollingsworth, U of MN Extension Plant Pathologist
Bacterial leaf stripe is a disease that can usually be found on wheat in the Red River Valley (RRV) later as crop growth stages progress. The disease (caused by a Xanthomonas sp.) can develop and become severe rapidly after the crop reaches the heading growth stage. Bacterial leaf stripe (BLS) can cause significant yield losses on some varieties. Like other disease issues, development is dependent on weather conditions and the presence of susceptible plant hosts. Epidemics of BLS occurred in the RRV during 2005 and again in 2008.
Bacterial leaf stripe symptoms appear after the crop has reached the heading growth stage. Plant leaves show longitudinal striping, and/or blotchy yellow or brown lesions (Figure 1 and Figure 2). During periods with leaf wetness, lesions and plant tissues surrounding them, appear water-soaked and feel slimy if touched. When plant tissues 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 a donut. In this case, however, the glazing consists of millions of dry bacterial cells that are awaiting transport to another leaf or plant.
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.
Application of fungicides is not recommended. While fungicides are often applied to control diseases caused by fungi (e.g.: Fusarium head blight, 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.