Bacterial Stem Blight of Alfalfa
Bacterial stem blight is caused by Pseudomonas syringae pv. syringae and is found throughout the United States. Occurrence is usually limited to first growth hay and is often attributed to frost as symptoms tend to develop after freezing temperatures in late spring. Symptoms include stunting; short, spindly, and brittle stems; and stem lesions. Water-soaked lesions begin where petioles attach to the stem and can extend across several internodes. Bacterial exudate causes lesions to appear shiny and lesions eventually darken. Leaflets can become water-soaked and yellowish along the midrib and at the base. Petioles and leaves on infected stems will dry out and die.
Bacterial stem blight foliar symptoms.
Deborah Samac
Bacterial stem blight foliar symptoms.
Deborah Samac
Cold, wet springs are optimal for disease development. Symptoms appear after freezing weather in late spring. P. syringae pv. syringae survives on crop residue in the soil.
If disease is severe, harvest the first cutting as soon as possible after frost risk has passed.
Prepared and reviewed by the Alfalfa Pest Management Working Group.
Bacterial stem blight foliar symptoms.
Bacterial stem blight foliar symptoms.
Images courtesy Deborah Samac.
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