Bacterial Leaf Spot of Alfalfa
Bacterial leaf spot is caused by Xanthomonas alfalfae subsp. alfalfae. It has been found in several midwestern U.S. states, as well as in Florida and Maryland. It is generally of minor importance but may be severe in particular locations. Lesions on leaves and stems initially are small spots appearing water-soaked. Lesions increase in size and merge with favorable weather conditions. The tan to yellow leaf lesions have dark borders and appear dry. Yellow halos may be observed around lesions. If symptoms are severe, leaves become “papery” as tissue death occurs, beginning at the leaf apex. Stem lesions elongate, becoming dark-margined with light green centers; bacterial exudate may form on lesions. Other symptoms include stunting, lodging, and plant defoliation. Seedlings infected in the fall can show symptoms of damping off due to the disease.
Bacterial leaf spot causes lesions on alfalfa leaves and stems.
Deborah Samac
Bacterial leaf spot symptoms on young alfalfa plants.
Deborah Samac
Bacterial leaf spot development is favored by rainy and hot conditions. X. alfalfae survives in plant residue and soil. It infects the plant when infested soil is splashed or blown onto plant tissue.
Management includes spring planting and avoiding infection through windbreak establishment and wind erosion mitigation.
Prepared by the Alfalfa Pest Management Working Group.
Leaf and stem lesions symptomatic of bacterial leaf spot. Deborah Samac.
Bacterial leaf spot symptoms on young alfalfa plants. Deborah Samac.
Alfalfa plants with bacterial leaf spot. Deborah Samac.
Alfalfa plants with papery leaves, a symptom of bacterial leaf spot. Deborah Samac.
Bacterial leaf spot stem lesion. Deborah Samac.
Gallery images courtesy Deborah Samac.
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