Bacterial Wilt of Alfalfa
Bacterial wilt is caused by Clavibacter insidiosus, and is a phytosanitary risk for international export of alfalfa seed. Disease is first observed when stands are 2 to 3 years old on scattered plants or in patches of plants within a field. Plants are stunted or dwarfed with yellowish and mottled foliage. Leaflets may show cupping or upward curling. Severe infection causes plants to appear “bunchy” with small leaves and yellowish tissue; plant death can occur. Regrowth following cutting may have the most obvious symptoms. Taproots will show internal yellow to tan discoloration.
Bacterial wilt foliar symptoms on alfalfa (plant on right).
Deborah Samac
Bacterial wilt root symptoms on alfalfa.
Deborah Samac
The pathogen survives on plant residue in the soil or in dry plant tissue for many years. The bacteria enters the plant through injury to stems, crowns, and roots and is slow to develop. Nematode infection can increase disease risk.
The best way to manage bacterial wilt is to plant resistant alfalfa cultivars. Practice harvest-equipment sanitation and limit movement of infested hay to mitigate field to field pathogen spread. Mow non-infected younger or Clavibacter-resistant stands first. Cut stands during dry conditions and manage irrigation to limit water ponding. Rotate away from alfalfa for two years if susceptible varieties are grown, ensuring volunteer alfalfa is eliminated and old crowns are destroyed through tillage.
Prepared and reviewed by the Alfalfa Pest Management Working Group.
Bacterial wilt foliar symptoms on alfalfa (plant on right).
Bacterial wilt root symptoms on alfalfa.
Bacterial wilt foliar symptoms on alfalfa.
Bacterial wilt root symptoms on alfalfa.
Gallery images courtesy Deborah Samac and Craig Grau.
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