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Alfalfa Bacterial Wilt: Kentucky Alfalfa IPM

Bacterial Wilt


Symptoms

Affected plants first appear stunted with slow regrowth after cutting. Leaves turn yellow at the margin first, with the change in color gradually advancing over the whole stem or plant.

The best diagnostic symptoms occur in the tap roots. Dig ( do not pull) suspicious plants and look for yellowish-tan discoloration of the root vascular tissue. Overall the internal root tissues are yellow compared to white in healthy tap roots.

Cause

This disease is caused by the bacterium Clavibacter michiganense subsp. insidiosum. It penetrate taproots through wounds, such as those created by the clover root curculio. This disease shows up most often in stands that are at least three years old; it is seldom seen in the seedling year. Affected plants are usually scattered, not clustered.

IPM Techniques

  • Examine fields every four weeks from April 1 to October 1. Examine any suspicious looking plants within 100 feet of monitoring site. Report severity of the disease according to the following rating scale:

    0 = no infected plants, good healthy stand

    1 = a few plants have suspicious symptoms, appearance of some stunted or missing plants in stand

    2 = from 2 to 10% of plants infected

    3 = more than 10% of the plants infected, with thinning of the stand evident

  • Resistant cultivars should be planted.

  • Do not mow when plants are wet.

References and Additional Information

  • IPM-1 Kentucky Alfalfa IPM Manual

  • PPA-10d Kentucky Plant Disease Management Guide for Forage Legumes, P. Vincelli, Extension Plant Pathology, University of Kentucky

  • ID-104 Managing Diseases of Alfalfa, P. Vincelli, Extension Plant Pathology, and G.D. Lacefield and J.C. Henning, Agronomy, University of Kentucky

  • Compendium of Alfalfa Diseases. 2nd ed. Stuteville, D.L. & D.C. Erwin, (eds.). 1990.

This site was created and is maintained by Pat Dillon, Department of Entomology, University of Kentucky, S-225 Agricultural Science Ctr North, Lexington, KY USA  40546-0091 (phone: 859/257-3571). Please send questions or suggestions to: pdillon@uky.edu