Field Crop Diseases
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Bacterial Wilt

 



Symptoms:
  • Severely infected plants will appear yellow-green, stunted, and have spindly stems and small, deformed leaflets.
  • In early stages of disease development, plants are often scattered throughout a field and symptoms include mild cupping, curling and mottling of leaves.
  • Infected plants are often most easily noticed in re-growth after the first cut.
  • Cross sections of the upper portion of infected roots have a yellowish-brown discoloration in the vascular system, and the discoloration may spread across the entire root as disease severity increases.

Pathogen Involved:
  • Clavibacter michiganense subsp.insidiosum (a bacterial pathogen)
  • This pathogen survives in plant residue in the soil.
  • The bacteria infect plants through wounds in the roots and crown or through the cut ends of newly mowed stems.
  • Can can survive and be spread in contaminated seed.

Time of Occurrence:
  • Plants are very susceptible during harvest.
  • Disease increases as alfalfa stands age, and disease typically first seen in the second or third year of a stand.

Conditions Favoring Disease:
  • Plants wounded by physical damage.
  • Disease incidence and severity is increased by the interaction of the bacterial wilt pathogen and the northern root-knot nematode and the stem nematode.

Disease Management:
  • Choose and plant highly resistant alfalfa cultivars.
  • Rotate fields out of alfalfa for three or more years.
  • Avoid mowing plants when leaves and stems are wet.
  • Young stands should be harvested before older stands if the same harvesting equipment is used.

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