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.