Verticillium Wilt
Symptoms:
- Infected plants become yellowed and stunted, and leaves may fall off the lower portion of the infected stem.
- In the early stages of disease, the yellowing often first appears as a V-shaped area at the leaf tip, and leaflets may roll upward along their length. As the disease progresses, the leaves may become bleached, white to pink in color and die.
- Affected plants usually are scattered in a field.
- Stems usually remain green while leaves die and frequently remain attached to the stem.
- Leaf-to-leaf distance (node length) is shorter on infected than on healthy stems.
- There are no external root symptoms, but an orange-brown ring may develop inside the root in the vascular system.
- Plants are killed over a period of months
Pathogen Involved:
- Verticillium albo-atrum (a fungus)
- This pathogen can be seedborne
Time of Occurrence:
- All season
- Severity and incidence tends to increase after the first year of harvest
Conditions Favoring Disease:
- Verticillium wilt is rarely found in first-year stands, and the severe symptoms often occur in the second or third stand year.
- Infection can occur in stems or roots.
- Verticillium spores are produced on cut stubble, and are spread by harvesting equipment and foraging animals. Spores can also be spread by contaminated seed.
Disease Management:
- Planting alfalfa cultivars with resistance to Verticillium wilt is the most effective way to control this disease. Plant clean, certified seed.
- Rotate to another crop for 2-3 years, and control weeds, even during periods of non-alfalfa rotations, because some weeds are hosts for Verticillium and can sustain the pathogen.
- Harvest young fields before old fields, and clean equipment between fields.