Verticillium wilt (Verticillium dahliae and V. alboatrum)

Verticillium-infected tomatoes, potatoes, and melons wilt, become stunted and low-yielding, but do not usually die. Leaves die and vascular tissue of stems and roots becomes slightly discolored. Warm weather and excessive soil moisture increase disease severity. Verticillium generally damages potatoes only when present at high populations or when root lesion nematodes are also present. Tomato cultivars are resistant to some but not all strains. Controls include:

• selection of resistant cultivars,
• rotation to non-host crops,
• soil solarization, and
• use of black plastic mulch.

Rotations are most effective when the rotational crops do not allow large numbers of Verticillium propagules to be formed. Dry beans and sugar beets are not recommended as rotational crops for this reason. A 3 or 4 year rotation is usually sufficient to reduce disease incidence although microsclerotia persist in the soil for 10 years or more. Reducing root lesion nematode populations helps control Verticillium because this fungus often infects nematode-damaged root systems.

Together, root lesion nematodes and Verticillium cause severe symptom development and lower yields at population densities that have little or no effect with each pathogen individually. Rotating potatoes with sudan grass reduced Verticillium damage to potato stems in Washington.Although fungal populations stayed the same, the number of #1 potatoes increased and potato stems were not attacked.

References

• Scholte, K. 1992. Effect of crop rotation on the incidence of soil-borne fungal diseases of potato. Neth. J. Pl. Path. 98 Supplement 2:93-101.

• Powelson, M.L. and R.C. Rowe. 1993. Biology and management of early dying of potatoes. Annu. Rev. Phytopathol. 31:111-126.

• Schoenemann, J. 1983. Current research on potato diseases. American Vegetable Grower 31(2):32-36.