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Verticillium Wilt

Plant disease · Verticillium dahliae and Verticillium albo-atrum

Description​

Verticillium wilt is a soilborne disease caused mainly by the fungi Verticillium dahliae and V. albo-atrum. The fungi enter through roots and grow in the water-conducting tissue, restricting the movement of water through the plant. They affect many vegetables, flowers, shrubs, and trees, including tomatoes, potatoes, strawberries, and maples. Symptoms often begin on older leaves or on just one side of a plant, then spread as the disease progresses. Affected plants may survive but grow poorly, produce less, or decline over several seasons. V. dahliae forms tiny resting structures that can persist in soil for years, even without a susceptible crop. The fungi can spread in infected plants and in soil moved on tools, footwear, or equipment. Disease severity varies with the host, the amount of fungus in the soil, and growing conditions. Because the pathogen lives inside the plant and persists in soil, established infections are difficult to control.

Symptoms​

  • Yellowing leaves
  • Brown or crispy leaf edges
  • Wilting
  • Stunted growth
  • Leaves dropping

How to Identify​

Look for yellowing, browning, and wilting that may start on older leaves or one side of the plant. A cut through the lower stem or a larger branch may reveal brown streaks or a brown ring in the water-conducting tissue. This discoloration is a clue, not proof: Fusarium wilt can look similar. Verticillium often develops in comparatively cool conditions, while Fusarium wilt is generally favored by warmer soil, but temperature alone cannot distinguish them. Drought and root damage can also cause wilting, usually without vascular browning. For a reliable diagnosis, send a freshly symptomatic stem and relevant plant details to a plant diagnostic laboratory.

Prevention​

Choose cultivars labeled resistant to Verticillium wilt where available, and buy healthy plants from reputable sources. In grafted crops, use a resistant rootstock. Avoid bringing soil from affected beds into clean areas; clean soil from tools, footwear, and equipment before moving between beds. Remove susceptible weeds and volunteer plants that may maintain the fungus. Rotate susceptible annual crops with nonhost crops, but do not rely on a short rotation: the fungus can persist for years, and many plants are hosts. Keep plants vigorous with appropriate watering and drainage, and avoid excessive nitrogen fertilizer. If a bed has a confirmed history of disease, grow resistant or nonhost plants there instead. In warm, sunny climates, soil solarization may reduce fungus near the surface but will not reliably eliminate it.

Treatment​

There is no reliable cure for an infected plant. First, reduce stress: water deeply when needed, mulch to moderate soil moisture, and maintain good drainage. These steps may help a mildly affected plant continue growing, but they will not remove the fungus. Prune dead branches from woody plants, disinfecting tools between plants; pruning cannot cure an infection in the roots or trunk. Remove annual plants that are severely affected, taking out as much of the root system as practical. Bag infected material for disposal rather than putting it in a home compost pile, and avoid moving contaminated soil. Do not replant a susceptible species in the same spot; choose a resistant cultivar or a suitable nonhost instead. Soil solarization can sometimes lower disease pressure before replanting, particularly in hot, sunny weather, but results vary. Fungicide sprays do not reach or reliably control the fungus inside infected plants.

Plants Affected​

Artichoke, Catalpa, Eggplant, Japanese Maple, Maple, Mint, Northern Catalpa, Norway Maple, Red Maple, Redbud, Rubus, Silver Maple, Smokebush, Southern Catalpa, Strawberry, Sugar Maple, Sumac, Sycamore Maple, Syringa, Tulip Tree, Yellow Poplar

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