Description
These fungi (Verticillium species and Fusarium species) cause wilting, stem and leaf discoloration, and the death of many plants. Both types of fungi live in the soil for years, even after the host plants have died. Fusarium thrives in warm soils, and is most severe in the southern states. Verticillium is more of a problem in the cooler soils of the northern states. They both infect annual vegetables, flowers, and herbaceous perennials. Verticillium also infects many woody shrubs, and ornamental, fruit, and nut trees. Infection begins when fungal strands penetrate the roots of a susceptible plant. The fungus spreads up into the water-conducting vessels in the stems and leaves and breaks down some of the plant cells, producing gels and gums. The accumulation of gels, gums, cell debris, and fungal strands and spores in the vessels reduces the water flow up into the leaves. The clogging results in wilting, leaf and stem discoloration, and eventually the death of the plant. The fungus also produces toxins that move up into uninfected leaves. These toxins interfere with photosynthesis and the production of chlorophyll, the green pigment necessary for plant health and growth.
Control
Once plants have been infected they usually die, but diseased flowers and vegetables often last through the season if they are cared for properly. Replace infected plants with varieties resistant to these wilt diseases (see Flowers Susceptible to Fusarium Wilts and Plants Resistant to Verticillium Wilt). If you want to use susceptible plants, eliminate the fungus from the soil by fumigation. (For information on soil fumigation, see Soil Fumigation and Solarization.)
