Cause Verticillium dahliae, a soilborne fungus that enter through roots, invade the stem's xylem system, and cut off the water supply. Toxins are also produced, which, along with xylem occlusion, result in wilt symptoms. After the plant dies, the fungus colonizes the plant tissues and produces persistent survival structures. The disease is found most often in outdoor chrysanthemums, but greenhouse chrysanthemums also may be attacked.
Symptoms Foliage yellows and wilts conspicuously, especially near the margins, then leaves brown and die from the base of the plant upward. Infected plants are stunted and often fail to produce flowers. In other cases, the general wilting of the entire plant does not occur; instead, interveinal tissue in leaves becomes a pale yellow-green and finally brown. Discolored brown areas also appear in stems.
- In the greenhouse, sterilize soil previously used for growing mums. Steam 30 min at 140°F. Or use a sterile soilless potting mix.
- Obtain cuttings only from healthy plants.
- Use resistant cultivars when possible.
- Rogue diseased plants early.
Reference Alexander, S.J. and Hall, R. 1974. Verticillium wilt of chrysanthemum: anatomical observations on colonization of roots, stem, and leaves. Canadian Journal of Botany 52:783-789.