Q: My tomato plants have wilted from the top. They look like they need to be watered but I know they have been getting enough water. I cut the stem like you suggested and I see a brown ring. What does it mean?
A: It sounds like Fusarium wilt. The earliest symptom is the yellowing of the older, lower leaves. It is a soil borne fungus that attacks tomatoes and other crops. The yellowing process gradually includes more and more of the foliage and is accompanied by wilting of the plant during the hottest part of the day. The wilting becomes more extensive from day to day until the plant collapses and dries up. The vascular tissue of a diseased plant is dark brown in color. This browning often extends far up the stem and is especially noticeable in a petiole scar. This browning of the vascular system is characteristic of the disease and generally can be used for its identification. Fruit infection occasionally occurs and can be detected by the vascular tissue discoloration within the fruit. It is controlled only through the use of resistant varieties. Before you plant a variety, make sure it is resistant to Fusarium wilt. This resistance is denoted by the letter F after the name. Example: Celebrity VFN. A 5-7 year crop rotation will greatly reduce losses on infested land or grow the few plants you have in pots.