Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu
One common disease problem of tomatoes grown in greenhouses is Fusarium crown and root rot. The disease can also be a problem in field production. Symptoms of Fusarium crown and root rot are tan to dark brown dry lesions that develop at the soil line and advance upward. The necrosis on the stem surface extends into the vascular system. As a result of damage to the stem and roots, the foliage becomes chlorotic (yellow) and plants wilt and are stunted.
The pathogen (Fusarium oxysporum f. sp. radicis-lycopersici) also causes disease on legumes, cabbage, carrots, onions, some cucurbits and other plants. Factors that favor the Fusarium crown and root rot are low soil pH, ammonium nitrogen fertilizers, and the presence of other root rots. It is often also associated with sterilized soils.
There are some resistant cultivars available. A good table that lists cultivars that are resistant to Fusarium crown and root rot has been compiled by Dr. Meg McGrath at Cornell and is online at (http://vegetablemdonline.ppath.cornell.edu/Tables/TableList.htm). Grafting to a resistant rootstock is also effective. Sanitation is critical and disinfectants should be used between successive greenhouse crops. Rotate away from alternative hosts between crops in both greenhouse and field production. In addition biological controls containing the agent Trichoderma harzianum, such as Plantshield or Rootshield, have some suppressive activity. Enhancing the microbial activity of soils with organic amendments will also suppress the disease and favor biocontrols.
Fusarium crown rot.
Image from Texas A&M AgriLife Extension