As the vegetable growing season winds down, now is a good time to dig up plants in high tunnels and open fields and determine the health of the roots. Root diseases that may not kill plants outright can nonetheless stunt plant growth and reduce yields. Look for plants that appear less vigorous than others and remove them with a shovel, taking care to maintain root integrity. Shake off the soil and rinse the roots gently with water. Then examine roots for symptoms.
While some soilborne diseases such as Phytophthora blight can “explode” in the field from relatively low initial inoculum levels, many others build up slowly from season to season. Root-knot, caused by the the plant pathogenic nematode Meloidogyne spp., is increasing in prevalence in Ohio in high tunnel tomatoes and other crops in open fields. Root-knot is fairly easy to identify – galls are clearly visible on roots. The Northern root-knot nematode, which predominates in northern Ohio, causes small galls, while the southern species, which occurs in southern Ohio, causes large galls. Since root-knot nematodes have a very broad host range, crop rotation may not be helpful, although certain cover crops such as sudangrass are toxic to nematodes, and wheat and corn are not hosts of northern root-knot nematodes. Anaerobic soil disinfestation (ASD) is highly effective against root-knot.
End-of-season root health checks are especially important for high tunnel tomatoes, which are often produced in the same soil year after year. Root-knot, Verticillium wilt, corky root rot, black dot root rot, and Pythium root rot are among the root diseases that can predominate in long-term non-rotated tomatoes. The roots should be evaluated every year to assess disease development and the need for control measures such as grafting on disease-resistant rootstocks and ASD. A fact sheet describing tomato soil borne diseases and their management can be found here.