By O. Neher and C. M. Ocamb
Cause Phoma betae, a fungus that attacks seedlings, leaves, and roots in the field and in storage. It often enters wounds during the growing season and at harvest. The disease is much worse when beets are stressed. The sexual stage of the fungus, Pleospora bjoerlingii can spread the disease within the field and to other fields by producing ascospores while conidia of the asexual stage can infect seed. Beet seed lots with 40% to 50% infection have been found.
Symptoms Seedlings may damp-off. Lesions resemble those of Cercospora leaf spot. Leaves develop small brown spots with black ridges in concentric circles. Lesions become covered with small black spots (pycnidia). Roots at first develop small, depressed, brown lesions in the crown area. These become conical areas of black rot, both in the field and in storage.
Cultural control
- Implement a 3- to 4-year crop rotation.
- Practice good management to control alternate weedy hosts.
- Maintain proper water and nutrient levels during the growing season.
- Avoid wounding roots.
Chemical control Seed treatments.
- Captan 4F at 6 fl oz/100 lb seed plus a dye.
- 42-S Thiram at 8 fl oz/100 lb seed plus a dye. 24-hr reentry.