See:
Carrot (Daucus carota) - Aster Yellows
Cause Spiroplasma citri, which is spread by leafhoppers, has been reported in carrots in Washington state. This pathogen also occurs in hemp, brassicas, tree fruits, and ornamental flowering plants including periwinkle (Catharanthus roseus).
Symptoms Leaves take on yellow-purple discoloration on leaf margins as well as dark purple leaves and petioles. There is a general stunting of shoots and taproots as well as formation of secondary taproots. Carrots will also show a formation of long, bunchy, fibrous secondary roots.
Cultural control
- Remove infected plants as soon as they are detected.
- Control measures against the leafhopper vectors have reduced disease in some areas but are economical only in areas with significant crop losses. For details of materials and application rates, see the PNW Insect Management Handbook.
References Bove, J.M., Renaudin, J., Saillard, C., Foissac, X., and Garnier, M. 2003. Spiroplasma Citri, A plant pathogenic Mollicute: Relationships with its two hosts, the plant and the leafhopper vector. Annual Review of Phytopathology 41:483-500.
Lee, I.-M., Bottner, K.D., Munyaneza, J.E., Davis, R.E., Crosslin, J.M., du Toit, L.J., and Crosby, T. 2006. Carrot purple leaf: A new spiroplasmal disease associated with carrots in Washington state. Plant Disease 90:989-993.