Cause A complex of two viruses, Carrot mottle virus and Carrot red leaf virus, which are transmitted together by the carrot-willow aphid, Cavariella aegopodii. In areas where wild carrots or cultivated carrots survive year-round, both the virus complex and the vector aphid can overwinter on carrot plants and transmit the disease to commercial carrot and parsley crops early in the next growing season. In colder areas, the aphids overwinter on willow and have to acquire the viruses from an infected host plant before they can transmit. Both of these viruses can infect parsley and cilantro but since cilantro is not a host for the aphid vector, it is unlikely to act as a source for virus spread.
Symptoms Symptoms on the tops are similar to those of the aster yellows disease and include central rosette, severe stunting and deformation, and yellowish and reddish leaf margins. Roots are not malformed as when carrots are infected by aster yellows.
- Separate new seedings of carrot and parsley as much as possible from overwintering carrot seed crops or wild umbelliferous plants.
- Do not allow aphid populations to build up on carrots. Refer to the PNW Insect Management Handbook for details.
- Avoid late planting when migrating aphids are numerous.
References Howell, W.F., and Mink, G.I. 1974. Carrot motley dwarf in the Pacific Northwest. Plant Disease Reporter 58:766.
Murrant, A.F. 1975. Occurrence of mottle and red leaf components of carrot motley dwarf disease in British Columbia. Canadian Plant Disease Survey 55:103-105.
Watson, M.T., Tian, T., Estabrook, E., and Falk, B.W. 1998. A small RNA resembling the beet western yellows luteovirus ST9-associated RNA is a component of the California carrot motley dwarf complex. Phytopathology 88:164-170.