Seasonal weather patterns also have a major impact on carrot root diseases. A soil test for pH, salinity and nutrient levels is also a valuable tool. Diseases such as crown rot, violet root rot, Sclerotinia white mold, cavity spot, Pythium root dieback and aster yellows are the most common diseases in Ontario. Crown rot and violet root rot are more common on mineral soils in southern Ontario, however, they are also found in muck soils. Forked and split carrots can be caused by several different problems including nematodes, disease organisms and inconsistent soil conditions.
Diagnosis is usually a process of elimination and assessment of detailed monitoring information.
Crater rot caused by Rhizoctonia carotae is rare in Ontario and tends to be more of a storage disease. Most of the diseases that affect carrot roots are soil-borne diseases which are greatly influenced by soil temperature, soil moisture, nutrition levels and sometimes variety with the exception of aster yellows. Aster yellows is a mycoplasma-like organism transmitted to carrots by the aster leafhopper. It is believed that infections can occur early in the growing season during wet periods, however, symptoms may not be detected until later in the season. Control of this disease is nearly impossible if late summer and fall conditions are wet.