This two-year investigative study showed that there were five different types of carrot crown problems that reduce carrot returns to growers: ring crown rot, smooth crown rot, corky crown rot, soft watery crown rot and black ring.

All except black ring were major defects that will end up in waste bins. Carrots that have black rings in the crowns are downgraded to lower-grade carrots and sold at less than half the premium grade carrot values.

Soil environment has a major influence in crown rot disease development. Ground prepared and crops sown under wet weather conditions have increased incidence of crown rots, as well as other major defects such as forked and misshapen carrots.

High levels of stones, cloddy soil, poor drainage and soil crusting contribute to increased levels of ring crown rot and smooth crown rot. Corky crown rot appeared to be related to exposure of carrot crowns to fluctuating surface soil moisture and temperature.

In a study on irrigation, low soil moisture (12mm at weekly intervals) at the 6 to 9 leaf stages followed by 30mm of irrigation at weekly intervals from 9 leaf to harvest increased crown rot incidence.