Identification of measures for prevention of black spots in organically produced stored carrots

In the Netherlands winter carrot for the fresh market is a cash crop for many organic growers of field vegetables. In the last few years blackish spots have been observed during storage of carrot roots. An inventory was carried out in 2001/2002 and 2002/2003 including in total 42 carrot lots from 22 growers. Statistical analysis was performed by multiple regression analysis to identify factors and variables that best explained the occurrence of black spots on stored carrots. Rhexocercosporidium carotae was the dominating pathogen in black spots of carrots harvested in 2001. From carrots harvested in 2002, Alternaria radicina was isolated most frequently, followed by A. dauci and R. carotae. Multiple regression analysis indicated that the occurrence of R. carotae was associated with wild umbelliferous plants or carrot production during the previous year in the neighbourhood of the investigated carrot fields. A high occurrence of the symptoms of black spots was associated with increasing damage caused during harvest or with higher temperatures during harvest