Cavity spot

Cavity spot is a serious disease of carrots caused by species of Pythium such as P. violae and P. ultimum and species of Rhizoctonia such as R. solani, which are induced by a calcium deficiency, anaerobic bacteria and stress from flooding and high soil temperatures.

Symptoms
Lesions are elliptical, oriented across the breadth of the root, generally smaller than 1cm (½in) in diameter, and no more than 0.25cm (⅛in) deep. These symptoms can be easily confused with damage from nematodes, soil compaction or soil drainage problems.

Treatment
None. Cavity spot does not reduce yield, but will affect the appearance of the roots.

Prevention
Management of Pythium diseases is difficult if the growing season is wet, however, some tolerant varieties are available. Also, precision planting on raised beds, crop rotations to cole crops, onions or potato and improvements to field drainage may help. There is evidence that high nitrogen levels in the soil may also contribute to the problem. Avoiding problem fields is helpful if that option is available. Soil applied fungicides or seed treatments for management of cavity spot may be helpful, however, if soil moisture conditions and disease pressure levels are good for the disease, problems may still occur.