Cercospora leaf spot (Cercospora cruciferarum
and C. atrogrisea)
Cercospora leaf spot on radishes causes circular to
angular grey or off-white lesions with darkened
(brown to red-brown) margins on cotyledons,
leaves, and petioles. The disease may eventually
result in defoliation, particularly on younger
seedlings. The pathogen survives in crop residues
and can infect cruciferous weeds and volunteer
plants. Tufts of spores are produced in the center
of leaf spots and on overwintering crop residues.
Rain or overhead irrigation is the most important
mechanism of spore dispersal. Conditions for
disease development are optimum in spring and
late summer (temperatures 55-65°F (13-18°C) and
infection is promoted by long periods of leaf
wetness. Deep cultivation and removal of all
cruciferous weeds/crops, along with crop
rotations, may reduce incidence