Blackleg can also infect the crop in storage. Blackleg will not survive on seed that is soaked in 122 degrees F water for 25 minutes. Infected transplants are also often sources of blackleg. Sheep manure can be a source of blackleg inoculum if the sheep have grazed on infected plants. Blackleg symptoms are worse on plants also damaged by herbicide.
Black rot is caused by a bacteria to which all brassicas are susceptible.
This bacteria is seed-borne, but can also overwinter on weeds and crop debris. Worldwide, black rot is considered to be the most important disease of crucifers. Infected leaves develop a wedge shaped yellowing on the margins, often followed by blackening of the veins and dying of V-shaped sections of the leaves. Under warm, humid conditions, symptoms appear 10 to 14 days after infection. Black rot may not appear when temperatur es are low, but spreads rapidly during periods of rain and high temperatures.