Black rot is a disease in cole crops caused by bacterium, Xanthomonas campestris pv. Campestris. The pathogen can enter the field on transplants or seeds, and can stay in the soil for over a year where it survives on debris and weeds in the Brassicaceae family. The bacteria move primarily with water and can enter the plant through pores naturally present on the leaf surface. It can also be spread by workers and equipment moving through the field/greenhouse, and can enter the leaves through damage caused by wind, insects and other mechanical injuries.The bacteria need a temperature of 77 degrees and above. While it may seem like the weather in desert is not humid enough for bacteria to become an epidemic, it is not something that should be ignored. The microclimate in the field with the crop canopy being dense, foggy mornings, increased field activity can be conducible for disease development.
Disease management include getting rid of infected plants/tissue, increasing distance between fields and choosing well-drained, controlling weeds especially in mustard family such shepherd’s purse, wild mustard, pepper weed etc. Soil fumigation is effective but may not be economically feasible. Best management practice starts with disease-free seed; hot water treatment can reduce the likelihood that the bacteria will enter the field through the seed. Starting with healthy transplant is equally important.
The disease is a bigger problem in greenhouse than in fields. Greenhouse sanitation is important and includes keeping plant tissue from previous crops out of the transplant production area, as any soil or plant residue could be harboring bacteria and other pathogens. Use new plug trays or clean used trays with heat or a greenhouse disinfectant that is refreshed frequently. Visually assess or test young plants for black rot before transplanting.