Brassica Black Rot

Brassica Black Rot is a bacterial disease of brassica crops caused by Xanthomonas campestris py. campestris. It causes V-shaped yellow lesions that move from the outer edges of the leaves inwards, with nearby veins turning black and thickening. Foliar symptoms might appear similar to those of plant stressors including drought, overwatering, or over-fertilization. Once established in the leaves, this disease can cause black discoloration inside the stem, which will become visible when cut. As the disease progresses, the roots may also turn black. This pathogen survives primarily on infected seed, and can persist in soil-bound plant debris for up to two years.  Once established in a field, the disease spreads via splashing water, wind, equipment, workers, and some insects.

Favorable conditions include high moisture and poor airflow. Cultural management involves planting resistant varieties and certified disease-free seed (may include process of hot-water seed treatment), rotating away from susceptible brassica crops for >3 years, maintaining proper spacing between plants, avoiding overhead irrigation and working in fields when plants are wet, managing host weeds and infected debris, and disinfecting tools and equipment. Properly-timed copper or biopesticide elicitors such as acibenzolar-S-methyl  can also be used to manage disease.

Photo Credit: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org