Brassica black rot is a bacterial disease of brassica crops (such as cabbage, Brussels sprouts, kale) caused by Xanthomonas campestris pv. 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 can 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.
Most often, primary infection occurs when infected seed or transplants enter a field. Some brassica weeds, like mustards and radishes, can also carry and spread the disease. Once established in a field, the disease spreads via splashing water, wind, equipment, workers, and some insects. The bacteria can survive in and on infested soil-bound plant debris that can survive for up to two years. Favorable conditions include high moisture, hot temperatures, and poor airflow.
The black rot disease cycle begins with primary infection, which can occur as early as the seedling stage. The bacteria can survive in or on brassica seeds, infecting seedlings as they grow. These infections may not present with distinct symptoms, or may mimic other forms of stress. If seedlings are grown in a greenhouse, infected flats or soil can be a source of inoculum. Transplants that have been clipped via mowing can carry disease as well. Once a plant is infected, the bacteria can be spread from one plant to another by splashing water, wind, or contact with equipment and some insects. During favorable conditions, the bacteria is able to enter a plant through the hydathodes (water pores on the outer edge of the leaf) or wounds, which can be caused by insects or machinery. Heavy black rot infection can often be followed by secondary soft-rot infections. At the end of a season, the bacteria can survive on seeds, or in soil-bound plant debris.
Cultural management includes scouting regularly to identify the presence of the disease early, before it has had a chance to spread and cause significant damage. The following practices can help mitigate the risk of this disease:
- Plant resistant varieties when possible
- Plant certified disease-free seed (may include process of hot-water seed treatment
- Rotate away from susceptible brassica crops for ≥ 3 years
- Maintain proper spacing between plants
- Plant in areas with good airflow
- Avoid overhead irrigation
- Avoid working in fields when plants are wet
- Manage host weeds
- Remove and destroy infected plants
- Destroy infested plant debris
- Disinfest tools and equipment
Properly-timed copper or biopesticide elicitors such as acibenzolar-S-methyl can also be used to manage disease. For Wisconsin-specific fungicide information, refer to the Commercial Vegetable Production in Wisconsin (A3422), a guide available through the UW Extension Learning Store website. Or, for home garden fungicide recommendations, see Home Vegetable Garden Fungicides (D0062), a fact sheet available through the UW Plant Disease Diagnostic Clinic website. Always follow label directions carefully.
- Bess Dicklow, M., R. Hazzard, A. Cavanagh, and S. Scheufele. 2022. “Brassicas, Black Rot.” Center for Agriculture, Food, and the Environment: UMass Extension Vegetable Program. September 2022. https://ag.umass.edu/vegetable/fact-sheets/brassicas-black-rot.
- Liu, Zeci, Huiping Wang, Jie Wang, Jian Lv, Bojie Xie, Shilei Luo, Shuya Wang, et al. 2022. “Physical, Chemical, and Biological Control of Black Rot of Brassicaceae Vegetables: A Review.” Frontiers in Microbiology 13 (November): 1023826. https://doi.org/10.3389/fmicb.2022.1023826.
- McGrath, Margaret Tuttle. 1994. “Black Rot of Crucifers.” Cornell Vegetable MD Online. November 1994. http://vegetablemdonline.ppath.cornell.edu/factsheets/Crucifers_BR.htm.
- Pape, Andrew. 2021. “Black Rot of Crucifers.” Plant Disease Diagnostics Clinic. May 11, 2021. https://pddc.wisc.edu/2015/07/06/black-rot-of-crucifers/.
- Smart, Christine D., and Holly W. Lange. 2010. “Managing Black Rot of Cabbage and Other Crucifer Crops in Organic Farming Systems.” EOrganic. September 15, 2010. https://eorganic.org/node/4957.
- Vicente, Joana G., and Eric B. Holub. 2013. “Xanthomonas Campestris Pv. Campestris (Cause of Black Rot of Crucifers) in the Genomic Era Is Still a Worldwide Threat to Brassica Crops.” Molecular Plant Pathology 14 (1): 2–18. https://doi.org/10.1111/j.1364-3703.2012.00833.x.
Written by Amanda Gevens and Ariana Abbrescia. Last updated Mar 27, 2023