Blackarm is a bacterial disease that affects cotton. It is caused by the bacterium Xanthomonas campestris pv. malvacearum. The disease affects the leaves, stems, and bolls of the cotton plant, causing dark, water-soaked lesions that can eventually lead to defoliation and yield loss. The bacteria can survive in soil and plant debris, and can be spread by wind, rain, and agricultural practices such as pruning and harvesting.