Citrus Canker
Xanthomonas citri subsp. citri
Overview
Citrus canker is a bacterial disease caused by Xanthomonas citri subsp. citri that produces eruptive lesions on leaves, stems, and fruit of citrus and related plants. It spreads by wind-blown rain, contaminated tools, people, and equipment. Warm, wet, windy weather drives outbreaks. The disease is under quarantine or eradication programs in some regions. Even where it is established, canker reduces fruit quality and increases leaf and fruit drop, especially on susceptible sweet oranges, grapefruit, and some specialty citrus.
Symptoms
Raised, corky, tan lesions with water-soaked margins appear on both sides of leaves and on fruit and twigs. A yellow halo often surrounds leaf spots. Severely infected leaves yellow and drop. Fruit lesions are scabby and reduce marketability though the fruit interior may remain edible. Twig dieback occurs on heavily infected shoots. Lesions can resemble other citrus spots but the raised, crater-like texture is characteristic of canker.
Environmental Conditions
Humid
Prevention
Buy nursery stock from certified, inspected sources. Avoid working citrus trees when foliage is wet. Clean tools, hands, and equipment before moving between plantings. Plant less susceptible varieties and rootstocks where canker is endemic. Maintain windbreaks and avoid dense, poorly ventilated hedges of citrus. Keep trees healthy with balanced nutrition so they better tolerate defoliation, but do not over-fertilize with nitrogen that produces soft, highly susceptible flush.
Management
Follow local agricultural regulations; in quarantine areas, do not move citrus material without guidance. Prune out infected shoots during dry weather and disinfect tools. Copper sprays provide protective suppression when timed around rainy periods but do not cure existing lesions. Reduce wind exposure with living windbreaks where appropriate. Remove chronically infected, highly susceptible trees that continually re-infect healthier plantings. Dispose of prunings according to local rules rather than composting them openly.