Bacterial canker of avocado— Xanthomonas campestris
Bacterial canker is a widespread but relatively unimportant disease in California avocados. Most affected trees will perform well if they are provided with a good growing environment and proper cultural care.
Identification
Bacterial cankers appear as slightly sunken, circular to irregularly shaped, dark areas on bark. These lesions vary from about 1 to 4 inches in diameter. Bark around cankers may crack. Fluid commonly oozes from the cankers and dries, leaving a white powder over or around the lesion. Cankers usually appear first near the base of a limb or trunk and commonly spread in an upward line on one side of the trunk or branch.
Cutting under the surface of affected bark will reveal a decayed, reddish brown necrotic area that may contain liquid. Dark streaks in the wood radiate outward both above and below the lesion. These necrotic streaks are usually in the bark cortex or xylem, but they sometimes extend deeper into the center of the branch or trunk.
Life cycle
Xanthomonas campestris is a common bacterium on avocado leaves and green twigs where it appears to be harmless. Its reproduction and spread are favored by wet plants and humid conditions. It can infect through bark wounds and branch stubs. This leads to systemic colonization of the vascular system. Once trees are infected, drought stress and boron deficiency may promote the development of bacterial canker disease symptoms.
Damage
Severely affected trees may have pale, sparse foliage and low fruit yields on one branch or the entire tree, but this is rare. Sometimes a newly planted tree will become stunted if canker lesions are abundant. New branches may grow from buds below the cankered parts, resulting in an odd growth appearance.
Solutions
This disease is generally a minor problem. No control measures are required on well-established trees. If the disease is severe and fruit yield is affected, consider removing and replacing the tree. If available, use certified, disease-free nursery stock obtained from a reputable, commercial supplier.
Provide trees with a good growing environment and appropriate cultural care to keep them healthy. Provide the appropriate amount and frequency of irrigation based on rigorous methods, such as according to local evapotranspiration (ET) rates or the use of soil moisture monitoring devices such as tensiometers.
If cankers are confined to one or a few branches, these can be pruned off. If the tree is otherwise performing satisfactorily, the cankers can be ignored.
Adapted from Integrated Pest Management for Avocados and Pest Management Guidelines: Avocados, University of California Statewide Integrated Pest Management Program (UC IPM). |
