| | Causal Organism: Apiosporina morbosa
Crops Affected: all plants within the genus Prunus, including various species of cherries (chokecherry, Nanking cherry, pin cherry, sand cherry, sour cherry, etc.), plums, almond, etc.
Disease Cycle:
- Ascospores are produced on mature galls in the spring, infecting growing points
- Infection causes an increase in xylem and phloem cells in the stem
- The disease will develop internally and externally
- Galls will grow in size each year, producing spores annually
- Plant structure is affected and branch strength may be reduced
- Eventually, plants may die
- A single infected tree or bush can infect a wide area
Symptoms:
- The most recognizable symptom is the presence of a black tar-like swelling on branches of infected plants
- Sometimes vulgarly described as resembling "poop-on-a-stick"
- Initial symptoms include a small swelling or gall at a succulent growing point or fruit spur
- Swellings grow in size and eventually become ruptured, hard and black
- Galls may be 6 or more inches in length
- Galls may also occur at branch junction points and on scaffold limbs
- Galls may eventually be colonized by secondary fungi, which can reduce sporulation
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Swollen tar-like galls of various sizes are visible on branches and branch junctions |
Photos by Tricia Simon |
Management:
- Remove sources of inoculum in adjacent areas
- Prune out infected branches during the dormant season, when plants are dormant and galls are highly visible
- Galls should be pruned out, with cuts being made at least 6 inches beyond obviously infected materials
- Pruning cuts should be made to an appropriate point (healthy collar, etc.)
- If possible, pruning tools may be disinfected between cuts, however this may be difficult or impractical in many situations
- Destroy infected material by burning, burial and/or proper composting, or removal from the site
- Ensure plants are healthy and free from stress
- Ensure adequate canopy ventilation
- Chemical controls are limited, fairly ineffective and expensive
- Consider hiring a certified arborist for complex pruning activities
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