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Botryosphaeria Stem Canker in Desert Willow

Botryosphaeria spp. are responsible for a variety of symptoms on some trees, including, leaf spots, stem cankers and fruit rots. In Arizona they occasionally cause wilting of limbs on desert willow (Chilopsis linearis) as seen above and on Eucalyptus camaldulensis. In cooler climates, they are a problem on apple trees responsible for fruit rots. The practice of pruning apple trees during the summer for fire blight management, or to open canopies to light and air may increase the incidence of infection caused by B. obtusa and B. dothidea by wounding the trees at a time when they may be more vulnerable to canker development due to drought stress.

At present, the recommended control for managing cankers caused by Botryosphaeria spp. is to prune out the affected branches followed by a trunk injection with Fungisol, a systemic fungicide.

Disease Cycle in Apples

The fungus overwinters in pycnidia on dead twigs, cankers and fruit mummies. Ascocarps arise on cankered areas of bark and on dead twigs that have been present on the tree over a year. Although conidia are produced throughout the growing season, ascospores are most common within 4-6 weeks of petal fall. Spores are disseminated by wind, rainsplash, and to some extent, by insects.

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