Ever heard of Bot canker? "Bot" stands for Botryosphaeria which is a plant disease that results in cankers of trees and other woody plants.
This fungal disease can be worse under drought conditions when trees are stressed. Early symptoms like yellowing leaves and a sparse canopy could be mistaken for other issues like Verticillium wilt and Phytophthora root rot. After cankers form on branches and the trunk, the dark wedge-shaped stains inside the wood can help you confirm the cause as Botryosphaeria canker.
Managing Bot canker relies on keeping plants healthy so that they can resist the infection. When planting, choose plants that are well-suited for the location, including soil type and sunlight. Under drought conditions, trees may need supplemental irrigation to stay healthy.
You can read more in the new UC ANR publication Pest Notes: Botryosphaeria Canker by Jim Downer, UC Cooperative Extension Environmental Horticulture Advisor for Ventura County, and plant pathologists Dee Vega, Cal Poly Pomona and Themis Michailides, Kearney Agricultural Research and Extension Center. This free publication has more diagnostic tips and information on management of this disease.
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Author - Associate Director for Urban & Community IPM/ Area Urban IPM Advisor