Utah State University Extension issued guidance on September 4, 2026, regarding the management of anthracnose and fire blight, two diseases that impact common ornamental species. The technical documentation provides specific identification symptoms and integrated pest management strategies to help mitigate the spread of these pathogens in various environments.
Anthracnose Symptoms and Host Species
Anthracnose, caused by species such as Apiognomonia, Discula, and Kabatiella, affects sycamore, maple, and oak trees. According to Utah State University Extension, all three host species exhibit irregular-shaped necrotic lesions on leaves, which frequently appear on the leaf margins or along the veins.
On sycamore trees, the disease causes new shoots to exhibit wilting and dieback. In more advanced stages, cankers may develop on the trunk and branches. Repeated dieback can lead to the formation of witches' brooms, which are clusters of live and dead branches. In maple and oak trees, the disease can cause premature leaf drop during the late spring or early summer, while oak trees may experience dieback of expanding leaves and newly emerging shoots.
Anthracnose Disease Cycle and Management
The anthracnose disease cycle begins as the pathogen overwinters in fruit, twigs, buds, or fallen leaves and petioles, depending on the specific host and species. Spores are dispersed through the air or by water during leaf expansion, particularly during spring rains when temperatures remain between 50 and 68 degrees F. Infected leaves may further spread the disease to healthy foliage during rain events throughout the growing season.
To manage anthracnose, Utah State University Extension recommends maintaining overall tree health through proper watering and fertilization. Specific mitigation steps include pruning out branches that exhibit cankers or dieback and raking and destroying fallen leaves to eliminate overwintering inoculum. For preventative measures, the Extension suggests applying fungicides before leaf buds open, repeating the application every 10 to 14 days until conditions are no longer favorable for the disease.
Fire Blight Identification and Symptoms
Fire blight, caused by the bacterium Erwinia amylovora, primarily targets plants in the Rosaceae family, which includes various roses. According to Utah State University Extension, the disease presents distinct symptoms during the spring, such as flowers turning brown and dying.
During the spring, shoots and leaves may begin to die back from the tips, often resulting in a bent tip known as a "shepherd's crook." As infections become more established, they can develop cankers on the main trunk or on large branches. These cankers may appear wet when bacteria are actively oozing from them.
Fire Blight Transmission and Prevention
The bacteria responsible for fire blight overwinter within infected tissues at the margins of cankers. Disease growth typically begins in the spring as the tree breaks dormancy. The bacteria can be spread to blossoms during the bloom period or to shoots through natural openings or physical damage. Bacterial ooze can also be spread by flies and bees during pollination or splashed by water.
Trees remain susceptible to infection until new growth ceases, and succulent growth, such as root sprouts, can be infected at any time. Utah State University Extension recommends pruning infected shoots at least 12 inches below the symptomatic area to ensure bacteria that have moved beyond the visible area are removed. It is critical to disinfect pruning tools between every cut using a solution of 70% alcohol, 10% bleach, or disinfecting wipes to prevent spreading the bacteria to healthy plants. Additionally, copper products may be applied to cankers during the dormant season, and antibiotics can be used in the spring to prevent infections in blossoms. Residents can monitor risk for ornamental trees through the university's fire blight risk forecasting system at climate.usurf.usu.edu/traps.
