Pear trellis rust is caused by the fungus Gymnosporangium sabinae. It was introduced into the United States from Europe in the 1990s and has been progressively spreading through states in both the East and West. The disease affects common pear, callery pear, and several species of juniper/eastern red cedar.
Adult sawflies are often similar in appearance to flies or wasps. The larvae are also similar, though sawflies have one simple eye on each side of the head and five or more pairs of prolegs on their abdomen, whereas butterflies/moths (Lepidoptera) have four pairs of prolegs, and multiple eyes on each side of the head.
Bacterial leaf scorch (BLS) is caused by the bacterium Xylella fastidiosa. This disease impacts certain shade trees resulting in uneven ‘scorching’ of leaf margins in late summer and early fall. The bacteria themselves live in the xylem tissue and gather in clusters called biofilms. These ‘bunches’ of bacteria clog the xylem and block water transport, which leads to the scorch symptoms.
Two common causes of root disease in California are species of the fungus Armillaria and species of Phytophthora, which are fungus-like organisms. There are many differences between the two pathogens, but effective management of both involves creating growing conditions that favor plant vigor and that inhibit the pathogen.
Caused by a fungus, Ceratocystis fagacearum, oak wilt invades the vascular system of trees. The disease can cause rapid decline and even death of infected plants. Susceptibility to this disease varies among oak species; members of the red oak group decline and die quickly following infection, while white oaks tend to be resistant and recover. Live oaks are intermediate in susceptibility to oak wilt and infected trees may recover with early detection and treatment.
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