Poster Sessions Concurrent Sessions Conference Proceedings Oak Symposium Home This paper was not included in the Symposium Proceedings.	Pre-Symposium Abstract of Paper Insect and Disease Pests that can cause SOD-Like Symptoms on Oaks Bruce W. Hagen California Department of Forestry and Fire Protection, 135 Ridgway Ave., Santa Rosa, CA 95404; (707) 576-2936; bruce_hagen@fire.ca.gov The death of individual oaks is not unusual. Oaks do indeed die of natural causes. California's native oaks live with a multitude of plant pathogens and arthropod (insect and mite) pests throughout their lives. As many as 800 insects and more than 200 diseases have been reported on oaks (Sweiki, Bernhardt and Arnold, 1990). All life stages and virtually all parts of oaks are affected. With the exception of sudden oak death, few of these pests cause serious damage in undisturbed oak woodlands. In general, stressed, severely disturbed or aging trees are most at risk. Sudden oak death (SOD) is characterized by bleeding cankers on the lower trunk of susceptible oaks. The bleeding has been described as a dark, thick exudate (droplets) often surrounded by a diffuse staining. Irregularly shaped patches of dead, discolored phloem can be seen when the outer surface of the bark is cut away. A thin, dark "zone" line occurs at the periphery of the lesion. Decline is relatively rapid; generally occurring over one to two seasons. The foliage of affected trees may brown suddenly or gradually thin. Oak bark beetles and oak ambrosia beetles are commonly associated with trees killed or injured by SOD. Root diseases, e.g., Armillaria spp. and Phytophthora spp. can cause similar symptoms, e.g., sudden or gradual decline and bleeding and basal lesions. Occasional bleeding, bark-lesions (cankers) white mycelial fans under the bark and mushrooms growing near the root crown in the winter characterize Armillaria root disease. Phytophthora root disease is typified by oozing or vertical, "streak" stains and bark-lesions similar to those caused by the SOD pathogen. Root diseases occur mostly in urban area, particularly in irrigated settings and on trees with buried root crowns. Trees on sites with drainage problems or where seasonal flooding occurs are more likely to be affected. Crown thinning, defoliation and leaf browning can also be caused by defoliators (oak worm, tussock moth, leaf miners, etc., certain leaf and twig diseases (cryptocline and diplodia canker), gall wasps, root loss injury, prolonged drought or heat injury. Bleeding, weeping, oozing on the trunk is often associated with borers, e.g., carpenterworm, sycamore borer, oak bark beetles, Pacific flatheaded borer and oak cordwood borer. The presence of frass (sawdust and fecal pellets) indicates the presence of certain borers. Borers are unable to attack healthy, vigorous oaks. Canker rot organisms that invade the bark after rotting the heart and sapwood are often associated with weeping or oozing. Dying oaks are typically colonized by oak bark and ambrosia beetles. Boring dust (frass), indicating attack, collects below and/or around pinhole-sized entry tunnels made by the beetles. Boring dust also accumulates in bark crevices and on the ground. Dying and dead oaks are also commonly colonized by Hypoxylon thouarsianum, a wood rotting fungus characterized by black, dome-shaped fungal fruiting-bodies up to two inches in diameter typically appear on the lower trunk and large branches.
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