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Oak wilt disease
Oak Wilt Disease (OWD), caused by the fungus Ceratocystis fagacearum, kills all native species of oak trees.  The pathogen is believed to be native to the United States and was first recognized as an important disease in 1944 in Wisconsin.  It has been found in 21 states throughout the Midwest, Northeast and Texas in native stands. The disease has not been found in Oregon or any western states to date.
Ceratocystis fagacearum (Microascales, Ophiostomataceae) grows into and throughout the water conductive tissues (xylem) of the host. This process interferes with water uptake by plugging the vessels, causing wilting which often results in tree death. The fungus overwinters as mycelium in still-living, infested trees and as fungus pads on dead trees. The fungus can be spread more than a mile by at least two groups of insects: sap beetles (Nitidulidae) and bark beetles (Scolytidae). Tree to tree spread through natural root grafts readily occurs as well.
All oaks are susceptible. Oaks in the red-black oak group are extremely susceptible and can die within a few weeks of infection. Oaks in the white group are more tolerant of the disease and disease development progresses more slowly, sometimes confined to one small branch.

A quarantine was established against OWD on April 1, 1976 and includes all states and districts of the United States.  All rooted trees, seedling plants, cuttings, scions, bark, leaf mold, roots, or other unpeeled parts, except seed of all species of oak (Quercus spp.), chestnut (Castanea spp.), chinquapin (Castanopsis spp) and tanbark oak (Lithocarpus densiflora) are included.   These commodities may be permitted entry into Oregon provided each lot or shipment is accompanied by a certificate issued by an official agency of the state of origin certifying that all commodities covered by the certificate are free of OWD and are a product of the state from which shipped or of another state, neither of which is known to have oak wilt disease.