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Natural Biological Control of Oak Wilt in Arkansas. F. H. Tainter, Assistant Professor, Department of Plant Pathology, University of Arkansas, Fayetteville 72701; W. D. Gubler, Research Assistant, Department of Plant Pathology, University of Arkansas, Fayetteville 72701. Phytopathology 63:1027-1034. Accepted for publication 5 February 1973. DOI: 10.1094/Phyto-63-1027.

Three species of red oak and two species of white oak (Quercus spp.) were inoculated with a spore suspension of Ceratocystis fagacearum and then harvested monthly. The fungus was recovered at a very low rate after 14 months. All inoculated red oak trees wilted and died. In the red oak group, C. fagacearum spores apparently moved rapidly upward into branches of the crown, and the pathogen was readily isolated up to 8 months after inoculation. Lowered survival of the oak wilt fungus after 8 months is believed due to high summer temperatures, drying of the branches, and sapwood invasion by species of Hypoxylon (mostly H. atropunctatum). C. fagacearum seldom colonized trunk sapwood or formed mycelial mats and pressure pads. Within 2 months after inoculation with C. fagacearum the conidial stage of Hypoxylon was apparent under sloughing bark on the trunks of several red oak trees; within 4 months Hypoxylon had begun to produce in many trees a characteristic yellow decay with black zone lines which probably prevented subsequent colonization by C. fagacearum. Trunks of trees containing C. fagacearum pressure pads were about 50% wetter than were trees with Hypoxylon decay. Few trees of the inoculated white oak group wilted, but C. fagacearum was recovered at low levels from branches during the entire 14-month period. Hypoxylon was never found colonizing white oak trees inoculated with C. fagacearum. Maps associating the southern distribution of oak wilt with isotherms and land forms are presented.