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Disease Control and Pest Management

Symptom Remission in X-Diseased Peach Trees as Affected by Date, Method, and Rate of Application of Oxytetracycline-HCl. D. A. Rosenberger, Research Assistant, Department of Botany and Plant Pathology, Michigan State University, East Lansing, MI 48824; A. L. Jones, Associate Professor, Department of Botany and Plant Pathology, Michigan State University, East Lansing, MI 48824. Phytopathology 67:277-282. Accepted for publication 4 August 1976. Copyright © 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-277.

X-diseased peach trees with 9- to 17-cm trunk diameters were treated at various times during the growing season with five rates of oxytetracycline-HCl (OTC). Injections of 1.25, 2.5, and 3.75 g OTC per tree in September induced remission of symptoms for one year, whereas spring, summer, or fall injections of 0.5 or 0.9 g OTC per tree were less effective. Injections of 1.25 and 2.5 g OTC per tree in October and November were phytotoxic. Injections of dilute OTC by infusion and by pressure, and concentrated OTC pipetted directly into holes drilled in the trunks, all provided remission of foliar symptoms for one year. Terramycinlike activity (TLA) was greatest in leaves from trees injected by infusion. Injection of concentrated OTC was the most rapid and convenient method tested, but 2.5 g OTC in concentrated form caused some necrosis around the injection holes in the tree trunks. Increasing solution concentration by reducing the volume of solution injected did not reduce TLA activity in leaves except for the most concentrated treatment, 1.25 g OTC injected in 10 ml of solution. Terramycinlike activity in leaves declined rapidly following September injections and TLA in fruit from September-treated trees was below a desired residue tolerance of 0.1 μg/g fruit tissue.