Suppression of Bacterial Leaf Scorch Symptoms in American Elm Through Oxytetracycline Microinjection

Abstract

American elms with bacterial-associated leaf scorch (ELS) were injected with oxytetracycline (OTC) to determine if the antibiotic would cause a delay in symptom onset or a remission of symptoms. Degree of symptom expression and presence of fastidious, xylem-inhabiting bacteria were determined in August 1982. Eleven symptomatic trees were injected in August 1982 with OTC (40 mg a.i./cm dbh) delivered via Mauget capsules. OTC was injected at 40 mg a.i./cm dbh into 14 trees and at 80 mg a.i./cm dbh into 8 trees using a pipette injection technique. Ten untreated, symptomatic trees served as controls. In June 1983, all OTC treated trees were injected using prefilled Mauget capsules at dosage levels of 50 mg a.i./cm dbh or 80 mg a.i./cm dbh. By July, symptoms appeared in 7 of 10 untreated trees but only in 2 of the remaining 29 OTC-treated trees. By late August, symptoms were absent or reduced in 22 of 23 trees treated at the low OTC levels, and 3 of 6 trees treated at the high OTC level. Symptom remission was most apparent in trees which had less than 20% of the canopy leaf area affected with ELS prior to treatment. Delay of symptom onset and symptom remission support the role of the fastidious, xylem-inhabiting bacterium as the causal agent of ELS.