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Development of Canker on Ulmus pumila Related to Month of Inoculation with Botryodiplodia hypodermia. Jerry W. Riffle, Plant Pathologist, Rocky Mountain Forest and Range Experiment Station, U.S. Department of Agriculture, Forest Service, Lincoln, NE 68503; Phytopathology 68:1115-1119. Accepted for publication 10 February 1978. Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-1115.

Botryodiplodia hypodermia was confirmed, by wound-inoculation of 1-yr-old seedlings, as the cause of a canker disease of Ulmus pumila. Canker development was observed on 6-yr-old U. pumila trees in Nebraska that were inoculated with mycelial disks of a B. hypodermia isolate at approximately monthly intervals from March 1974 through February 1975. The fungus infected all trees that were wound-inoculated in March-September. Cankers 7.6 to 12.8 cm long developed during the first growing season on trees inoculated in March-May; by the end of the second growing season, 75% of these cankers were callused over. On trees wound-inoculated in July-September, the fungus produced numerous pycnidia on 89% of the cankers, which were 48.8 to 72.5 cm long by the end of the first growing season. These cankers enlarged by the end of the second growing season and caused dieback or mortality of 94% of the trees. Extensive adventitious sprouting occurred near the junction of dead and live tissues on more than 80% of the trees that were wound-inoculated in July-September. Only 52% of trees that were wound-inoculated in November-February were cankered by April 1975, but most of these cankers were callused over by October 1975.

Additional keywords: windbreaks, Siberian elm.