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Ecology and Epidemiology

Epidemiology and Control of a Blight of Juniperus virginiana Caused by Cercospora sequoiae var. juniperi. Glenn W. Peterson, Plant Pathologist, Rocky Mountain Forest and Range Experiment Station, U.S. Department of Agriculture, Forest Service, Lincoln, NB 68503; Phytopathology 67:234-238. Accepted for publication 26 August 1976. Copyright © 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-234.

In eastern Nebraska, spores of Cercospora sequoiae var. juniperi were trapped as early as late April, but dispersal was not abundant until late May or early June and it extended into October. Spores were dispersed only during rainy periods. There was no evidence of long-distance dispersal; no spores were collected in volumetric traps 2 m from infected trees. Germination of spores began within 6 hr and after 24 hr was more than 90% over the range 16 to 28 C. Germ tube growth was optimum at 24-26 C. First infection of spur leaves of Juniperus virginiana occurred during the period 14-28 July in 1971 and 21 June -5 July in 1972. Symptoms on spur leaves were first observed 8 August in 1971, 19 July in 1972, and 21 July in 1973. Only previous years’ spur leaves and both current and previous years’ juvenile leaves became infected. Whip leaves, the characteristic foliage of extremities of long shoots on secondary and tertiary branches, were not infected. Results provide a sound basis for determining when protective fungicides should be applied in eastern Nebraska.