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Chemical Control of Rhabdocline Needle Cast of Douglas-Fir. H. L. Morton, Professor, Forest Resources Program, School of Natural Resources, University of Michigan, Ann Arbor 48109. R. E. Miller, Pathologist, U.S. Forest Service, Southeastern Area State and Private Forestry, Pineville, LA 71360. Plant Dis. 66:999-1000. Accepted for publication 27 February 1982. Copyright 1982 American Phytopathological Society. DOI: 10.1094/PD-66-999.

Rhabdocline needle cast of Douglas-fir Christmas trees was studied in Michigan in 19751976. Apothecia matured between 14 May and 4 June, with infected needles cast from 4 June until 17 July and later. Benomyl provided good disease control, ferbam and chlorothalonil were variable, whereas maneb and Bordeaux mixture were less effective. Fungicides were effective when applied by 4 June but were ineffective when applications were delayed until 26 June. Chlorothalonil application by mist blower was as effective as dip application. Disease control evaluations were equally reliable when made in the fall or spring.

Keyword(s): epidemiology, Pseudotsuga menziesii.