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Dispersal of Aeciospores of Peridermium harknessii in Central Nebraska. Glenn W. Peterson, Plant Pathologist, Rocky Mountain Forest and Range Experiment Station, Forest Service, USDA, Lincoln, Nebraska 68503; Phytopathology 63:170-172. Accepted for publication 20 August 1972. DOI: 10.1094/Phyto-63-170.

Western gall rust, caused by Peridermium harknessii, is prevalent in pine plantations on the Nebraska National Forest near Halsey, Nebr. As high as 4% of pine seedlings and transplants in the adjacent Bessey Nursery have been infected by this rust. Automatic volumetric spore traps and weather recording equipment were installed in and adjacent to the nursery to determine when and under what conditions aeciospores are dispersed. On rainless days, there was diurnal periodicity in the number of spores trapped. The number of spores increased sharply in the morning (0700 hr) as air temperature increased and relative humidity decreased. Numbers of spores reached a maximum about 1100 hr, and decreased sharply about 1300 hr. This periodicity was interrupted on days with rain. Aeciospores were dispersed as early as 8 May; dispersal was essentially completed by the end of June. During the 2 years of trapping, dispersal was over 80% completed by the end of May.