Outbreak of Tranzschelia discolor Causing Almond Rust Disease in Northern California. J. M. Ogawa, Department of Plant Pathology, University of California, Davis 95616. H. A. Bolkan, and W. H. Krueger, Department of Plant Pathology, University of California, Davis 95616, and Glenn County Cooperative Extension Service, Orland, CA 95963. Plant Disease 68:351, 1984. Accepted for publication 6 January 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/PD-68-351g.
Tranzschelia discolor Fuckel, last observed in California in 1979 in Glenn County, reappeared in June 1983 in the same county and caused early defoliation on almond (Prunus dulcis (Mill.) D. A. Webb) cultivars Nonpareil, Carmel, and Ne Plus Ultra. On 31 October 1983, severe rust infections were found on leaves of the cultivars Mission, Price, Peerless, Merced, and Harvey in the area of Hamilton City and Ord Bend, Glenn County; orchards in nearby Colusa, Butte, and Yuba counties had only scattered infections. No twig infections or differences in host susceptibility were observed. Severe rust infections were observed on French prunes throughout the Sacramento Valley, but few rust infections were seen on apricots, peaches, and suckers of Marianna 2624 rootstock.