Distribution of Tomato Ringspot Virus in Dandelion in Pennsylvania. C. A. Powell, Pennsylvania Department of Agriculture, Harrisburg 17110. W. L. Mountain, Pennsylvania Department of Agriculture, Harrisburg 17110; T. Dick, Department of Plant Pathology, Pennsylvania State University, Fruit Research Laboratory, Biglerville 17307-0309; L. B. Forer, M. A. Derr, and L. D. Lathrop, Pennsylvania Department of Agriculture, Harrisburg 17110; and R. F. Stouffer, Department of Plant Pathology, Pennsylvania State University, Fruit Research Laboratory, Biglerville 17307-0309. Plant Dis. 68:796-798. Accepted for publication 16 March 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/PD-68-796.

Population densities of Xiphinema spp. (X. americanum and X. rivesi) and common dandelion (Taraxicum officinale) and relative infection of dandelion with tomato ringspot virus (TmRSV) were determined in peach orchards with TmRSV- induced disease (Prunus stem pitting [PSP]), peach orchards without PSP, and nonorchards in eight geographic regions of Pennsylvania representing both intensive and nonintensive peach production areas. There were no significant differences (P = 0.05) in Xiphinema or dandelion density among types of sites or geographic regions. The percentage of dandelion infection with TmRSV was significantly higher (P = 0.05) in orchards with PSP (29%) than in either orchards without PSP (7%) or nonorchards (5%). Prevalence of TmRSV in dandelion was also greater (P = 0.05) in intensive peach production areas (21%) than in nonintensive peach production areas (7%). There were two geographic regions in which no TmRSV-infected dandelion was detected. These data indicate that in Pennsylvania, TmRSV is not yet endemic in dandelion and that the presence of TmRSV, not the nematode vector or dandelion, is the limiting component of the PSP disease. Results support the hypothesis that TmRSV is initially introduced in an orchard via either infected nursery stock or dandelion seed and subsequently becomes established in dandelion and other weeds over a period of years.