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Spatial Patterns of Grapevines with Eutypa Dieback in Vineyards with or without Perithecia. G. P. Munkvold, Assistant professor, Department of Plant Pathology, Iowa State University, Ames 50011; J. A. Duthie(2), J. J. Marois(3). (2)Plant Pathologist, Wes Watkins Agricultural Research Center, Oklahoma State University, Lane 74555; (3)professor, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 83:1440-1448. Accepted for publication 1 September 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/Phyto-83-1440.

Eight vineyards in northern and central California were surveyed during three consecutive years, 19891991, and the presence or absence of Eutypa dieback symptoms was recorded for each vine in contiguous blocks of 1,2503,150 vines. The vineyards were located in areas with different levels of mean annual rainfall; some vineyards contained inoculum sources (perithecia) of Eutypa lata; others did not. The spatial patterns of infected vines were examined by ordinary runs, two-dimensional distance class, spatial autocorrelation, and geostatistical analyses. Disease incidence ranged from 3.4% in 1989 to 81.5% in 1991. During the study, disease incidence more than doubled in five of the vineyards. Vineyards with perithecia had higher disease incidence. A disease gradient or edge effect was detected in two vineyards that did not contain inoculum sources; one of these was found to be adjacent to a vineyard with E. lata perithecia. The different analyses consistently described the relative randomness of the patterns of diseased vines among the vineyards. Those vineyards that contained perithecia had a higher proportion of vineyard rows with nonrandom disease patterns according to runs analysis. Two-dimensional distance class analysis showed that vineyards with perithecia contained clusters of diseased vines or other nonrandom patterns. Vineyards with perithecia also consistently had more significant spatial autocorrelation coefficients and semivariograms that indicated spatial dependence at distances up to 25 m. A nonrandom pattern was consistently found in one vineyard that was not near any known inoculum source. Three other vineyards with no known inoculum sources nearby were consistently considered to have random patterns, according to the spatial pattern analyses. In these vineyards, there was no evidence that would indicate disease spread by means other than airborne ascospores from distant sources.

Additional keywords: deadarm, epidemiology, Eutypa armeniacae.