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Black Rot Lesions on Overwintered Canes of Euvitis Supply Conidia of Guignardia bidwellii for Primary Inoculum in Spring. C. M. Becker, Research Associate, Department of Plant Pathology, Cornell University, New York State Agricultural Experiment Station, Geneva 14456. R. C. Pearson. Plant Dis. 80:24-27. Accepted for publication 6 February 1995. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0024.

Black rot lesions, caused by Guignardia bidwellii, on overwintered canes of Euvitis grapevines released >8,000 conidia per lesion at budbreak in laboratory assays during 1990 and 1991; numbers declined during the growing season. Approximately 1,000 conidia per lesion were delected near harvest. During 1992, 250 and 900 conidia per lesion were detected from Aurore and Delaware canes, respectively, and no conidia were detected after 14 June, just before bloom. Significantly higher levels of black rot occurred on the foliage beneath individual, tagged lesions on overwintered canes than occurred on foliage growing beneath canes with no lesions. Significantly higher levels of black rot also occurred on vines suspended beneath bundles of 1-year-old canes with lesions, compared with vines without bundles. The level of black rot that developed beneath bundles of dead, 2-year-old canes with lesions was not significantly different from that beneath 1-year-old canes during a season with above average rainfall. Since lesions on dead, 2-year-old canes can be a source of inoculum, mechanically pruned grapevines, which are nonselectively pruned and retain debris in the trellis, may be at increased risk of black rot from this source of inoculum. Lesions on overwintered canes may be a more important inoculum source than mummies in hand-pruned vineyards, because conidia were released earlier, compared with mummies in the canopy, and the selective process of hand pruning usually removes mummies from the canopy. Lesions on 1 year-old canes are likely to be sources of inoculum in vineyards regardless of whether grapevines are pruned selectively by hand or nonselectively by machine.

Keyword(s): epidemiology, Vitis