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Eutypa Dieback of Grapevine: Seasonal Differences in Infection and Duration of Susceptibility of Pruning Wounds. C. H. Petzoldt, Graduate research assistant, Department of Plant Pathology, University of California, Davis 95616; W. J. Moller(2), and M. A. Sall(3). (2)(3)Extension plant pathologist, and assistant professor of plant pathology, respectively, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 71:540-543. Accepted for publication 30 October 1980. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-540.

Grapevines growing in Davis, CA, were pruned at three different times (19 December 1978, 6 February 1979, and 12 March 1979) and wounds on 1-yr-old wood were inoculated with 0, 100, or 1 103 ascospores of Eutypa armeniacae at weekly intervals after pruning. The wounds were most susceptible to infection in December and least susceptible in March. Wounds were susceptible for a longer period of time after pruning in December than after pruning in March. Wound size and relative position of a wound on a vine did not have a significant effect on infection after inoculation. In most cases, more infections resulted when wounds were inoculated with 1 103 ascospores than when 100 ascospores were used. These findings suggest that pruning in late February or early March may be desirable to avoid Eutypa dieback in California regions where the disease is most prevalent.

Additional keywords: apricot dieback, dying arm of grapevine.