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Winter Air-Blast Sprayer Applications of Benomyl for Reduction of Eutypa Dieback Disease Incidence in a Concord Grape Vineyard in Michigan. D. C. RAMSDELL, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824. Plant Dis. 79:399-402. Accepted for publication 16 January 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-0399.

The efficacy of closely managed pruning and winter air-blast spraying of mature Concord grapevines with benomyl or benomyl plus oil for control of Eutypa dieback disease caused by Eutypa lata was evaluated in a commercial-scale test plot. Three pruning and spraying timings (early winter, mid-winter, or late winter early spring) were tested. Blocks of vines were sprayed as soon after pruning as possible prior to any rain, and when the ambient temperature was above 0 C. An air-blast sprayer was calibrated to deliver 281 h/ha of spray (30 gallons/ acre). Benomyl SOW or benomyl 50DF was applied at 1.12 kg 814/ha (1 lb a.i./acre) with or without Volck Supreme oil at 1% (v/v). A pruned but unsprayed control was included in each pruning-spraying timing block. Pruning-spraying was initiated in December 1984. Each pruning-spraying block received annual superimposed treatments for 5 yr. Symptom counts were made annually from May 1988 through 1992. Rainfall amount and duration and periods of temperature below freezing were recorded relative to pruning and spraying for a period of at least 30 days after sprays were applied. The early winter timing block did not provide useful data, due to low disease incidence. The mid-winter pruning-benomyl-sprayed treatment (early January to mid-February) resulted in a significant 5-yr cumulative reduction of 48.5% of vines with Eutypa dieback compared with the unsprayed, pruned control vines. The late winter-early spring pruning-spraying treatment resulted in a significant cumulative 5-yr reduction of vines with Eutypa dieback resulting from benomyl sprays (34% reduction) and benomyl plus oil sprays (21% reduction) compared with pruned and unsprayed control vines