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Association of Spring Pruning Practices with Severity of Powdery Mildew and Downy Mildew on Hop

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dc.creator Gent, David H.
dc.creator Nelson, Mark E.
dc.creator Grove, Gary G.
dc.creator Mahaffee, Walter F.
dc.creator Turechek, William W.
dc.creator Woods, Joanna L.
dc.date.accessioned 2012-11-20T19:53:51Z
dc.date.available 2012-11-20T19:53:51Z
dc.date.issued 2012-09
dc.identifier.citation Gent, D. H., Nelson, M. E., Grove, G. G., Mahaffee, W. F., Turechek, W. W., and Woods, J. L. 2012. Association of spring pruning practices with severity of powdery mildew and downy mildew on hop. Plant Disease. 96:1343-1351. en_US
dc.identifier.uri http://hdl.handle.net/1957/35126
dc.description This is the publisher’s final pdf. The published article is copyrighted by the American Phytopathological Society and can be found at: http://apsjournals.apsnet.org/loi/pdis. To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. en_US
dc.description.abstract Downy mildew (caused by Pseudoperonospora humuli) and powdery mildew (caused by Podosphaera macularis) are important diseases of hop in the Pacific Northwest United States, and cultural practices may affect the severity of both diseases. The association of spring pruning quality and timing with severity of downy mildew and powdery mildew was assessed through analysis of survey data collected from commercial hop yards in Oregon and Washington. Among 149 hop yards surveyed, the most common pruning method was chemical desiccation (48% of yards), mechanical pruning (23%), or a combination of these practices (15%). The quality of pruning was assessed using a three-category ordinal scale (“excellent”, “moderate”, or “poor”) based on the amount of foliage remaining on plants following pruning. Excellent pruning quality was attained more often in yards pruned twice (74.6 to 82.1% of yards) versus once (33.8% of yards), independent of pruning method. Seasonal severity of downy mildew in Oregon increased approximately twofold with reduction in pruning quality from excellent to moderate to poor. Pruning quality was not significantly related to levels of powdery mildew on leaves or cones in Oregon. Under more severe disease pressure in Washington, however, seasonal severity of powdery mildew on leaves and the incidence of cones with powdery mildew were significantly greater in yards that had poor pruning compared with excellent pruning. Moreover, yards that had excellent pruning quality received, on average, 1.1 to 1.5 fewer fungicide applications per season for downy mildew or powdery mildew compared with yards that had moderate or poor pruning quality. This savings was associated with delayed initiation of the first application by 7.5 to 14.2 days in yards with excellent pruning quality. Replicated experiments in commercial yards in Oregon quantified the effect of delaying pruning timing 5 to 21 days compared with growers' standard practices on the diseases and yield. Downy mildew suppression by delayed pruning was dependent on cultivar and year of sampling, being significantly reduced fivefold only in ‘Willamette’ in 2007. Severity of powdery mildew and cone yield was similar between plots that received the delayed or standard pruning timing treatments. Collectively, these studies emphasize that early spring sanitation measures are associated with reduced primary inoculum and are critically important for managing both downy mildew and powdery mildew. A savings of at least one fungicide application per year appears achievable when spring pruning is conducted thoroughly and slightly delayed compared with growers' current practices. en_US
dc.description.sponsorship Funding for these studies was provided by the Agricultural Research Foundation, Hop Research Council, Oregon Hop Commission, Oregon State University, Washington Hop Commission, Washington State University, and USDA-ARS CRIS Projects 303-5358-22000-030-00D and 5358-21000-035-00. en_US
dc.language.iso en_US en_US
dc.publisher The American Phytopathological Society en_US
dc.relation.ispartofseries Plant Disease en_US
dc.relation.ispartofseries Vol. 96 no. 9 en_US
dc.title Association of Spring Pruning Practices with Severity of Powdery Mildew and Downy Mildew on Hop en_US
dc.type Article en_US
dc.description.peerreview yes en_US
dc.identifier.doi 10.1094/PDIS-01-12-0084-RE

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