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Biological Control of Grape Powdery Mildew Using Tydeid Mites 1998

Project Leaders: Greg English-Loeb, Andrew Norton, David Gadoury, Robert Seem, Wayne Wilcox

Objectives:

1. Assess the relationship between grape species/cultivar, tydeid mite (O. lambi) abundance, and incidence and severity of powdery mildew under a common vineyard setting.

2. Examine the relationship between tydeid mite density and development of grape powdery mildew.

Results:

In the first season over 700 rooted grapevine cuttings were successfully established at the Geneva Experiment Station. Orthotydeus lambi became established on all grape species and genotypes, with the maximum density per leaf of 26 found on the interspecific hybrid ‘Seyval’ and the lowest density per leaf of 3 found on Chardonnay. There were no major differences in O. lambi numbers as a function of grape species. Mildew levels were only assessed for a subset of vines at the end of the season by estimating density of cleistothecia from a small sample of leaves. Vines that received O. lambi and no fungicide had slightly fewer cleistothecia, overall, than vines without mites and fungicide (6.7 vs. 8.3), although the difference was not significant.