Skip to main content
ARS Home » Pacific West Area » Corvallis, Oregon » Forage Seed and Cereal Research Unit » Research » Publications at this Location » Publication #311057

Title: Meta-analysis reveals a critical period for management of powdery mildew on Hop cones

item NELSON, M - Washington State University
item Gent, David - Dave
item GROVE, G - Washington State University

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2014
Publication Date: 6/3/2015
Citation: Nelson, M.E., Gent, D.H., Grove, G.G. 2015. Meta-analysis reveals a critical period for management of powdery mildew on Hop cones. Plant Disease. 99:632-640.

Interpretive Summary: Meta-analysis is an approach to quantitatively summarize and synthesize research results from multiple experiments. In this study, we applied meta-analysis to synthesize data from 28 field trials conducted over a 12-year period investigating various fungicide and biological control treatments for management of hop powdery mildew. The data available allowed analysis of individual plot-level observations, which is a unique approach in meta-analysis in plant disease research. By doing this, we found differences among fungicides in their effectiveness for controlling powdery mildew on both leaves and cones. Of particular importance, fungicides in one specific group were found to be especially effective when applied during a brief period of the season corresponding to the early stages of cone development. Collectively, these findings suggest a highly important period for disease development and control where disease management efforts should be especially be focused to mitigate crop damage.

Technical Abstract: Results of 28 field trials conducted over a 12-year period investigating management of hop powdery mildew caused by Podosphaera macularis were quantitatively summarized by meta-analysis to compare product efficacy and use patterns by mode of action as defined by Fungicide Resistance Action Committee (FRAC) groups. Availability of original observations enabled individual participant data meta-analysis. Differences in control of powdery mildew on leaves and cones were apparent among fungicide FRAC groups when individual products were evaluated over the course of a growing season. FRAC groups 13, 3, and U13 provided the most efficacious control of powdery mildew on leaves. Percent disease control on cones was influenced by mid-season foliar disease and fungicide mode-of-action. FRAC 13 provided significantly better disease control on cones than all other groups except U13 and premixes of 7 with 11. In contrast, disease control on leaves and cones was similar when a rotational program of fungicides was used, independent of the modes-of-action used in the rotation or which fungicide was applied as the initial application of the season. Disease control on cones was improved from 28 to 49%, on average, when the fungicide quinoxyfen (FRAC 13) was applied at least once during the early stages of cone development, defined in this analysis as 20 July to 10 August, as compared to all other treatments. Efficacy of disease control on cones by quinoxyfen was moderated by and interacted with the incidence of leaves with powdery mildew. Disease control on cones was further improved if two applications of quinoxyfen were made during this period. Collectively, these findings suggest an important epidemiological event during juvenile stages of cone development providing evidence that disease management strategies should especially be focused during this stage of development, independent of what actual management strategy is employed.