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47

Meta-analysis of fungicide efficacy trials against Asian soybean rust in Brazil

Presenter: Harald Scherm(1)

Other authors and affiliations: Rock S. C. Christiano(1), Emerson M. Del Ponte(2), Paul D. Esker(3), Claudia V. Godoy(4). (1)University of Georgia, Athens, GA, U.S.A.; (2)Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil; (3)University of Wisconsin, Madison, WI, U.S.A.; (4)Embrapa Soja, Londrina, PR, Brazil

With the arrival of Asian soybean rust in the Western Hemisphere in 2001, field research to optimize chemical control of this important yield-limiting disease has proliferated. We present a meta-analytical synthesis of the results of 66 fungicide efficacy trials containing >800 entries (specific fungicidal treatments) conducted in Brazil from 2001/2002 to 2006/2007. Weighted median response ratios for disease severity (RS) and yield (RY) were 0.141 and 1.40, respectively, indicating that, on average, fungicide treatments reduced disease by 85.9% (range: 38.9 to 100%) and increased yield by 40.0% (range: 28.8 to 435%). Response ratios were dependent on disease pressure (expressed as disease severity of the untreated control), being worst under low disease pressure and best under medium (RS) or high (RY) disease pressure. Rank correlation analysis revealed a highly significant inverse relationship between RY and RS for low and high (but not medium) disease pressure. Based on a comparison of the empirical distribution functions between entries with one versus two seasonal fungicide applications, two applications significantly improved RS under low and medium disease pressure and RY for all three disease pressure classes. For trials that included multiple fungicide classes, pairwise differences in RS values between fungicide classes were calculated for each trial, and the median differences across trials were tested for deviation from zero. Based on this analysis, DMI fungicides performed significantly better than QoI fungicides. RS values of DMIs improved significantly in mixture with QoIs but not with benzimidazoles. Differences in performance among specific active ingredients will be discussed.

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