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52

Evaluation of fungicides and fungicide timing for the control of Phakopsora pachyrhizi in Paraguay and Zimbabwe

Presenter: T. A. Mueller

All authors and affiliations: T. A. MUELLER (1), W. Morel (2), C. Levy (3), M. R. Miles (4), and G. L. Hartman (1,4). (1) Department of Crop Sciences, National Soybean Research Center, University of Illinois, Urbana, IL 61801; (2) Centro Regional de Investigación Agrícola, Ministerio de Agricultura y Ganadería, Capitán Miranda, Itapúa, Paraguay; (3) Commercial Farmers Union of Zimbabwe, Harare, Zimbabwe; and (4) USDA-ARS, National Soybean Research Center, University of Illinois, Urbana, IL 61801

Timing of fungicide applications is a critical component in managing soybean rust and, if used effectively, may reduce the number of applications needed for economic benefit. The objectives of these experiments were to evaluate the effects of different timings of fungicide applications on soybean rust severity and yields. Trials were conducted in three locations in Paraguay in growers’ fields (Bella Vista, Pirapo, and Capitán Meza) and in Harare, Zimbabwe, at the Rattray Arnold Research Station. Varieties of soybean were representative of the region they were planted in. Treatments in each field included applications with triazole (Folicur), strobilurin (Headline), or triazole-strobilurin combinations (Quilt or Headline + Folicur) at either (i) growth stage (GS) R1, (ii) GS R3, (iii) GS R5, (iv) GS R1 and R3, (v) GS R3 and R5, (vi) GS R1, R3, and R5, or (vii) not sprayed. For all locations, the nontreated control had higher soybean rust severity and lower yield than most of the treatments with fungicides. In Zimbabwe, the yields for 15 of the 23 treatments were significantly greater than the nontreated control. In Paraguay, Bella Vista had 6, Pirapo had 19, and Capitán Meza had 17 of 23 treatments that had significantly greater yields than the nontreated control. In general, when fungicides were applied, soybean rust was less severe and the yields were higher with a tendency to be greater as the number of fungicides applications increased. The fungicides were applied with a backpack sprayer with TeeJet XR11002 tips at 40 psi in Paraguay and with Lurmark® F110/1.6/3 flood-jet nozzles at 44 psi in Zimbabwe.

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