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United States Department of Agriculture

Agricultural Research Service

Research Project: SOYBEAN DISEASE AND PEST MANAGEMENT

Location: Soybean/maize Germplasm, Pathology, and Genetics Research

Title: Effect of Fungicide and Time of Application on Soybean Rust Severity and Yield

Authors
item Mueller, T - UNIV. OF ILLINOIS
item Morel, W - CRIA, PARAGUAY
item Marois, J - UNIV. OF FLORIDA
item Wright, D - UNIV. OF FLORIDA
item Kemerait, R - UNIV. OF GEORGIA
item Miles, Monte
item Levy, C - COM/FARMERSUNION,ZIMBABWE
item Hartman, Glen

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 13, 2008
Publication Date: March 25, 2009
Repository URL: http://hdl.handle.net/10113/30672
Citation: Mueller, T.A., Morel, W., Marois, J.J., Wright, D.L., Kemerait, R.C., Miles, M.R., Levy, C., Hartman, G.L. 2009. Effect of Fungicide and Time of Application on Soybean Rust Severity and Yield. Plant Disease. 93(3):243-248.

Interpretive Summary: Soybean rust is a devastating foliar disease of soybean. Soybean yield losses up to 80% in experimental trials have been reported in Asia. Currently there are no commercial cultivars in the U.S. that are resistant to soybean rust making it feasible that millions of soybean hectares may be sprayed with fungicides if soybean rust becomes widespread. Field trials were completed in Paraguay (four locations), United States (two locations), and Zimbabwe (one location) to determine the effect of fungicide timing on soybean rust severity and soybean yield. Mean yields from plants in fungicide plots ranged from 16 to 114% greater than yields in non-fungicide control plots in four locations in Paraguay, 31% greater in Zimbabwe, and 12 to 55% greater in two locations in the U.S. In all locations, rust severity was negatively correlated to yield. The effectiveness of any given fungicide treatment was often dependent on when rust was first detected and the intensity of its development. This information is important for soybean producers, pathologists and others interested in managing soybean rust.

Technical Abstract: Soybean rust, caused by Phakopsora pachyrhizi, is a devastating foliar disease of soybean that may cause significant yield losses. One effective means of managing soybean rust is by well-timed fungicide applications. Field trials were completed in Paraguay (four locations), United States (two locations), and Zimbabwe (one location) to determine the effect of fungicide timing on soybean rust severity and soybean yield. Treatments at each location included applications with a triazole (tebuconazole), a QoI fungicide (pyraclostrobin), or a triazole-QoI fungicide combination (azoxystrobin + propiconazole) at either (i) growth stage (GS) R1, (ii) GS R3, (iii) GS R5, (iv) GS R1/R3, (v) GS R3/R5, or (vi) GS R1/R3/R5. Mean yields from plants in fungicide plots ranged from 16 to 114% greater than yields in non-fungicide control plots in four locations in Paraguay, 31% greater in Zimbabwe, and 12 to 55% greater in two locations in the U.S. In all locations, rust severity measured as area under the disease progress curve (AUDPC), was negatively correlated (r = -0.3, P < 0.0001) to yield. When soybean rust was first observed before GS R3 (two locations in Paraguay), the plants in plots sprayed with fungicide at GS R1 had the lowest AUPDC values and highest yields. When soybean rust was first observed after GS R3, plants with fungicide treatments at GS R3 and/or GS R5 had the lowest AUDPC value and highest yield with few exceptions. Some individual fungicide treatments did not reduce rust severity or increase yields compared to plants that were not treated with a fungicide. The effectiveness of any given fungicide treatment was often dependent on when rust was first detected and the intensity of its development.

Last Modified: 7/31/2014
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