Submitted to: USDA Website Risk Assessment
Publication Type: Other
Publication Acceptance Date: 12/10/2004
Publication Date: 12/10/2004
Citation: Miles, M.R., Morel, W., Hartman, G.L. 2004. Summary of the USDA fungicide efficacy trials to control soybean rust in Paraguay 2002-2003. USDA Website Risk Assessment.
Technical Abstract: The Asian soybean rust, caused by Phakopsora pachyrhizi, is one of the most devastating diseases of soybean world wide, causing yield losses of up to 80 % in experimental plots. With the spread into South America the pathogen has become a threat to soybean production in the continental U.S. Fungicides, although not commonly used on soybean in the U.S., will be the primary method of control. The objectives of these trials were to evaluate soybean rust control and yield benefits from fungicides that are or could be registered for use in the continental U.S. Fungicide efficacy trials were located in the Parana River basin of southern Paraguay during the 20022003 growing season. A total of 20 fungicide treatments were evaluated in plots that received either two or three fungicide applications. A total of five locations were included in the trial, data from three locations were summarized. All compounds controlled soybean rust when compared to the untreated control; disease severity was less in all the plots treated with fungicides. Seed weights and yield varied but were inconsistent to draw conclusions about the effectiveness of fungicides in terms of preventing yield losses since in general disease severity was not that great. To make these kinds of trials more effective, experimental locations need to be placed where they can irrigated and inoculated. If natural inoculation and rainfall are relied upon to provide disease severities sufficient to evaluate fungicides then the number of locations and years of testing will need to be increased.