Submitted to: Plant Disease Management Reports
Publication Type: Other
Publication Acceptance Date: 9/19/2007
Publication Date: 10/7/2007
Citation: Mueller, T.A., Miles, M.R., Hartman, G.L., Morel, W. 2007. Evaluations of fungicides and fungicide timing for the control of soybean rust at Pirapo, Paraguay, 2005-2006. Plant Disease Management Reports.1:FC063 Interpretive Summary:
Technical Abstract: About 8500 soybean seeds were planted at Bella Vista, Paraguay on 7 Feb 2005 in four row plots, 24 ft long, with 18-in row spacing and two rows of border. The experimental design was a randomized complete block with four replicates. Treatments consisted of Headline 2.09EC, Folicur 3.6F, Quilt 1.67SC applied at growth stage R1, R3, R5 with either one, two or three applications; Folicur 3.6F and Headline 2.09EC together or in sequence. Fungicides were applied at 52, 72, and 92 days after planting (DAP) at 15 gal water per acre with a hand-operated backpack sprayer fitted with a pressure regulator set to 40 psi and equipped with TeeJet 8002 flat fan nozzles spaced 20-in. apart. Soybean plants were rated for soybean rust 63, 85, 92, and 98 DAP in the lower, middle, and upper canopy. Ratings from these dates were used to calculate the area under disease progress curve (AUDPC). The rating scale used was a 0 to 9 severity scale where a rating of “0” had no rust and “9” had severe symptoms. The average of the lower, middle, and upper canopy was used for analysis. The middle two rows of each plot were harvested at 121 DAP and the yield was adjusted to 13 percent moisture. Soybean rust was first observed 62 DAP, so only the first fungicide applications was applied as a protectant and the second and third applications were applied curatively. There were significant differences among treatments for soybean rust severity, seed weight, and yield. All treatments had significantly less soybean rust than the untreated control, 19 of the 23 treatments had higher yield than the untreated control, and 19 of the 23 treatments had greater seed weight compared to the untreated control. No phytotoxicity was observed for any treatments.