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 Bella Vista, Paraguay, 2005-2006. Plant Disease Management Reports.1:FC04
Technical Abstract: About 8000 soybean seeds were planted at Bella Vista, Paraguay on 12 Nov 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 design with four replications. 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 plus Folicur 3.6F and Headline 2.09EC together or in sequence. Fungicides were applied at 69, 88, and 102 days after planting (DAP) at 15 gallons 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 inches apart. Soybean plants were rated for soybean rust 102, 123, and 137 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 151 DAP and the yield was adjusted to 13 percent moisture. Soybean rust was first observed 102 DAP, so the first two fungicide applications were applied as a protectant and the third application was applied curatively. The weather was dry early in the growing season, but moisture increased later as well as the soybean rust. The disease developed late, but had high disease pressure in the late growth stages. There were significant differences among treatments for soybean rust severity (both final and overall), seed weight, and yield. All treatments had significantly less soybean rust (both final and overall) and 23 of the 26 treatments had greater seed weight than the untreated control, but only 6 of the 23 treatments had higher yield than the untreated control. No phytotoxicity was observed for any treatments.