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Control of Asian soybean rust (Phakopsora pachyrhizi) with Azoxystrobin-based fungicide products applied with or without spray adjuvants.

Presenter: Philip Brune, Syngenta Crop Protection, Greensboro NC
Coauthor(s): Gary Cloud, Syngenta Crop Protection, Greensboro NC; Allison Tally, Syngenta Crop Protection, Greensoboro NC; Martin Wiglesworth, Syngenta Crop Protection, Greensboro NC

Two trials were conducted in Brazil (2005 growing season) to study control of Asian soybean rust (Phakopsora pachyrhizi) with Azoxystrobin (AZO) based products applied with or without spray adjuvants. Treatments included three fungicides (Syngenta Crop Protection, Greensboro NC): AZO (Quadris? 2.08 SC), AZO + propiconazole (Quilt? 200 SE), and AZO + cyproconazole (Quadris? Xtra 2.34 SC). Two applications were made with or without a spray adjuvant at: 1) growth stage R2-R3, at <2% disease incidence; and 2) 21 days later. Disease severity was estimated over time by sampling 8 leaves each from the mid-canopy and the upper canopy. Fisher's protected LSD (p=0.05) was used to compare area under the disease progress curve values. Data also was collected on defoliation, yield (bushels per acre), and 1000-seed weight. The addition of 0.25% v/v non-ionic surfactant (Activator 90, Loveland Industries, Inc., Greeley CO) improved disease control only for AZO 113 g a.i./ha in the mid-canopy in one trial. In both trials, AZO 113 g a.i./ha + 1% v/v crop oil concentrate (Agri-dex?, Helena Chemical Co., Collierville, TN) improved disease control compared to AZO 113 g a.i./ha alone, and in one trial the addition of 1% crop oil concentrate also improved disease control of AZO 167 g a.i./ha and of AZO + propiconazole 200 g a.i./ha. At this location, the addition of 1% v/v crop oil concentrate to AZO 113 g a.i./ha decreased premature defoliation compared to AZO 113g a.i./ha alone, and resulted in higher yield and 1000-seed weight than AZO alone at either 113g or 167 g a.i./ha. These results show a significant benefit using crop oil concentrate at 1% v/v for improved performance of AZO-based fungicide products, except for the AZO + cyproconazole product.

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