An overview of chemical control of late season diseases of soybean in Tucumán Argentina

PLOPER, L.D.; JALDO, H; GÁLVEZ, M R; GONZÁLEZ, V; ZAMORANO, M A; DEVANI, M

Foz do Iguassú

Conferencia; VII World Soybean Research Conference (VII WSRC).; 2004

Embrapa SOJA y WSRC Continuing Committee

Soybean diseases in Tucumán and other provinces of northwestern Argentina (NWA) have increased in importance since the early 1990s.  The late season disease complex, a combination of various diseases that affect foliage, stems, pods, and seeds during the mid to late reproductive growth stages, has been shown to cause significant yield losses, especially under conditions that favor the development of these diseases.  The most common late season diseases in NWA are brown spot (Septoria glycines), leaf blight (Cercospora kikuchii), downy mildew (Peronospora manshurica), frogeye leaf spot (Cercospora sojina), target spot (Corynespora cassiicola), pod and stem blight (Diaporthe phaseolorum var. sojae), Phomopsis seed decay (Phomopsis spp.), and anthracnose (Colletotrichum spp.).  Application of foliar fungicides is considered the most effective way of managing these diseases under the current cropping conditions in NWA (soybean monoculture and no-till systems).  Extensive field evaluations of foliar fungicides have been carried out in Tucumán since the 1998/99 growing season.  This report summarizes yield data from 18 experiments conducted in the past 3 seasons (2000/01, 2001/02, and 2002/03), in which different fungicides, rates, and application moments were compared.  Experiments were conducted at the EEAOC Monte Redondo Substation in San Agustín, Tucumán, in fields previously cropped to soybean. Treatments were arranged in randomized complete blocks with four replications per test. Plots consisted of four, 6-m rows, spaced 0.5 m apart.  Disease and yield data were obtained from the center two rows. Fungicides were applied with a CO2 backpack sprayer. A total of 227 treatments were evaluated. The fungicides carbendazim, benomyl, thiophanate-methyl, epoxiconazole + carbendazim, fenbuconazole, miclobutanil, tebuconazole, difenoconazole + propiconazole, azoxystrobin, trifloxystrobin + cyproconazole, and pyraclostrobin were compared at different rates and application moments.  Out of a total of 227 fungicide treatments, only 68 (30 %) showed significant yield differences with respect to the untreated control.  Of those 68 cases, 21 (31%) were benzimidazoles, 17 (25%) triazoles, and 30 (44%) strobilurins.  Throughout the 18 experiments, in only 42 cases a paired comparison between R3 and R5 applications was possible.   Fifty-five of those treatments were not significantly different from the untreated controls, while 13 and 16 treatments differed significantly from the untreated control when applied at R3 or R5, respectively.  In 11 of those 42 cases, there were significant yield differences between application stages, 7 in favor of the R3 and 4 in favor of the R5 application. In the 68 cases that differed significantly from the untreated control, a mean yield increase of 483 kg/ha was obtained as a response to the fungicide application.