Soybean rust incidence and control in Northwestern Argentina

PLOPER, L. D.

Londrina, Paraná, Brasil

Workshop; South American Workshop on Soybean Rust; 2006

JIRCAS y Embrapa Soja

Asian soybean rust, caused by Phakopsora pachyrhizi, is regarded as one of the most destructive diseases of soybean [Glycine max (L.) Merr.]. In Argentina it was detected first in the province of Misiones, in northeastern Argentina near Paraguay and Brazil during the 2001/02 growing season. The following season, it also was found in the neighboring province of Corrientes. However, it did not reach major soybean production areas in northwestern Argentina (NWA), which includes the provinces of Tucumán, Jujuy, Catamarca, and Santiago del Estero, until the end of the 2003/04 season. Affected crops were mostly in growth stages R7 to R8 except for a few fields that had been planted late and were in a late R5 stage. Molecular studies confirmed that only P. pachyrhizi was present in the soybean samples. In the 2004/05 season, the first report of soybean rust in NWA was in Tartagal, Salta during the second week of March 2005. In Tucumán, it was detected on 30 March. As in the previous season, little damage occurred as the disease appeared during the late reproductive stages. In the 2005/06 season, soybean rust in NWA was observed first on 18 February 2006 in the department of Anta, Salta. In Tucumán, the detection was on 28 February, that is, 30 days earlier than in the 2004/05 season and 52 days earlier than in the 2003/04 season. The highest incidence of the disease was observed in the northeastern part of Tucumán (department of Burruyacú), western Santiago del Estero (Jiménez and Pellegrini), and northern Salta (San Martín).In this season, the disease appeared earlier than in the previous years and reached severity levels not observed in previous years prior to physiological maturity. Epidemiological studies conducted in Tucumán and neighboring provinces revealed important differences in disease progress among seasons, locations, and cultivars. One of the three cultivars evaluated showed a delay on the onset of the epidemic and a reduced rate of progress even under environmental conditions favorable for the disease. Fungicide efficacy studies indicated that several products were effective in controlling soybean rust. The best levels of control were obtained with triazole/strobilurin mixtures, followed by a cyproconazole/difenoconazole mix, flutriafol, and a cyproconazole/propiconazole mix.