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30

The occurrence of soybean rust depends on crop phenologic stage?

Presenter: E. N. Moreira

All authors and affiliations: R. A. Rodrigues (1), E. N. MOREIRA (1), L. C. Costa (1), F. X. Ribeiro do Vale (1). (1) Universidade Federal De Viçosa, Viçosa, MG, Brazil

In the 2001 growing season, soybean rust, caused by Phakopsora pachyrhizi, caused serious damage to the soybean crop in Brazil. In the following seasons, it was claimed that the occurrence of soybean rust was somehow associated with plant growth stage. Therefore, this variable became a criterion for fungicide spraying for rust control. An experiment was carried out in the 2007 and 2008 growing seasons to test this hypothesis by using several soybean cultivars with three defined cycles sowed in three different seasons. Rust incidence and severity were evaluated on 10 plants taken randomly from each plot from the V4 to R5 growth stages. There was no significant difference between cultivars and growing seasons, which indicates that the occurrence of rust is not related to the plant growth stages. Soybean rust epidemics are more strongly associated with the amount of inoculum present in the field and the climatic conditions favorable to the disease progress.

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