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44

Production components of soybean in relation to fungicide spraying to control the Asian rust

Presenter: Guy Mitsuyuki Tsumanuma(1)

Other authors and affiliations: Antonio Luiz Fancelli(1), Marco Antonio Tavares Rodrigues(2), Edson Begliomini(2), Andre Venturoso Furlanis(1), Rafael Bigoto(1), Camila Heuser(1). (1)ESALQ/USP, Crop Production, Piracicaba, Sao Paulo 13418-900, Brazil; (2)BASF-SA, Sao Paulo, Brazil

Asian rust (Phakopsora pachyrhizi Syd.) has been causing significant production losses in all the regions that produce soybean in Brazil. This study aimed at determining which of the production components were responsible for a decrease in productivity. Cultivar “Conquista” was sown off-season (“safrinha”) on 10/01/06. The fungicides were sprayed on the aerial part of the plants by the means of a CO2-propelled backpack sprayer equipped with twin jet nozzles (Micron 110DB2), and 150 liters ha–1 being the spray volume. Sprayings were carried out at the development stages V4, R2, and R4. The experimental design was randomized blocks with four replications, having a plot size of 2 × 10 m. The production components of the crop were evaluated right after harvesting, and the means were compared with the Tukey test at 5% of probability. The following parameters were affected: number of pods per plant, number of seeds per plant, thousand grain weight, and productivity. The treatment with three sprayings of F500® showed the highest number of pods and seeds per plant, thus enabling a higher productivity. It is important to note that spraying F500® only at V4 showed no difference from the control since spraying at this phenological stage does not leave enough residual to control the disease at more advanced stages of the crop development. Both the treatments with two (R2 and R4) and three sprayings of F500® showed significant differences from the other treatments in the thousand grain weight.

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