Controle químico da ferrugem asiática e seu efeito na qualidade fisiológica de sementes de soja

Abstract

Brazil is the world's second largest producer and exporter of soybeans, showing a significant increase in its productivity over the last few harvests. Among the major factors limiting the achievement of high yields in soybeans are diseases. The Asian rust stands out for the rapid dissemination and defoliation of plants and under favorable environmental conditions, in three weeks, the rust can evolve from 5 to 90% of severity. The objective of this research was to determine the effects of different numbers and times of applications and active ingredients of fungicides to control Asian rust on the physiological quality of soybean seeds. The experiment was conducted in field conditions during the 2005/2006 crop year, at Jotabasso Farm, located in the municipality of Ponta Porã, southwest of the state of Mato Grosso do Sul, using soybean cultivars CD 202 and BRS 239, Sown in plots of 10 m wide and of length, being only 24 m² considered useful area. The treatments consisted in the application of fungicides in different phases, as follows: A1 (control, without application), A2 (methyl thiophanate + flutriafol in R2), A3 (methyl thiophanate + flutriafol in R2 and R4), A4 (methyl thiophanate + flutriafol In R4); B1 (Pyraclostrobin + epoxiconazole in R2), B3 (Pyraclostrobin + epoxiconazole in R2 and R4), B4 (Pyraclostrobin + epoxiconazole in R4); And C1 (control, no application), C2 (Tebuconazole in R2), C3 (Tebuconazole in R2 and R4), C4 (Tebuconazole in R4). In the useful area of all the plots were 700 flowers marked with the aid of sturdy strands, at the beginning of full flowering of the cultivars. The harvest of the marked pods and their trail were done manually. The drying process of the material was naturally performed in the shade. The determination of the degree of seed moisture of the seeds was carried out by the universal equipment. After the analysis of the physiological quality of the harvested seeds, performed in LSA-FAEM / UFPel. Two periods of analysis were conducted, the first one performed immediately after harvest and the second after six months of storage, in a cold room at a temperature of 15 ºC (± 2 ºC) and relative humidity (RH) between 40 and 50%. The set of tests performed consisted of: weight of one thousand seeds, germination test, first germination count, seedling vigor classification, seedling length, accelerated aging and emergence in the field. The results obtained allow us to conclude that the application of fungicide in the control of asian rust favors the increase in the mass of one thousand seeds, in applications made in R2 + R4 and in R4, and does not cause detrimental effect on the physiological quality, aerial part and root system of seeds of soybean.