Severidade de ferrugem asiática e produtividade de soja irrigada e não irrigada submetida a diferentes manejos de fungicida

Abstract

In the cultivation of soybean (Glycine max (L.) Merrill) one of the factors that most burden the production system are fungicide applications to control Asian rust (Phakopsora pachyrhizi). The objective of this study was to evaluate the severity of asian rust, yield components and grain yield in soybean cultivated under irrigated and non-irrigated systems, submitted to different fungicide application management in lowland area of Rio Grande do Sul state. The experiment was conducted at the experimental area Universidade Federal do pampa - UNIPAMPA, Campus Itaqui, crop season 2018/2019. The experimental design used was a randomized complete block design (DBC), with a split plot and four replications. The main plot was the different water conditions (factor A) being the treatments irrigated (TI) and nonirrigated (TNI). Factor B was composed of three different fungicide application managements, totaling 24 experimental units. The fungicide managements were: control, without fungicide application (T1), fungicide applications following the phytosanitary alert model (T2), and scheduled applications at intervals informed by product leaflets registered for the crop (T3). Data on severity of disease incidence were collected from 20 plants per repetition, considering the trifoliate central leaflet of the lower third of each plant; yield component data were collected when the plant reached stage R8; and grain yield was estimated from an area of 5 m² of the useful area of the experimental plot, and corrected to 13% moisture in the grain. Data were subjected to analysis of variance (ANOVA) by the F test and comparison of means by the Scott Knott test at 5% probability of error. In the 2017/2018 agricultural year the incidence of Asian rust on the lower third of the plant in the R5 development stage did not differ statistically between the TI and TNI treatments. In the fungicide application management treatments, T1 presented the highest incidence value of the disease. In the agricultural year 2018/2019 the severity values in the IT were higher than the TNI. In TI T2 obtained the lowest severity value. In the two agricultural years, irrigation provided an increase in grain yield potential by increasing the number of vegetables per plant and mass of 1000 grains. In the 1st and 2nd crop year, the soybean grain yield values (kg / ha) obtained in the experiments indicate that all fungicide management treatments (T1, T2 and T3) in IT were superior to the same management as TNI. In the 2nd year for the fungicide application management values T2 was superior to the other treatments. Therefore, soybean productivity in lowlands has a most limiting factor of potential yield water stress due to lack of water. The use of irrigation allowed the highest yields found in the experiments. In the fungicide management employed to determine the timing of application, monitoring was more efficient, reducing the number of applications and maintaining productivity.