Análise técnica e cononômica do controle químico da ferrugem da folha da aveia

Abstract

Crown rust is the main disease of oats in Southern Brazil. In susceptible cultivars the disease may reduce grain yield by 100%. Fungicides are frequently used to control rust, at one or two sprays along crop season. Although most oat cultivars are susceptible to rust, their reaction to disease and their response to the chemical control may vary. Also, rates and spray volumes used to deliver fungicides may affect control efficacy. Therefore optimization of rust control should consider all these variables. In 2002 and 2003, field trials were carried out at the FAMV/UPF to evaluate, both technically and economically, the chemical control of crown rust. These trials included different cultivars UPF 18, UPF 19, UPFA 20, and UPFA 22, sprayed with two fungicides, tebuconazol (Folicur) or epoxiconazol + pyraclostrobin (Opera), at different plant growth stages (elongation, booting, flowering, and elongation + flowering). The fungicides were delivered at 150 L.ha-1 by flat jet nozzles (DG 110015). Other experiments with the cultivar UPFA 20 included different rates of fungicide (40, 60, 80, and 100 % of the recommended rate), and two spray volumes (100 and 200 L.ha-1). In all trials disease severity was assessed five to six times along the crop season and integrated as area under the disease progress curve (AACPF). In both crop seasons the cultivar UPF 19 showed the highest AACPF and the lowest grain yield. UPFA 22 yielded more than UPFA 20 in 2002 but less in 2003, which may indicate a shift in the pathogen population in the field. Overall, two sprays of fungicide controlled rust better and yielded more than one spray. Among the one-spray schemes, better results were achieved when the fungicides were sprayed at the booting stage, followed by elongation. The net income associated with fungicidal sprays ranged from R$ -45.35 to R$ 297.58 in 2002 and from R$ -62.66 to R$ 399.08 in 2003, being influenced by cultivars, fungicide, and growth stage at the application. The spray volume of 200 L.ha-1 provided better disease control. The efficacy of fungicides, fungicide rates, grain yield, grain quality, as well as the net income varied from 2002 to 2003, mainly because differences in weather conditions between cropping seasons. The net income was higher as fungicide rates and spray volumes were lower. The chemical control of crown rust proved to be reliable technically and economically for most cultivars, except for the control scheme based on a single spray of fungicide at the flowering stage