Effectiveness of fungicides for controlling Fusarium head blight of wheat depending on the phenological stage of treatment

Ivo Yanashkov, Tzenko Vatchev

Abstract: Although highly variable, preventive application of fungicides is considered the primary means of control on Fusarium head blight (FHB) of small-grain cereal crops. In this research, two field experiments were carried out to identifythe ability of Allegro® (suspension concentrate, 125 g/l epoxiconazole + 125 g/l kresoxim-methyl) and Opera® (suspo-emulsion, 85 g/l pyraclostrobin + 62.5 g/l epoxiconazole) at three timings: flag leaf (BBCH 37-39), heading (inflorescence emergence, BBCH 54-57) or flowering, (anthesis, BBCH 61-65) to reduce Fusarium head blight of winter wheat. Each fungicide was applied alone at the recommended doses of 75 ml/da and 150 ml/da, respectively to plots (2.0 m x 1.0 m) of the wheat in a completely randomised block design. Different isolates of Fusarium oxysporum, F. graminearum and F. culmorum were inoculated, either alone or in combination of the three pathogens together, to groups of wheat heads by spraying with suspensions of spores and mycelium fragments during the period of flowering. Severity of FHB was measured by average percentage of Fusarium-damaged spikelets per wheat head. The highest levels of control were achieved by spraying with Allegro® or Opera® during flowering. Respectively, the two fungicides reduced the disease severity indices as fallows: by 59% and 63% in plants inoculated with F. oxysporum, 61% and 74% with F. graminearum, 5% and 25% with F. culmorum and by 77% and 64% with the mixed inoculum of the three pathogens. Fungicide treatments at earlier timings either flag leaf or heading resulted in a significantly lower reduction of FHB – between 11% and 40% for F. oxysporum and F. graminearum inoculated plants. Some positive reduction of the disease caused by F. culmorum was achieved after the application of Opera® at heading. Application of Allegro® at flag leaf stage resulted in 59% reduction of FHB in plants inoculated with mixed inoculum, while Opera® applied at the two pre-flowering stages had no effect on the disease caused by the mixed infection of the three pathogenic species.

Keywords: cereals; fungicides; Fusarium head blight; phenological stages; wheat

Date published: 2019-10-31