MANCHA EM REDE EM CEVADA: QUANTIFICAÇÃO E DANO

Abstract

Among the variables that affect the productivity of the barley crop (Hordeum vulgare L.) are fungal diseases, especially spot blotch (Drechslera teres). Due to the scarcity of information about this pathosystem, the present work aimed to elaborate and validate a diagrammatic scale, as well as to model a damage equation for barley spot blotch. For this purpose, barley leaves were collected at the phenological stage of elongation with symptoms of net spot, which had their severity quantified by the Quant® program and used to make a diagrammatic scale. The scale was validated with 10 evaluators for two weeks. The evaluators estimated disease percentages without a scale, with a previously published scale for this disease, and the scale developed in this work. Analyzes of reproducibility, repeatability, accuracy and precision were performed with the data, and the proposed scale provided values within the parameters. For the damage equation, the incidence and severity of spot blotch in three barley cultivars, ANA 01, KWS IRINA and BRS BRAU were evaluated. The disease gradient was formed by different numbers of fungicide applications. Based on the general barley spot blotch incidence equation, productivity can be reduced by up to 70%. It was found that the incidence of the disease is more representative for calculating damage in the early stages, while the severity is more relevant in the reproductive stages. The validation of the spot blotch equations proved that the equation with the greatest applicability is the incidence in the tillering stage, specific for each cultivar.