SEVERITY OF RAMULARIA LEAF SPOT AND SEED COTTON YIELD IN DIFFERENT SOWING TIMES

ABSTRACT The ramularia leaf spot (RLS) disease causes cotton yield losses. Choosing a less susceptible cultivar and a sowing time that are less favorable to the pathogen contribute to the management of this disease. The objective of this work was to evaluate the severity of ramularia leaf spot on cotton cultivars sowed in two different times. The experiment was conducted in a triple factorial design (4x3x2), consisted of four cultivars, the three thirds of the plant and two sowing times, with four replications. Each plot was divided in two twin plots, one with fungicide application (with disease control) and the other without fungicide application (without disease control). The severity assessments were performed every seven days, considering each third of the plant with a diagrammatic scale. Yield was evaluated in each plot. There was a significant interaction between sowing times and the thirds of the plant in the plots without disease control for RLS severity, with the highest values of area under the disease progress curve (AUDPC) in the first sowing time (ST1) and in the lower third of the plant. The FMT705 cultivar had the highest and FM951LL the lowest value of AUDPC. The AUDPC of these cultivars were no statistically different in the second sowing time (ST2), but they had higher AUDPC values in the lower third. Highest yields were found with ST1 in plots with disease control, with no differences between the cultivars, however, lower yields were found in plots without disease control. RESUMO A mancha de ramulária promove perdas de produtividade do algodoeiro, em que a escolha da cultivar menos suscetível e a época de semeadura menos favorável ao patógeno contribuem para o manejo da doença. O objetivo deste estudo foi avaliar a severidade da mancha de ramulária em cultivares de algodão conduzido em duas épocas de semeadura. O experimento foi conduzido em esquema fatorial triplo (4x3x2), sendo quatro cultivares, três terços da planta e duas épocas de semeadura, com quatro repetições. Cada parcela foi dividida em duas parcelas gêmeas, onde uma parcela recebeu aplicação de fungicidas (com controle) e a outra parcela não recebeu aplicação de fungicidas (sem controle). As avaliações de severidade foram feitas a cada sete dias, considerando cada terço da planta com auxílio de uma escala diagramática. A produtividade foi avaliada na área útil de cada parcela gêmea. Houve interação significativa entre as épocas de semeadura e terços da planta nas parcelas se