ESTRATÉGIAS DE MANEJO INTEGRADO DA MANCHA-DE-RAMULARIA E MACHA-ALVO DO ALGODOEIRO

Abstract

During the raise of cotton (Gossypium hirsutum) several diseases affect the photosynthetic activity of the cotton plant, such as ramularia leaf spot (RLS) and target spot (TS), causing significant production and yield losses. The objective of this work was to evaluate the effect of different plant populations, chemical control and sowing dates on the severity of RLS and TS in cotton. The test with cotton cultivar TMG 47B2RF was carried out at “Fazenda Progresso” in the 2022 harvest, in Primavera do Leste, MT. The design used was randomized blocks with four treatments and four replications with paired controls. The plant population factor consisted of i) 66,666 plants ha-1; ii) 88,888 plants ha-1, iii) 111,111 plants ha-1; and 4) 133,333 plants ha-1. The control factor chemical management (seven sprays): i) with management and ii) without management with fungicide. The planting time factor was carried out: i) planting in the first half of january, ii) planting in the second half of february. The severity (%) of RLS and TS was evaluated via diagrammatic scale at 96, 103, 116, 122, 129, 136 and 143 days after sowing (DAS) and 150 DAS for TS. The parameters area under the RLS and TS progress curve (AUDCPRLS and AUDCPTS) and the infection rate of RLS and TS (IRRLS and IRTS) were calculated. The production parameters were evaluated: plant height (PH), total number of nodes of the plant (NNo), number of bolls in first position (Nb1), number of bolls in second position (Nb2), number of bolls in third position (Nb3), number of bolls in vegetative branch (NbV), number of total bolls on the plant (NTb), number of abortions in first position (A1), number of abortions in second position (A2), number of abortions in third position (A3), number of total abortions in the plant (TA) and yield (Yi). Hypothesis tests and multivariate analyzes were performed for the different response variables. The severity of RLS and TS of cotton decreased with increasing plant planting density (plant meter-1). The PH was higher in denser plantings (etiolation), however, the other morphoagronomic parameters were lower in lower planting densities. The RLS and TS epidemics were higher in cotton plants grown in january than in february. For plants cultivated in january, PH, NNo, Nb1, Nb2, Nb3, NbV, NTb, A1, A2, A3 and TA were equal to or greater than the plantings carried out in february. Application with fungicides reduced the severity of RLS and TS on cotton. The morphoagronomic impact of fungicide application on cotton plants was not observed.